Carb tuning help (can't break in only runs on warm up)

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87PGOSTAR50GUY
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Location: Seattle, WA

Carb tuning help (can't break in only runs on warm up)

Post by 87PGOSTAR50GUY »

Hello, I am in the process of trying to break my scooter in but it only runs when cold (think its only running on the enrichning circuit.)

The idle stop is about 14-15 turns to remove, came preset 13 turns out, runs and starts on at 12 1/8 turns from the bottom.


The mixture screw I am not sure of, played with it today was already pretty much bottomed out when I checked the plug seemed to rich and oily wiped the plug now its to lean to stay running. Only dialed it out for only two turns I reset it back -2 til I can get an answer from someone.


I'm on my second plug, as the first finally full fouled out idles fairly on a 0.40 NGK gap but does not run from 0.06- 0.38.



Its a pgo keihin copy 19mm x 35mm its 42mm at the bolt mounting.


With the 12 1/8 setting after warm, it starts when I add 1/4 / 1/8 throttle as if the needle in the slide needs to be adjusted.

After its warm its pretty much walk away and come back next day. Or wait til cold.



Solutions? Can the mixture screw exceed 2 turns counter clockwise?

If I'm running lean that means that the mixture screw has to exceed 2 turns in order to meet the differance if the enrichner is too rich and makes it run.
CROSSBOLT
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Post by CROSSBOLT »

Mixture screw is air not fuel. Too much fuel and not enough air if screw is nearly bottomed. Good starting point is 2.5 turns from bottom for idle when warm. This bypassed when cold with the "Autobystarter" or "electric choke" devices. when warm this device closes and the mix screw comes into play. All this confirmed by your read on the spark plug.

Karl
87PGOSTAR50GUY
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Location: Seattle, WA

Post by 87PGOSTAR50GUY »

CROSSBOLT wrote:Mixture screw is air not fuel. Too much fuel and not enough air if screw is nearly bottomed. Good starting point is 2.5 turns from bottom for idle when warm. This bypassed when cold with the "Autobystarter" or "electric choke" devices. when warm this device closes and the mix screw comes into play. All this confirmed by your read on the spark plug.

Karl

Fixed it before your message was received,, plug is oily on the back side a tiny bit but I see the chocolate brown tan color close to the tip.


Now operates on correct plug gap 0.06- 0.07mm


Which is 0.27- 0.28 on standard gap .


I have a tiny leak in the head a bit can I spray copper spray on it and call it good? If not I'll just break it in. Goes 40mph max right now but my main concerns the leaks. If applicable I'll pull the jug enough to pull out the e clip and take the jug out with the piston in the bore.


No adjustment needed to the mixture screw dialed the idle in at 2 1/8 turn.



I think I should not run 87 octane pings and knocks like a sob after I dropped my premix 92 octane it pings more, all I know is I'm not lean per say but I know i am doing a compression test. asap to see if there is any leaks at the base the head gasket I don't trust for crap.
sc00ter
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Post by sc00ter »

It is very hard to help someone tune a carb from a distance, that is why a good local club may come in handy. Do some searching, reach out, offer food/beer if someone replies and get it running. I see you did not do a compression test first, you will just chase your tail in a circle if you have even the smallest leak. I had a main seal start to fail, and I chased the "hang-on" at idle for a whole day before I decided to just check the compression to shut my friend up-he was right though, I had a leak. Replaced the seal and then I had to reset the whole idle side because I didnt write down the base settings before messing with it because I was so mad! Also note if you got the scoot used that the prior owner may have the wrong spark plug in it, you need to find a owners manual to find what came in it and what the factory gap was set at, and what heat range the plug is supposed to be. Little things that are wrong cause big problems on a 2 stroke, but when done right they are much more fun than a 4 stroke. That Zuma in my garage calls me but my wife hates "stinky wheels" and I honestly dont want to get caught in the power wars again-been there/done that!
87PGOSTAR50GUY
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Post by 87PGOSTAR50GUY »

sc00ter wrote:It is very hard to help someone tune a carb from a distance, that is why a good local club may come in handy. Do some searching, reach out, offer food/beer if someone replies and get it running. I see you did not do a compression test first, you will just chase your tail in a circle if you have even the smallest leak. I had a main seal start to fail, and I chased the "hang-on" at idle for a whole day before I decided to just check the compression to shut my friend up-he was right though, I had a leak. Replaced the seal and then I had to reset the whole idle side because I didnt write down the base settings before messing with it because I was so mad! Also note if you got the scoot used that the prior owner may have the wrong spark plug in it, you need to find a owners manual to find what came in it and what the factory gap was set at, and what heat range the plug is supposed to be. Little things that are wrong cause big problems on a 2 stroke, but when done right they are much more fun than a 4 stroke. That Zuma in my garage calls me but my wife hates "stinky wheels" and I honestly dont want to get caught in the power wars again-been there/done that!

Mmm well it came originally with a obscelete champion plug they still make plugs for these but would be better to go gapless I have to re pull the top end I believe I hung my first ring or have soft seized.

Sounded like I dropped a bearing but if that was logical it would have stalled and not stayed running. Think its time for a test to see if I'm still clearing the exhaust ports the dish maybe be too much.


If its full blocked then I'll go 40mm 37.4.
sc00ter
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Post by sc00ter »

Why are you messing with the port timing? All that does is ask for a snagged ring. Again, compression test before starting anything else. Are you just trying to get it running, or are you jumping into something bigger without getting the basics taken care of first? Just giving you a heads up-2 strokes are WAY HARDER to tune than a 4 stroke. They are far less forgiving.
87PGOSTAR50GUY
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Posts: 81
Joined: Thu Jan 07, 2016 2:50 am
Location: Seattle, WA

Post by 87PGOSTAR50GUY »

sc00ter wrote:Why are you messing with the port timing? All that does is ask for a snagged ring. Again, compression test before starting anything else. Are you just trying to get it running, or are you jumping into something bigger without getting the basics taken care of first? Just giving you a heads up-2 strokes are WAY HARDER to tune than a 4 stroke. They are far less forgiving.

Nah just want her running perfect nearly bone stock BTW the other piston has with ndpw ports on the opposite side of the arrow, so truthfully if I re install that one Iit will run closer to stock mild very mild domed piston almost a flat top..

4 stroke suck josn at 50cc like tuning a car.
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