Should i rejet?

[Honda2000]

I am planning on having a friend put a standard bore wiseco 11:1 hi comp piston on my wheller. I am wondering if i will need to rejet. I live in the middle of kansas if that helps at all. ALso i am wondering if it would be better to run race fuel or just premium. I guess i might have to wait and see which fuel to run after the piston is installed, "i am not for sure" this is my first atv. thanks ahead of time for the advice!!

[GPracer2500]

If the only thing changed is the compression ratio of the piston then a jetting change should not be needed.

Note: If anything you'd actually have to lean the jetting to maintain an ideal mixture when just adding a higher compression piston. This might sound strange, but the reason is because a more tightly compressed air/fuel mixture burns more effeciently. Higher compression makes better use of the available fuel so the required quantity can go down. But in this case the effect on jetting is so small that you don't need to be concerned.

As far as racing fuel--it depends. Is the cam stock? If so there's a chance you'll be pushing the limits of getting away with premium pump. Just be on the lookout for pinging or knocking sounds coming from your engine--especially under high heat, very high load, lower/mid rpm operation. Those sounds signal that detonation is taking place. If you've got an aftermarket CDI with extra ignition advance that will make deto even more likely. But there are so many factors that contribute to the onset of deto that it's very hard to say what your engine's octane requirement will be.

[Honda2000]

oh sorry i forgot to ad i have a slip on, K&N, hotcam stg 2, and a rev box.

[krt400ex]

Originally posted by Honda2000
oh sorry i forgot to ad i have a slip on, K&N, hotcam stg 2, and a rev box.


haha, oh well everybody forgets sometimes. no, u shouldn't have to re-jet, but like gpracer said, u might have to run race gas. a 50/50 mix would be fine

[Honda2000]

I was planning on mixxing 50/50. Also do you think i need to upgrade my clutch? thanks

[krt400ex]

i would do stiffer clutch springs. they r only like $10 and they will almost completely assure that ur clutch won't slip. that's just me though. i would do it with just a pipe.

[Honda2000]

ru shure that it won't help to rejet? the guy i got the piston from said that he ran a 165 or so and it ran a lot better. WOuld it be a waist of time to try a bigger main Jet? thanks

[GPracer2500]

Originally posted by Honda2000
ru shure that it won't help to rejet? the guy i got the piston from said that he ran a 165 or so and it ran a lot better. WOuld it be a waist of time to try a bigger main Jet? thanks

If your jetting isn't correct then YES, fixing the jetting so it's right is the thing to do. But if your jetting IS correct for whatever mods you currently have, and then you install a higher compression piston of the same displacement (and that's the only thing you change), you shouldn't need to rejet.

It's almost never a waste of time to experiment with jetting when you suspect something isn't right or could be better. But don't fall victim to the tendency to believe that bigger jets = bigger power. If you find an increase in performance with fatter jetting then you would have found the same relative increase had you rejetted before the piston.

[Honda2000]

thanks for the info i am going to buy a few bigger jets and experiment