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Hi Guys, got a performance exhaust and cone filter today for a 156FMI (ohc) engine, received two 105 jets, opened the carb up and replace main jet 94.5 with the 105. Got my colortune out, tweaked the mixture, I have a blue flame on idle or a set rpm, on acceleration flame color is yellow, every seems to work okay. But as soon as I take it out onto the road, at low rpm (<4000) it works fine anything mid or high end it struggles and stutters.
Any ideas, advice or help?
Air filter?
I tried standard back box, foam and cone air filter, all with identical results. Any other ideas? Also on the carb you have 1 line for fuel, a return (vacuum) and a third pipe, whats the third pipe for?
Downsizing main jet?
Does the 3rd pipe connect to the bottom of the carb? If it does that is the drain pipe which drains off excess fuel from the float bowl, the other end dosen't need to connect to anything just tuck it away somewhere. As for your performance problem make sure that you don't have any intake leaks, the orings may be worn and need replacing. You can check for leaks by spraying a combustible substance (brake cleaner, wd40, etc) around the intake duct with the engine running and see if the idle speed changes at all, don't get any near the filter as that will give you false results. Otherwise play around with the needle position on the throttle slide and/or get a smaller main jet.
Remember that a colourtune (or any other fuel/air mixture testing equipment) won't be very accurate with the bike at a standstill; you can only test it accurately with some load on the engine. A spark plug test while going up hill would probably be better.
Thanks for the help, turns out the stock nuts and the studs where loose, so I redone the tubbish stud with some locktight and replaced the nuts with nyloc ones.
For a performance exhaust and cone filter does a 105 Jet sound right or should I look at a 110? I will be looking at the spark plug to see some results.
The two mods have vastly improved the bike especially midrange, my only problem is it struggles between 8k and beyond in revs, I'm not the lightest fairy though at 17st (110kg), any ideas?
Stock sprockets still a 15T, engines only done 500km as well and I never knew colortune had to be under load, I've worked with cars alot, but most of it being modern injection, via OBD2 and Vag-Com.
I'd say a 110 main jet for cone filter and exhaust, they are only a couple of quid each though so it wouldn't hurt to experment. A bigger main jet should help with the really high RPMs but you don't want your engine to explode do you? Get a 16 tooth front sprocket and you will be able to go faster with less revs.
Colortune dosen't nessesairly have to be done under load I was just saying that the readings could be off a bit with no engine load. Professional tune ups are done with a dyno to add load and measure horsepower but that shit's expensive.