Making Your Buddy Angry - Tuning Project for a Buddy 50

[az_slynch]

Ran When Parked.

Hey folks! Been awhile since I was last actively posting; life kept throwing me curveballs and my scooter wrenching was always the first think to suffer.

So, a thing happened. Something I never thought would: I own a Buddy. No knock intended on the Buddy lineup here; while I was interested in the mechanicals, the styling never resonated with me. I've written an article for The Scooter Zine regarding buying a used Buddy, if you want more insight on how I regard them.

I came upon this particular scooter while looking for a few extra 50cc project bikes. A friend of mine and I already own several 50cc scooters and thought it would be fun to host a group ride with our little herd. We'd need a few extra ones to make for a decent group and a friend found the Buddy for me in Phoenix. I bought the bike for the project, then promised him I'd soup it up and pass it on to him for riding with minimoto rides up there.

The scooter was a minor project. Overall, it looked good, but the fork was bent and it didn't start. I replaced the steering tube and rebuilt the fork. The carburetor needed a new pilot jet (corrosion) and the variator-side crankshaft seal was shot, leaking fuel/oil mix into the CVT housing. Two seals and a carburetor refresh later, the scooter popped to life with no trouble.

I made two minor changes to the scooter. I swapped the CVT section with an NCY kit, since the belt was thin and the variator face was scarred. I also pulled the aftermarket exhaust (a Silverstone pipe that made noise and not much else) and fitted a MLM sidebleed pipe. These changes really woke up the scoot in the middle of the speed range and made it much more palatable to ride in traffic.

This was completed last year.

The 50cc ride hasn't happened yet. Parts delays due to the pandemic and a few other projects held things up. My friend has been getting antsy to have a fast 50cc ride and sent me an "anniversary" photo of picking up the scoot. I agreed to accelerate the project if he found me another 50cc scooter to sub in for the Buddy. An '09 Aprilia SportCity One has appeared to take the Buddy's slot, so now the build is on!

A friend and I who share a workspace racked the Buddy Wednesday after work and the engine came out. Friday after work, the engine was torn down to the crankcases. Saturday morning, we removed any remaining parts, I removed the crankshaft bearings and cleaned up the crankcases. I'll chronicle the rebuild here and discuss the parts choices.

Please note, I did not come up with everything regarding this build myself. Other forum members have covered this ground (and busted parts on our behalf) before and I've studied their work. I only intend to add more context for other members who want a bit more from their Buddy 50. Credit where credit is due.

[az_slynch]

Here's the brief on what's being fitted to this engine:

• Stage6 HPC crankshaft
• Stage6 Sport Pro Mk.II cylinder kit
• Polini 9.9:1 upgear set
• NCY SuperTrans kit (with more adjustments, 5gr weights, +1000RPM torque spring and +2000RPM clutch springs)
• Polini High Speed variator for Honda Dio (94mm) (1200-1213)
• Malossi carbon fiber reeds for now, studying a possibly better solution
• Arreche 21mm carburetor, 30 pilot, 97.5 main
• Yasuni Carrera 10 exhaust
• Stage6 Performance CDI for Dio

This is not an all-out build. There are racier cylinder kits, taller gears and meaner exhausts available. The goal is to build something quick enough to ride with stock-ish bikes like Groms and Z125 Pros and appear as non-tuned as possible. Admittedly, the exhaust is essentially impossible to disguise, but the chosen carburetor will let me keep the stock airbox housing (with added air intakes on the back) and retain the automatic choke for driveability.

I'll be putting CST 6017 tires on. They're a sportier compound and tread, while keeping the innocuous whitewall look. Forks were fortified with fresh seals and Torco RFF 20 oil to make for a sharper ride, without resorting to NCY suspension and further giving the game away. Rear shock stays for now, but I am looking for something that provides better performance while looking mostly stock.

My friend who will receive the scoot is not mechanically inclined. He's also not a small dude. He knows that this Buddy will need two-stroke oil and more attention then a 4-stroke, but he will fuss if it works any less easily than stock. This requirement will be the greatest challenge, to ensure it's just plain reliable and consistent. This requirement drove a lot of my parts decisions and led me to leave some performance on the table.

EDIT: annotated finding for variator used. The Polini 1200-1210 Hi Speed variator for GET engines is not recommended. See post 35 for detail.

[az_slynch]

Here are some teardown photos. I chocked the front tire, strapped the handlebars to the lift and slipped a few blocks of wood under the lowest frame hoop to support the chassis while the engine was out.

Ready For Surgery.

The Original Build Had A Good Run.

We pulled the underseat bucket to access the fuel, oil and vaccuum lines. I left the carb on the motor for the moment but disconnected the bystarter wiring and the throttle cable. Them we unplugged the starter harness and the stator harness. There is one ground cable connected to one of the intake manifold bolts.

Disconnect These Things.

Disconnect These Too.

I removed the upper and lower shock bolts, then removed the shock for more clearance. We left the rear wheel and exhaust for last.

Now We Get to The Fancy Tools.

[az_slynch]

The next evening's work was to split the crankcases. I'm replacing the crankshaft with a more durable unit that can withstand the additional stress this engine will experience. I've read that the stock crankshaft is good for over 11K RPMs, but I'd rather not snap it and damage the crankcase.

The Buddy 50 engine is a bit fascinating to me. The CVT components are almost all completely interchangeable with a Honda Dio. The stator assembly is a dead ringer for a Honda part and looks to be clocked the same as an AF18 engine. I love the Minarelli-compatible top end since it opens up a lot of cylinder choices. It's one of those great little Taiwanese secrets, like the Kymco Fever II ZX and Sym DD50 being Honda AF16 and AF18 clones.

The sharp-eyed home gamers will notice that the cylinder is marked Airsal. When I was refurbishing the scoot initially, I stuck a basic 50cc aluminum kit on. The stock cylinder still looked good, but the piston had seen some miles and the ring gaps were on the wide side. Additionally, aluminum sheds heat better than iron and it gets fricken' hot here in the summer. I swapped the cylinder and put a Zuma cylinder head to increase compression and give the Buddy a bit more giddyup.

Now then, to work:

Removed the CVT kit.

Time to remove the top end.

I forgot to include a stator picture, but the flywheel comes off with a standard Honda puller.

The final piece to remove is the center stand. Remove the spring before attempting to remove the pivot pin.

Once the top end and crankshaft accessories have been removed, remove the seven bolts that hold the case halves together. There are three long ones, three shorter ones and one that secures the front of the reed block housing. With it was time for my super-secret case splitting tool: a flywheel puller for a Puch E50 moped. Note that this trick works on Honda AF05, AF16 and AF18 too. Be sure to thread the fixture bolts as far down into the stator bolt holes as possible to avoid pulling the threads out. Clean up the engine pivot tube, because you'll have to slide the case half off of it as the tool splits the case.

The abrupt "CRACK!" when things yield, yikes!

[az_slynch]

With the flywheel side case off, I used my Tusk crankcase splitter to push the crankshaft out of the block.

Bye Mr. Crankshaft!

Itty Bitty Crank

The next morning, we pulled the starter motor off and dismantled the gearbox. The final disassembly steps were to drive the crankshaft seals out of the case halves, heat the cases around the main bearings with a propane torch and tap out the old bearings with a punch and an engineer's hammer.

Looks very Honda to me.

Looks sorta Minarelli to me.

Adios, bearings and seals.

Now, time to clean things up and prep for reassembly!

[az_slynch]

The engine can be as dirty as you want when tearing it down. but when you rebuild it. It needs to be clean!

It's Not Just Clean...

I spent way too much time cleaning accumulated grime out if all the nooks 'n crannies, scraping off gasket residue from the mating surfaces and linishing the gasket surfaces, but the results speak for themselves.

Ready to Rebuild.

To kick the rebuild off, I put brand new PGO crank bearings and crank seals in the case halves. OEM bearings are made by TPI in Taiwan. The bearing code is SC04A50. For the perfectionists, NTN also offers this bearing, though I suspect they're not significantly better than the stock part. To install the bearings, I put each case half in the oven at 350F for ten minutes. The room temperature bearings just pop right in. I let the cases cool before installing the seals. I used a socket and a dead blow mallet to install those.

I considered two crankshaft options for the rebuild; BGM/Jasil and Stage6. Here's a side-by-side comparison.

Jasil on left, Stage6 on right.

Both options are rated for up to 16K RPM but have a big difference in function. The BGM/Jasil crankshaft is a low primary compression (LPC) crankshaft and the Stage6 is a high primary compression (HPC) crankshaft. The HPC crank reduces the available volume in the crankcase by having fuller counterweights. This may improve low and midrange pull but can lead to reduced or peaky top-end power. The LPC crankshaft will have less bottom-end grunt but will make broader power at upper revs. The future owner is a bigger dude and the exhaust is a compromise to make more power up top, so I'm using the Stage6 crank in this build.

My only concern at this point is the mass difference between the stock and Stage6 cranks. I might look into having the flywheel "shaved" to offset any weight difference. I've decided against a mini rotor ignition like NCY or HPI at this time, since this is not a race scoot.

Crank gets installed tonight. I need to borrow a press to address the rear gears, but I'll update when more work has been done.

[az_slynch]

No further assembly happened last night, but a bit of component analysis was conducted. I weighed the stock crank and compared it with the BGM/Jasil and the Stage6 cranks. The BGM/Jasil is only about 40 grams heavier than the stock part. The Stage6 crank weighs in a good 112 grams heavier.

1032 grams for stock.

1072 grams for BGM/Jasil.

1184 grams for Stage6.

Wondering if having the flywheel shaved to offset that extra weight would help, since it's possible to remove 100-115 grams of weight from the flywheel.

Stock Flywheel. About 10 grams heavier than a Honda.

Ordered a spare flywheel from Scooter Lounge so I can test this hypothesis.

[az_slynch]

Saw my local machinist to press the transmission gears this morning. Glad it did, as they were not keen to be pressed apart. I used the Polini 202.1321 gear set. In Ohh buddy's thread, they listed this option for lowering the final drive ratio. from 11.5:1 to 9.9:1. Having recently worked another large friend's Zuma 50 down from 14.66:1 to 10.58:1, I didn't want to go too low lest the scoot be unable to climb a hill.

Changing gears.

It's also worth noting that the new gears are straight-cut instead of slightly helical. You may hear a bit more noise from the gearbox.

Final gear comparison, new Polini on top.

The other thread references the use of a 12 ton press. I can confirm this, as we tried using a 2.5 ton arbor press and it couldn't get the job done. We went to the "I wasn't asking" hydraulic and he "finessed" the assemblies apart. Reassembly required similar persuasion for the axle, but little effort from the 2.5 ton arbor for the intermediate shaft. We measured everything and decided to use the assembly anyway, but we did use an anaerobic retaining compound (think Loctite for pressed parts) to reduce the chances of shaft slippage.

This was a bit too small for the job.

Now the engine can be reassembled into a roller. I may test with what I have and swap bits as needed.

[sc00ter]

Your'e bringing back memories of doing this level of tuning on Zuma bug-eyes. I'm just not sure if its a good or a bad memory! Your garage/shop must be heated. I had to cram a kerosene heater under the edge of the motorcycle lift table and put my hands on the table when they got cold! I might pop into my local Genuine dealer and see if the RH50 is on sale. I hear they have a 20% off Black Friday sale going on. I'd be happy with a quality Stage 1 tune myself.

But that Buddy should move when you get it done! Please list a breakdown of what aftermarket parts were used and your base settings/tunes, unless you building a top secret sleeper!

[az_slynch]

Go for it on the RH! I've looked at their engines and they're not identical to a Buddy. The rear half of the Roughhouse case is a convincing clone of a vertical Minarelli, though. PGO did a pretty good job of building a motor that took the best bits from both Honda and Yamaha's designs.

Garage is currently unheated. It's about mid-50s this time of year in the evenings (7:30-10:00P) when we can work and upper 30's - low 40's on the weekend mornings (8:00 - 10:30P) when we can sneak out. We sometimes use a small parabolic heater, but my buddy got a nicer radiant heater that we plan to install after Thanksgiving.

Parts are listed in the second post, I'll amend it with part #s soon to help. The only real unknowns at this point are the carburetor choice and if I use a lightened flywheel or not. I have a 19mm Arreche on-hand and a 21mm on the way. For turning 11K RPM, the calculations say the ideal carb venturi size is 20.7mm. The 19 would be kinder for fuel economy. The 21mm would perform a bit better at the top of the rev range.

Reeds are likely going to just be a CF petal upgrade. I found reference to another reed option, but I want to research more before buying a pricey reed block and hacking it up to fit. Keeping the stock intake too, as I believe it's sized sufficiently for this build.

My shop partner's Zuma hits 55mph on a Malossi 70cc iron kit, Boyesen dual-stage reeds, a Yasuni R pipe and a Top Performances curved CDI with a 3-degree timing advance key. Driveline consists of Athena 15/50 primary gears, early bugeye secondary gears, a Malossi Multivar with 6gr rollers, a Delta clutch/bell with a 2K contra spring and 2K clutch springs and an RS50 belt to get all the low end. The parts list suggests it should be faster, but the choke points of the build are the stock crank (with a Stage6 small end bearing since bike revs to 10500RPM regularly) and the carburetor (rejetted 14mm Teikei). Those two last bits frost me because they really hold the scoot back. Rider is over 300lbs, so I'm impressed it does what it currently does. He's not ready to split the block (proud that the stock crank has 18K on it) and he's worried about economy (on a high strung 2T, really), but I'm hoping this Buddy's performance will change his mind.

[az_slynch]

Hope y'all had a great holiday. They slowed down my work, but fear not, the project is still proceeding.

To get things started after fitting new bearings and seals, the engine pivot tube was fitted and the Tusk crankshaft puller was put to work to seat the Stage6 crankshaft into the CVT side of the case. Once it was seated, I fitted the two dowels that locate the crankcase halves, along with a fresh gasket. Leave the sprues on the gasket until assembly is complete. The stator side casting was wiggled down over the pivot tube and located on the dowel pins.

I'm going to detail the Tusk tool quickly since it is seldom demonstrated in detail. It's essentially a pair of concentric tubes. The inner tube has a threaded collar that goes over the end of the crankshaft and is retained by wither the crankshaft nut or a special threaded insert. I used the crank nut in this case but slipped a slightly larger washer between it and the collar to ensure a snug fit.

The inner tube with the threaded rod is threaded onto the collar at this point. Note the peg sticking out the side; it is used to locate the inner tube within the outer one and keep them from twisting respective to one another.

Once the inner tube is snug, slide the outer tube over the threaded rod, flange end down. The slot for the peg is generally aligned with the Tusk logo. Seat the flange flush against the crankcase to ensure a straight pull and reduce the risk of case damage.

Thread the big nut over the protruding threaded rod and lift the threaded rod until the nut is snug by hand. check the seating of the tool flange and alignment of the crankcase pins before applying a wrench. As you tighten the nut, the case halves will be pulled together. Do not rush this job! When pulling the crank into the CVT side, hold the crankshaft's connecting rod so it doesn't swing out and get caught on the case half.

Next, we'll button up a few other details and hang the engine back in the frame.

[az_slynch]

With the cases pulled together, remove the Tusk tool. Locate the seven bolts for the case halves and run them in finger tight. The shop manual calls for a torque value of 1.0 kg/m to 1.2 kg/m, which my torque wrench does not register. For non-metric users, this range falls between 87 and 104 inch-pounds. I set the torque wrench to 100 inch-pounds to err on the side of snug. Pull the wrench slowly so you can stop as soon as it clicks/beeps/bends to an appropriate value.

The Protruding Bits of Gasket Need To be Trimmed Flush

I scored the gasket sprues with a craft knife and folded them before trimming them off. Try to get them flush, as they intersect areas that will also need to seal with gaskets. I didn't use any Yamabond or Threebond, as the gasket was plastic-impregnated and would deform to fit the mating surface.

Polini Secondary Gears In

Dropped the secondary gears in and checked the lash. All looked proper and the teeth were fully engaged. I added the Belville washer to the intermediate shaft, with the cone pointing up. The thrust washer followed it. Note the wear patterns on these two washers if you're uncertain of their orientation when re-assembling. The two dowels were fitted along with the transmission gasket. All six bolts were hand-tightened and then torqued to 100 inch-pounds. Note that the two long bolts go in the holes where the dowels go, and the shortest bolt goes in the hole to the left of the input shaft.

Refit the Oil Pump - Mind the seal and Washer

The oil pump was dropped in at this point due to ease of access. Note that there is a small washer that goes in the case just below the pump gear. I tacked it onto the bottom of the gear with a dab of assembly lube. Don't forget to replace the O-ring that fits under the pump or you will have an air leak.

Stand, Starter and Stator On

The final parts fitted were the stator, starter and stand. The sharp-eyed home gamers already see the goof: route the stator harness up around the back of the block before fitting the starter and stand. Both harnesses route up around the rear of the case and are secured by a clip that attaches to the reed block. Since I wanted to make the Buddy a roller again, it made sense to get those harnesses tidied up with fresh tape and routed before there was a wheel in the way. The final piece to go on before reinstalling the engine was the stand. We're go for engine installation!

[az_slynch]

I've gotten a bit behind on documenting this project. Progress has been made though; it'll be fired up by month's end.

The engine was refitted and new P-rated whitewalls were popped onto the rims. My friend wanted "race tires", but let's be honest here: It's a Buddy 50 and if anything, the whitewalls add to the "sleeper" factor. The P rating is a bit silly for purpose as well, yet there are few "sporty" treads that come with whitewalls.

Back on Two Wheels

Sporty Tread

The flywheel came back a bit trimmer, having lost 90 grams of mass. Not sure how much this will help performance yet. Fan bolts up with no issue. For other folks considering this mod, an AF18 Dio flywheel might be a better option since it is 10 grams lighter to begin with and reportedly can be lightened down to ~575 grams.

Trimmed Flywheel

90 Grams Lighter

[az_slynch]

The transmission kit received a bit of tweaking before fitment. The NCY kit comes with 9 gram rollers and a +1000 RPM torque spring. The clutch springs are red, suggesting a +2000 RPM rating. I left the clutch springs be based on that assumption but upgraded to a +1500 RPM spring. The kit comes with a torque reduction seat and a pulley half with two different variation curves. I used a new fixed sheeve with fresh bearings and a new upper spring seat.

Easy to change with the right tools.

1000 RPM spring came with the kit.

Comparing the springs.

The driven assembly without springs.

Ready to go!

[az_slynch]

I swapped in 5 gram rollers to liven things up. Stock belt and a new fixed variator sheave were used with along with the NCY kit. Those holding tools are pretty handy for these jobs. Both the crank nut and the clutch bell nut were tightened to 28 ft. lbs.

5 gram weights.

Makes torquing assembles a bit easier.

Ready to go!

[az_slynch]

Worked out of town last week, then came home sick for the weekend. The project had been on hold for lack of some small parts, so this update brings us current.

The Stage6 Pro Mk.II Sport kit is a bit different than most. The cylinder head is recessed into the bore about 2.5mm and seals with an O-ring. This makes it a bit more interesting to set the squish. The kit comes with a selection of metal shims of .40mm, .20mm, .15mm and .10mm thickness, in addition to a paper base gasket. After mucking around with Verniers and spitballing the squish, I considered the cost of the kit and decided more precise measurements were in order. Following some guidance I'd found online, I procured some .050" rosin core solder from the hardware store and bent a piece into a "W" shape. The point of this is to spread the solder across the piston crown over plane of the piston pin. The piston can rock slightly in the bore, but the area over the pin will remain consistent. I slipped the shape into the bore, installed the head, torqued everything to spec and rolled the engine over with a wrench several times until I didn't feel resistance from the solder. The head came off, out came the solder and in came the calipers. Squish measured out at .77mm over the piston pin. I swapped out the .15mm shim for a .10mm to bring it down around .72mm; Stage6 recommends a squish of on .6mm and I could have gotten closer but I'm trying to leave some margin on this build. Big rider, hot summers and all that.

Use rosin core solder. Acid core can damage stuff.

In other build threads, there was a fair bit of discussion over spark. This Buddy's stock coil wasn't exactly new, so I opted to snag an NCY coil to liven up the spark. I'm ambivalent about the plug boot, though. It seems to have a hard time yielding enough to properly seat on the plug. I'm considering trimming the wire length a bit, so this will likely receive more attention.

New NCY coil to deal with the compression and revs.

Two showstoppers finally arrived. I needed a silencer gasket for the Yasuni pipe and nobody seemed to have them Stateside. Now I have a few spares for the toolbox. The Carrera 10 is a sharp looking pipe and I was glad to get one to try out. Performance is reported to slot in neatly between the Yasuni R and the Yasuni C16 pipe. I have an R on a buddy's '05 Zuma and while it pulls well, it can't rev on as high as a C16. Conversely, the C16 comes into its powerband a fair bit later than the R. So, we're splitting the difference and hoping the clutch tolerates it. The C10 has a restriction in the header end of the pipe, but not in the silencer. I used a Dremel to grind the welds for the restrictor and pulled it. The final piece to mount this pipe on a Buddy comes from the Yasuni Z hardware kit. The Z comes with two mounting brackets: a short one suitable for PGO motors and a longer one for Yamaha Minarelli motors. While both brackets come with the Z pipe, only the longer one comes with the R and C10 pipe. You can buy the Z hardware kit separately from the pipe if desired.

The other bit I needed was a set of carbon reed petals for the new reed block. Ideally, I wanted to fit a set of Moto Tassinari VForce 3 reeds, but the listed part (V352A) will not bolt on. I also looked at the V384A and it's even less likely to fit. The neat bit is that the reed assemblies pop apart, so the reed cage and stuffer can be removed from the base plate. I believe with a bit of solid modelling that I can get an adapter whipped up to use the 352A parts in a modern PGO intake tract. I'll be fiddling with this later, since I want this scoot running before month's end. So, beefier reed petals for now.

Missing pieces are here.

Restriction removed from the exhaust header.

Planning to assemble the intake and exhaust this weekend. May drain the tank to put 93 octane in. Drained the oil tank to scrub it out and fit a new strainer. Might start the engine off on Motul 710 to see how things go, but I also have a bottle of Klotz for autolube to try out. Decisions, decisions.

[sc00ter]

As much as I love reading this thread it makes my eye twitch! Two stroke tuning is not for the faint of heart. I missed a MLK sale at my local moped dealer (yes, I have a full blown moped dealer in my area. Fusion Cycles) as they had the regular RH for $1999. Oh well.... ya snooze ya looze. But I saw this today, it's slightly off topic.

I see a pokey China scooter up ahead in traffic. As I weave thru to do a pass, just to give him a wave, something else blasted past the China scoot! What was it? A ONYX RCR! Just when I stopped lusting at the CTY 2 I see a RCR in my area! Pretty cool and VERY quick!

[az_slynch]

Got some work in last Saturday. Buddy had been off the lift while awaiting parts and I'd been tearing down a basket case Vino 125 in preparations for import 4CW mods.

First bit on the Buddy was the exhaust. I started by comparing the bracket that came with the C10 pipe and the PGO bracket I had left over from a Yasuni Z pipe. The C10 bracket will not bolt up to the Buddy block, and the Z bracket didn't line up with the new pipe mounts. Took the bracket to my machinist to have a new mounting slot cut out on the Z bracket.

Comparing the brackets.

Z mount scribed with new slot location.

In the interim, I assembled the pipe with the wrong mount in order to mock everything up and ensure it fit the Buddy properly. Clearance is pretty good, though the header pipe does get a bit close to the lower frame hoop when the scoot is on the centerstand.

Check out the header to frame clearance.

Pipe flatters the scoot's figure.

For comparison, I included a picture of the pipe that came with the bike. It's marked Silverstone and is supposedly made in Italy, but I have my doubts. For all the flashly looks, this pipe made zero performance improvement to the scoot. The MLM sidebleed had a far more noticeable impact. The silencer was originally anodized red and still shows the color on the tire side. I chose the red Yasuni silencer as a nod to it's original look.

New hotness meets old and busted.

[az_slynch]

Next bit to address was the reed block. I would still love to fit a VForce 3 in this thing, but time is not on my side. For now, I'll sub in some Malossi carbon reeds.

Shiny new reed block and gaskets.

The scoot got a new stock reed block. The original one had a crack running from a corner of the reed cage out towards one of the rear bolt holes. No air leak yet, but why take chances?

Out with the fiberglass, in with the carbon.

I went with the medium thickness reeds to start the tuning. Malossi includes those same reeds with their 70cc Minarelli kit, so I figure it's a safe bet.

Ready to install.

With the reeds ready, I dropped them into the case with new gaskets. I included a look into the block to show why I think bigger reeds could be used; the inlet area is huge!

Intake area suitable for a much bigger scoot.

[az_slynch]

Fitting the manifold is pretty straightforward. There are four 8mm bolts and the shortest one goes in the back corner closest to the CVT.

Ground lug location.

The bolt in the front right corner receives the engine ground cable.

Wire manager for the starter and stator fitted.

The bolt in the right rear corner receives the engine wire manager. This keeps the starter and stator wiring off the tire. I did have to fiddle with it a bit to get everything to hug the block, but it's still a close fit. I put the starter wire on one side of the intake manifold and the stator on the other and shimmied everything as close to the block as possible before bolting the wire manager down fully.

Not a lot of clearance here.

[az_slynch]

I fitted the carb next. The carburetor I used is an Arreche 21mm. It was chosen based calculations for optimum volume at 11K RPM, as well as it's ability to support the bystarter and fit behind the factory air filter housing. The carb matched up beautifully to the intake spacer. The only annoyance when bolting it on is that the carb body is not threaded and you must use the included square nuts to fasten it to the manifold.

Checking the fit of the carb on the intake spacer.

Connecting up the throttle cable was relatively straightforward, though I did have to cut the cable boot off the stock throttle cable. After cranking all the adjusters in, I was able to connect the cable to the new throttle slide. I swapped out the carb top for an included one with an angled cable guide for best fit. The throttle opens the slide fully once the cable is adjusted up.

Throttle cable fitted and adjusted.

The air filter slips onto the carburetor with no fuss and hides the bigger carb nicely. Yay! I'll be adding some additional intake area to the filter housing to ensure the engine is properly fed. I can use the old filter housing to model a solution.

Stealth mode engaged.

The last bit to address is the fuel, vacuum and oil injector lines. I ordered some new Motion Pro premium Tygon line, which arrives Friday. The stock fuel line fits, but I intend to tweak things a little. In the last pic, the line bends back almost 120 degrees to align with the carb's fuel barb. It also has to bend around the filter housing's intake a bit more than I like. The stock line is molded and doesn't appear to buckle, but with a hotted-up motor, I don't want fuelling to become an issue.

That's a bit of a redirect for fuel flow.

[az_slynch]

As of Saturday morning, the exhaust is mounted properly and the new Tygon fuel line is fitted. I flushed out the oil tank with Brakleen (CFC free) and replaced the autolube system's filter. Put the battery on a charger to top it up, since the meter was only showing 12.2V.

I'm going to drain the fuel tank and put 93 octane in. Picked up some Motul 710 for the oil tank. I need to grab a few fresh plugs so I can plug-chop it after running the initial heat cycles. Very close to firing this thing up!

Exhaust mounting complete!

Very close...ready for autolube oil and 93 octane.

I'd like to discuss the carburetor some more. I chose an Arreche carburetor for this build. As stated, I had a few reasons to go with this brand.

• Compatible with the factory intake manifold and air filter assembly

• Configured to utilize the bystarter assembly

• Compatible with the stock throttle cable

Left side of the carb: overflow and oil injector.

Right side of the carb: fuel barb, breather port and bystarter fitting.

The specific model of the carburetor is 821/3. It has a 21mm venturi, a two-stroke style atomizer bush, mixture adjustment and uses Mikuni-style jets. That last item is important to know when choosing jetting for these carburetors. While other carburetor manufacturers like Keihin and DellOrto identify their jet sizes by physical size, e.g. a 95 jet has an orifice diameter of .95mm, Mikuni and Arreche define their jets by flow rate. In a nutshell, a Mikuni 90 jet is not equivalent to a Keihin 90 jet. There are several jetting charts online to help compare sizing and I recommend looking into them is using a Mikuni or Arreche carb.

Factory jetting: 20pilot and 90 main. Black stuff is casting residue, it cleans off with an SOS pad.

The 821/3 comes with a 90 jet, in 4/042 style. The equivalent sized Keihin jet would be a 98, which might be a bit rich for this build. I have a Polini kit which comes with a range of Mikuni jets, but it changes in steps of 5 and my next size down is an 85, which roughly equates to a Keihin 90 jet. I ordered a few intermediate jets from Treatland in order to have a few more options to dial the scoot in.

My plan is to set it up rich. Tucson has an altitude of 2600 feet ASL, but the owner lives in Phoenix (1200ft ASL) and will likely take it to SoCal (effectively sea level) for group rides. A friend's previously-mentioned 70cc Zuma runs fine in Tucson on a DellOrto 92 jet. We found that it needed a Dellorto 96 jet to run happily in San Diego. That setup will still run in Tucson, but the scoot is down a little in power. Considering how involved swapping jets on a bugeye Zuma is, he can live with it for now.

[az_slynch]

Fired up the Buddy last night.

Primed the autolube system with Motul 710 and confirmed that the pump was working properly. Put a capful of Motul 710 into the 2/3 full tank as an insurance policy, then primed the carb. Installed the stock airbox with the inlet restrictor removed. I had initially backed the idle screw (slide stopper) out until the slide stopped moving down but had to wind it in 1/2 turn for the engine to idle. Still need to fine-tune the idle mixture, but it's not too far off.

Ran two heat cycles, consisting of 5 minutes of idle with a few throttle blips to keep the pipe clear, then allowing it to cool for fifteen minutes. I want to run one more heat cycle, and then drain the tank of premix and put fresh 93 octane in. I also need to install a temperature probe on the engine for break-in riding.

So far, I'm pleased. It's a bit rowdy when you goose the throttle. Revs come on briskly and return quickly to a tame idle. Good signs, but fine tuning, some plug chops and a temp gauge should make it even better. I can't wait to start breaking it in on the road, but the forecast looks like rain until the weekend. More to report then.

[az_slynch]

Ran the third heat cycle last night. Scoot had been sitting since Monday, but fired up immediately and settled into a smooth idle. Shut it down after five minutes and drained the fuel tank in preparation for non-mixed fuel.

Ordered a temp gauge for testing when I got home. Also set out my borescope so I can pull the plug and check the cylinder before road testing. Likely that's overkill since it's running so well, but I might as well use the tools at my disposal to ensure all is well.

[az_slynch]

First road test yesterday in the neighborhood by the shop.

Rollout is decent for a 70cc street kit. The power and pipe hit at 10 bmph (Buddy miles per hour). Power comes on immediately and unloads the front forks noticeably. Within a block, the speedometer is indicating 45-50 bmph and there's a stop sign to attend to.

While it has new pads and a new rotor, the scoot feels a bit under braked. I've been closing down the throttle early to allow more braking room. I suspect I'll be ordering an NCY 200mm floating rotor soon to help manage the braking better.

Temp gauge and tachometer are being delivered today. The owner has registered it, so we'll be able to do more investigative road testing soon. I'd like to identify all the areas that need work before I order more parts.

More to come when the weather cooperates again.

[az_slynch]

Took a test run this evening. I hit the avenue east of the shop, as I had a half mile without any stop signs or traffic lights to worry about. I warmed the scoot up first, them cruised out to the avenue and gave it the beans.

As it did it the neighborhood, the Buddy reared back a bit and zipped up to 48bmph indicated within the span of a block and stayed there. I turned at the light, cruised back down through the neighborhood and ran it again. Same result.

Rode back to the shop and pulled the CVT cover. Apparently, 5gr rollers aren't enough for this setup. The belt is hardly coming out of the low range.

Wait, it's supposed to variate?

Wednesday, I'm going to scribe the variator with a Sharpie and stick a set of 6gr rollers in.Hoping it won't be too fiddly to figure out the lightest configuration to drive the belt up with.

I also intend to tweak the mixture a bit more. Starts quickly and idles well. Revs clean and returns quickly to idle. However, it will sputter off after about a minute of idling. I suspect this is a symptom of a rich idle and can be addressed with a little tweaking. I also have the next size down idle jet if needed.

[az_slynch]

After last Monday's testing session, I put a bit of thought into the CVT function and decided against upping the roller weights. Instead, I swapped the rear torque spring, changing from the yellow +1500RPM spring back to the black +1000RPM spring. Only tested briefly due to high winds and rain/snow moving into the area. A quick check on the lift confirmed that the CVT was variating fully, so I hit the streets. Had to test on a different street due to weather, but I managed 56.6mph GPS despite an 18-20mph crosswind.

The belt wore my Sharpie mark down to the edge of the variator, which suggested the only gains left were going to come from increasing engine speed. I wasn't quite keen on that plan, so I did some research when I got home on Honda Dio CVT tuning and placed a late-night order for a Polini High Speed variator for 50cc Ruckus. The part arrived on Friday (thanks Treats!). The good news is that it's a bolt-on part for a Buddy. The better news is that the drive face is 94mm (compared to 89mm for the NCY variator) and comfortably clears on the starter gear support. I kept the 5gr NCY rollers and Sharpie'd the drive face, then set out for another run. My GPS app failed to log, but that was the first run where I saw the speedometer needle clear 60bmph.

Saturday, I had my shop partner with the Zuma (who weighs 65lbs more than me) try it out. He managed 55mph GPS and was pretty impressed with the overall performance. I spent a bit of time fiddling with the mixture screw to address a bit of intermittent "rev hang" when returning to idle after a hard pull. The plug looked a touch lean, but the scoot ran well. The Buddy's owner was coming down the next day, so I left it in what seemed like a decent state and started digging into another scooter project for a bit.

Sunday, I decided to test the Buddy on a set of 4.7gr Malossi rollers we had. Acceleration got a bit feistier, but it seemed like I lost a little top speed. As it was wrapping out on the I-10 access road, I felt the power "nose over" a bit, so I rolled out some throttle and blipped it a bit to slow it while keeping a cool charge on the piston. The Scoot ran fine back to the shop and a plug check showed good wash on the piston. My GPS readout was 55.2mph, but the variator didn't top out with 4.7gr weights. I swapped the 5gr weights back in, then opened the carburetor and raised the throttle needle by one notch. It felt fine after a test run, so I chalked it up to needing a scoche more fuel at the top end.

The owner arrived and took the scoot out for a few five-mile laps. It ran well on the first lap, but I cautioned him about it "nosing over" at max speed and advised him how to address it. He commented how it was a bit rich transitioning from the pilot jet to the main jet. I added an 1/8th turn on the air correct and sent him out again. The 1/4 throttle richness smoothed out, but it nosed over on him at max speed. When he got back, I decided to upsize the main jet. I swapped in a 92.5 Mikuni (equivalent to a 100 Keihin) and left the needle as-set. I also realized I hadn't installed the Stage6 CDI for Dio, so I popped the front cowl off and installed that too. Took a quick run to the filling station to top it off and was a bit surprised to find it now pulled like it had on the 4.7gr weights. He went out for another lap and saw the speedometer climb to 63bmph, which came back as 59mph GPS. It ran great and had zero issues on that run or the subsequent, 10-mile run.

I have a few things to address. First, I want to poke the borescope in the cylinder tonight for a health check. I also want to ensure the plugs I picked up fit the Stage6 head properly, since it is thicker than the stock head. Next, I want to swap the plug. It currently has an NGK B8HS. I don't believe that the NCY red coil has a resistor in the plug cap, and I noticed that when the Buddy was revved on the lift, it would trigger the LEDs on my Milwaukee impact gun from two feet away. That's a bit of EMI! So, a resistor plug it shall be. Thirdly, I'm looking for a heavier-duty belt than the stock one. This engine is putting down some decent power now and we noticed some possible slippage at the end of the day's testing. This one may be tough to address, as the belt is an uncommon size. More homework is in order for that one.

This scoot would be a bullet with a lighter rider on it. I see a marked improvement in performance compared to the owner, who weights 25lbs more than me. I want to find a skinny rider with a need for speed to test it. For now, I'm going to check the cylinder, swap the plug and test it again tonight...with my GPS app running this time. I'm pretty sure I can hit 62-63mph GPS. Debating if it would be worth trying the 9.5:1 gears, or if it would be worth trying a C16 pipe. In either case, I'd be trading some acceleration for top speed. Stay tuned!

[az_slynch]

The borescope inspection was a pleasant surprise. After having it "nose over" twice, I was worried there had been a soft seize. The picture speaks for itself:

Piston crown looks good so far. No galling marks on the walls.

Borescopes with photo and recording capabilities are pretty cheap these days. I can't recommend one enough if you routinely mess with engines.

Spark plug is now an NGK BPR8HS. Scoot runs fine and it no longer triggers the lighting on my Milwaukee driver when revved.

Now, data:

Not too shabbly.

Other Buddy 50's have gone faster. They're also running taller gearing and carrying riders that are significantly lighter than the owner and myself. Acceleration in traffic is impressive and arguably more valued than top speed at this point. I am going to set up a second set of final drive shafts with the 9.5:1 parts to test and then we'll decide if the extra speed is worth the decrease in acceleration. There doesn't look to be any space for a variator bigger than 94mm, but I will see if an RRGS/JISO 97mm variator has a shot at fitting. There may be a touch more speed if we switched to a C16 pipe, but I don't believe the extra 250rpm peak on the pipe is worth the delayed onset of power and it'd be another $280 + shipping to find out.

For in-town use, this setup seems about perfect. Top end is just short of the 65mph goal and I'll try the few things mentioned above to see if we can get there. Realistically, I told the owner to get on a diet before the SuperSunday ride in late April.

I'm installing the tach and temp gauge tonight and will continue to look at the data and fine-tune it, but I think the build parameters defined above are a solid choice. I'll continue documenting the run-in and note how it holds up for the riding over the SuperSunday weekend.

The other goal was met too: we're throwing the 55mph Zuma on the lift this weekend and tearing it down for similar upgrades.

[az_slynch]

200 miles in and Angry Buddy needed a new piston. It's already fixed, but I made minor changes to the build:

• Squish changed from .72mm to .82mm

• Main jet changed from Mikuni 95 to Mikuni 100

Things got a bit lean due to heat. It may have been slightly under jetted or just had too much squish. The piston crown showed signs of detonation and melted a bit near the ring locating pin, causing a loss of compression. The head O-ring had melted and squeezed out of it's groove, which could had added an air leak to the problem.

I changed the squish based on a Stage6 blog post for the kit which advises setting squish between .75mm and .85mm, in contrast with the included manual, which specifies a squish of .6mm, +/- .10mm.

Jetting would probably work well at 2300ft with a Mikuni 97.5 main jet. I jumped up to Mikuni 100 to see if the engine got fat up at the top of the rev range (it does) and to have it ready for the 1200ft elevation in Phoenix. I will likely need to upjet to a Mikuni 102.5 to keep it safe in LA this coming weekend.

Ran the new cylinder in for 45 miles last night with a capful of Motul 710 in the tank. I'll probably do that for the next three tanks as recommended in the Stage6 blog to try in improve longevity. Replacing a $100 piston every 200 miles isn't very cost effective.

I'll follow up after SuperSunday.

[az_slynch]

I'm thinking it might have needed a Mikuni 105.

My friend who owns the Buddy tried to go full blast up the Long Beach International Gateway and popped it at the top. That's a tough ask when a 300lb rider is involved.

Back to Tucson tomorrow and back to the drawing board. Might take a bit more squish out too.

[az_slynch]

Long overdue update. I've had work projects, a trip to Chi-Town to see family, a local club rally to help run and several other project scoots across the lift since this Buddy was blown up. Frankly, I was also a bit peeved about it and not keen on letting the owner queue jump when I have project scoots that have been waiting a decade or more to get attention.

Autopsy completed. Big hole blown in the piston. Piston chunks everywhere. I can clean up the cylinder with muriatic acid and the head is still usable. I may pair those with a fresh piston as a cold spare. Putting a fresh kit on, replacing the main bearings/seals and having the crankshaft inspected by a good local shop.

Parts ordered from ScooterLounge and Treatland. I found a larger pilot jet for the Arreche carb, but it looked like Talleres Arreche might have stopped licensing the Amal 400-series carbs and both carburetors and parts are drying up; I'm hoping I'm wrong about this.

The plan is to to up the pilot again from a 25 to a 30. The coil will be downgraded to stock to reduce spark intensity (and hopefully heat) and the cylinder squish will be increased to .85mm to help with heat. We'll see what that does to performance.

I was hunting for details from a Taiwanese shop about a mechanical ignition retard for the Honda AF18 engine, but not getting a lot of detail. A programmable ignition that can be used to retard timing by 6-8 degrees at engine speeds over 9K would work, but I'm loathe to pour more cash into a bike that isn't mine.

Parts should all come in after the New Year's holiday and I hope to have it back on the road in January.

No bueno.

Head looks reusable.

Bore can be cleaned up.

Piston debris in the crankcase.

[sc00ter]

I've pretty much quit wrenching on stuff BUT your build thread might get me motivated again. Only scoot I would consider is a RH50. Common, simple and still be manufactured (for now). That piston popping at the top sucks! I hate having to split a case open to replace main bearings. If I get back into a 2-stroke I'll keep it simple. Maybe a cast iron 70cc at the most.

[az_slynch]

sc00ter,

Do It!!!

This little scoot has been a blast to work on and I wish I hadn't agreed to give it to my friend. The biggest reason for the meltdown was that he really isn't familiar with 2T operation and he closed throttle at high revs after a long uphill pull; temps went sky high and the piston followed suit! While the timing might be a touch spicy and the pilot seems a bit small, it has run great while I was riding it during break in. Very civil at low throttle and plenty of usable throttle range, but it would go like hell if you put the spurs to it. I may look for a RH to mod for variety, but I'd grab another Buddy 50 now that I have some experience with this engine.

I have an '09 Buddy 150 St. Tropez now; was a customer abandon at a local shop that was too nice to let rot. Doing the basic R&R on that in tandem with the 50 rebuild, then digging into a $100 XCiting R 500i that I stashed away.

[sc00ter]

Wowzers! The RH50 goes for $3199 now local/$2699 if I wanna drive a bit. Both prices are before the dealer throws in the hidden fees: like registration, PDI and all that stuff. I'm currently enjoying my ebikes more at the moment, so I'll have to do a little soul searching. I don't have space for multiple vehicles. I actually got fussed at on Friday (12-29) for not having a 2-stroke by someone who knows me from my Zuma days. Weird that anyone would remember me from the Zuma's, as mine were always beat-up (but very fast).

I might look for a used RH50 but I'm very picky on condition, and the few I've found are ratty and tatty. If anyone drops it it'll be me first!

[az_slynch]

If you don't read the rest of this post, here's the key point: Do not underestimate the importance of dry builds.

If you're still following along, here's the parable. I had to split the crankcase to clean up the piston carnage. There were blobs of aluminum in the pockets for the crankshaft counterweights, in the oilways from the transfer ports to the bearings, wedged between the reed block and the crankcase and even in the gear drive well for the autolube pump! All of it had to be cleaned. The crank seals were pulled and tossed and the crank bearings, full of aluminum slurry, were tossed.

After cleaning the case halves thoroughly, I fitted SC04A50 C4 bearings for a a bit more tolerance at high revs. I'd ordered them from Treatland. Amusingly, the order page listed the bearings as NTN, but I received TPI bearings, the OEM brand for the Buddy. Cases went back in the oven to drop the bearings in and new crank seals were fitted.

Spline damage.

Ramp Plate ovalling.

Drive face spline damage.

While cleaning everything, I gave the crankshaft a good look over and found a subtle issue I'd missed on assembly. After checking the crank runout on a truing stand (it was still OK), I noticed a few dents in the transmission side splines. It looked like the area where the variator ramp plate would rest; I checked the ramp plate and noticed similar grooves to the splines and a tiny amount of ovaling of the ramp plate hole. Initially, I suspected it was due to the Polini ramp plate not being keyed for a spline like the factory ramp, but the NCY ramp wasn't keyed either and I hadn't seen any other report of this issue. I decided to stack the whole transmission side of the crank up to see what was going on. Once assembled and the nut was torqued down, there was still a tiny amount of play in the assembly. I'd missed it when swapping the variator on the scoot because the CVT belt was putting a small amount of tension on everything.

NCY Dio boss.

Polini GET boss

The culprit turned out to be the variator boss. There are subtle dimensional changes between the GET variator boss and a Dio variator boss. The GET boss is .4mm shorter than a Dio boss, The upshot is that even with the washer installed, the crankshaft nut was bottoming on the splines before clamping down the parts on the shaft. I measured the boss from the NCY boss and checked the Polini documentation to confirm my findings. I also found that the Dio boss is about .02mm smaller in diameter, so while the Dio boss fits in the Polini GET variator, it's a slight interference fit and will not function smoothly. A new Polini Hi-Speed variator "for Dio" (pn 1200-1213) will arrive next week. I also have a new drive face for the variator, since I'm pretty sure the looseness of the assembly was causing the spline wear seen earlier in the build.

There is still a risk that the ramp plate could shift due to the dented splines. I'm considering having my machinist cut in a tiny register in the inside of the ramp to keep it located. It'd be cheaper than a new crankshaft ($187 at the time of writing) and since it's not my scooter, I'm not keen to keep dumping money into it.

One other upside of the dry build: I weighed everything on the CVT side of the crank for comparison with the lightened flywheel. It's under 30 grams lighter, but not too bad all things considered.

CVT side with 5gr rollers in it.

[az_slynch]

Small update. I received the Polini 1200-1213 Variator set, which is reportedly good for 4T Kymco 50s as well. It's not quite a direct fit, as the variator boss is a good 2.4mm longer than the one in the Polini-1200-1210 kit.

Since the crank had that spline damage, I had my machinist cut a .5mm register into the new ramp plate and the variator boss to keep those two parts aligned. When assembling the parts, I found that the kickstarter pawl would have reduced exposure to the crank spline, so we faced the new fixed pulley by 1mm for more engagement. The end result fits together well and torques up properly. When assembled, the belt sits closer the boss in low gear and the belt sits closer to the top of the driven pulley, improving the range of variation.

I just picked up an RRGS/JISO pulley for AF16 Dio which opens another 1mm over stock to see if we can get a bit more out of the upper range of the CVT. This means tossing the NCY torque bearing to get more torque spring range, but we'll see if it has a noticeable impact.