Never ending tuning thread

[Smellybumlove]

nothing but headaches with this tuning nonsense, in some ways i wish i just left it with the rebuild and exhaust!.
but hopefully all my experimenting will benefit you guys!
i installed the 28mm keihin flatside with loads of troubles , i had to have it setup and rejetted 3 times before its even rideable, the first time it would idle at 6000rpm after opening the throttle for about 1 minute at the lights and die if you gave it full throttle from the lights.

2nd time it would ride like crap at anything other than full throttle and be impossible to ride until it was boiling hot.......

now this 3rd time its rideable but still takes too long for it to be rideable from cold, it makes a horrible missfiring ping noise until its hot and anything other than 75%-100% throttle opening does the same thing. Also the most annoying thing is that if you crack it open from a standstill it stutters and coughs for a good 2 seconds before buggering off, thing is if your crawling along at 1mph it takes off like sh!t off a shovel a hell of alot quicker.

any ideas?

to keep you up to date with whats been done heres a list....

engine rebuild with port enlarging and polishing along with a 53.5mm piston

high power coils and spark thingy

BWS V8 exhaust system

uprated variator

extremly hard clutch springs

now its on 7G rollers 10k rpm

quick action throttle

pwk28 flatside carb along with the required manifold and original air filter (aftermarket are too noisy and make no power)

ok thats it for engine mods

im thinking that maybe the carb is too big and if i enlarge the piston to say 56mm it might help with it dealing with the extra fuel?.

[BGK]

Enlarging the piston to match the carb is a bit of 'the cart before the horse'.

I don't think the carb is too large, but being large it will be much harder to tune. With that displacement it would seem like that variator weight would be OK. But the symptoms are that of too low of a variator weight. Dropping it 0.5 gr at a time will get you into the right range. But it could also be that you are just making no power in the lower rpms so you could need heavier clutch springs. I'm talking about the little springs, not the bigger contrast spring. You should have a heavier contrast spring as well. That is a bit analogous to lighter weights so if you don't have one, you could try that first before lowering weights.

I think using a smaller carb like a dellorto 21mm would make it much easier to tune.

[Smellybumlove]

yeah i got the heavy clutch springs, and i mean heavy as you have to scream her to get her off the mark.

i got her revving to around 10k but its not making anymore power, regardless thats not the actual problem, its the nasty pinging going nowhere at below full throttle.
might have to switch to a 22 or a 24, but im still not happy as the BWS use the 28mm no problems .

so are you saying that boring he rout to 56mm wont take away the problem?

[BGK]

Yes, boring it out won't take away the problems.

With the changes in port timing your ignition timing will also likely need to be changed. I'd increase the advance about 2 degrees at a time and see if that improves anything. But before doing that. Throw in some 5 gram weights and see how it feels. It's much easier that changing the ignition timing.

Also, that carburetor may be OK for other applications but maybe now you are experiencing the difference between the two motors beyond the engine cases. That carb is much much more adjustable. If you are an expert tuner then that gives you more freedom to dial it in correctly. But while learning to jet correctly for all the ranges of throttle opening it makes it much more difficult. You'll need a range of idle jets and needle tapers to get the entire range correct for any given motor. I like the dellorto carbs because of their typical ease of set up. Keihn and Mikuni carbs mostly come from the factory set up for high performance motors. Dellortos mostly come from the factory destined for scooters! You scooter may have a bunch of nifty new parts on it but it's still in a very low state of tune relative to motocross or grand prix machines.

[Smellybumlove]

thank you, best explanation i have heard for ages!.

i can see where the problem is, its not taken ages to get warm its just riding like crap at anything other than 75%+ and i dont give it that abuse until i feel its warm, of course i never feel as if it does get warm as it rides like crap all the time!.

so it just needs some fine tuning on the jetting AGAIN!

is the ignition behind the plastic fan thing as i saw him doing something behind there, i guess that means i dont need a uprated cdi!.

maybe since the engine was tuned for the stock carb and exhaust, it would help for the intake and exhaust ports to be tuned accordingly?.

[BGK]

reshaping the transfer and exhaust ports is a delicate art. You'll have to adjust jetting and transmission settings again afterwards. It all just depends on what you want.

1) decide what you want
-loud fast stoplight racer?
-quiet reliable scooter, but a bit faster?
2) decide on cylinder, exhaust and carb considering your answer to #1
3) combine and fine tune parts for smooth running at all RPM ranges.
4) adjust cvt to suit the power output you've built.
5) adjust clutch engagement speed for desired take off performance.

Moving from one step to the next without completing the previous one will end up with you chasing your tail.

But a bunch of jets and needles and read some books or websites on 2 stroke carb tuning. Once that's dialed in, set up the variator/rear pulley. Then the clutch. Out of order and you'll waste time and money.

[Smellybumlove]

1)well this project has always been about being as mental as possible, thats what it is in the first place anyway!.
2) the exhaust is designed for peak power only which is why i went for the 28mm flatside.
3) this is the thing thats troubling so far, will give it one more go tomorrow, im being told this is as good as it can be but i just cant believe that!.
4) the cvt was/is adjusted for crazy bull accelration, but now since its so powerfull it needs to be toned down so will change the big spring on the back.
5) clutch is set for high rpm deployment for the fact that its a 2stroke and makes no torque low down anyway!.

i have done things in a progressive manner but i didnt think about what would happen when i added this carb, it was all set for the original carb so now im having to reset it for the flatside

[Smellybumlove]

FIXED!

didnt need rejetting just a screwdriver and some adjustments, its perfect now and a absolute BEAST!.
it rides like a fuel injected bike, no bog down just snap and go, top speed is over 60mph and it wheelies from 0-15mph without leaning back....

loving every minute of it, mpg has dropped a fair bit though so probably 45-50ish but who cares .

[goatlover]

http://themotorcycleshopsa.com/

if you look at this page Scroll down until you see the rattler. they installed the prima pipe and a 19mm carb. when I called them they said this was best set up they found. they also set up the rollers but I forgot what weights..

it might help.