IS 155 better than standard 158

[BIGMCMACKA]

i recently shattered the arse out of my piston on my 89 kdx 200 luckyly it was only idleing and the engine only stalled so while i have got the engine over at the kawasaki shop getting it repaired i decided to do a few more mods to my bike i have already converted it to a motorcross lookalike with a yz white backguard white backgrounds on the side plates and a race plate and a diskguard i also have a yz 80 muffler on it which would be about 7 inches long which makes it sound really good sort of like a kx,boiseen reeds and a trick pipe although i have not removed the iner layers yet.

anyway my carby has a 155 main jet in it instead of a 158 (standard jet)and if i brought a 158 and put it in would it be any more responsive or is the 155 better

 

[Glitch]

It would make you go too rich from 3/4 to WFO throttle. Causing the engine to lose power and smoke like crazy. Unless you carb was jetted wrong and you were running to lean at high rpm in which case ruining your engine and also causing it to go "bwooooahhhhh" when trying to accelerate. So I would recommend you leave it the same unless your running lean, then go up 1 size main jet until your properly jetted. Do a search on jetting or goto eric gorrs website and look at his jetting tips.
Just my .02
Jim

 

[slcyclerace]

The best thing that you could get for your bike is Eric Gorr's new Motocross and Off-Road Performance Handbook. It will be money well spent. Before doing anything to your bike it's important to know what makes the bike tick. If you understand how your carb works, you can make an informed decision as to what jet you should. Sure you can ask advice from others but there's nothing like having the 1st. hand knowledge to put their ideas to good use.

 

[Canadian Dave]

Jetting doesn't involve looking at just one circuit but rather fine tuning the carb so that all circuits are working properly together. Have a look at the carb tuning section on the JustKDX home page. You should be able to start you quest for a properly tuned carb there.

i also have a yz 80 muffler on it which would be about 7 inches long which makes it sound really good

You'll likely want to reconsider the yz80 silencer. The small core diameter plus its short length will very likely be playing havoc with the timing of pressure waves in the pipe. Though it might sound cool I can't imagine its doing anything but killing power. Check out the Understanding KIPS Valves article on the JustKDX home page. There are a couple links at the beginning of the article that should help explain how the pipe on a two stroke works and the importance of an appropriate silencer, and how silencer selection can impact performance. You might even dicide the silencer is what caused your piston problems in the first place.

David