Jetting for high compression piston

My bike is all stock. The previous owner put in a high compression piston when he rebuilt it. It has a surging at cruise throttle.

I have tried every needle position and it runs the same at cruise throttle with a constant surging. The bike runs perfect in all other throttle conditions like rolling on and wide open throttle.

What specifically needs to be changed in the jetting to accommodate a high compression piston on an otherwise completely stock bike?


what is the jetting at now and what has been done to the bike?what elevation are you at?

If it's otherwise completely stock I would suggest you install a JD jet kit ....settings for less then 3000ft listed below ..

#155 main jet

jd blue needle

clip 4

22.5 pilot jet with extended screw or 25 pilot jet with stock screw

2.75 turns

3x3 mod

Right now the jetting is back to stock. When I bought the bike it had the Dyno jet kit in there. I tried all the variations with it and there was no change in the surging.

The elevation here is 600 feet.

See my thread from August 2010 to see all the different things I tried in order to fix this situation.

I ran the DJ kit with the stock CV slide spring and that worked good. I think the softer DJ spring let the slide rise quicker than desirable when cranking the throttle. The more tapered DJ needle woke it up though.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now