Lean surge or detonation????

ok here is the deal. i cant figure out if what my bike is doing is a lean surge or mild detonation? i am also not sure if this is a fuel issue or jetting. here is my setup--

2008 yz250 with eric gorr 295 kit head cut for pump gas

klotz super techni plate 32:1 / 93 pump gas

#8 slide / jd red needle third clip

172 main

50 pilot

3/4 turns out on air screw

timing .007 (stock)

0-2500 ft

2 weeks ago we were in the mountains and the bike ran very well- 2500 ft low humidity. only surged a couple time when it got really hot in the tight stuff but not bad.

rode the bike this weekend backhome - sea level 90+ degrees high humidity. i have a surge right @ 1/8 throttle. it gets worse as the bike gets hotter. seems like a lean condition but why would that get worse when its hotter with higher humidity? i have checked for air leaks and it is good to go. crank seals are also good to go. i tried going up one on the pilot and it did not cure it. it just felt rich right off idle but still had the surge.

i spoke with eric gorr and he said that even though the head was cut for pump gas it may be needing a little bump in octane. he suggested klotz octane booster! honestly for the cost of that i may as well run 50/50 mix of 110/93. any thoughts?? i also tried dropping the needle one more clip and it did not cure it.

because it gets worse with heat i want to think it is detonation/pre ignition. oh and my plug looks perfect- coffee brown. any help is much apprieciated....tired of chasing my tail on this.

Have you tried retarding your timing a degree or two?

Have you tried retarding your timing a degree or two?

it is set to stock right now. i am going to try that next. However, i just wanted to see what everybody thought as far as detonation vs lean jetting.

Race gas will help, that is easiest fix. #7 slide or +1 in main might be other options

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