1992 KDx 200 surges above 1/2 throttle

[jreibson]

I am restoring a neglected and worn 1992 KDX 200. I replaced a bunch of stuff and can finally ride it. When I'm riding it and get the RPM's above 1/2 throttle the engine starts to rev up and down in a cyclical manner. It sounds like I'm hitting the kill switch for a fraction of a second then letting up on the switch and then hitting it again and again. I've replaced the air filter and the air intake manifold. The reed cage and reed valves look fine. I've cleaned the carb, installed new stock jets, set the air screw at the stock setting and tried all of the slide positions on the 1172 needle. I tried my best to measure the cylinder bore and the piston OD and they seem to be in spec. I compared the operation of the power valve in my bike to a friends KDX 200 and it seems to be working fine. I simply don't know what else to try and it's driving me crazy.
The only other issue this bike has is a slight oil leak in the area behind the stator plate in one of the three depressions where the aluminum and steel heat up at different rates.

If anyone has an idea about the surging issue I'd love to hear it.
Thanks.
John

[Postigo]

Hi, sounds like a lean condition to me. Check the inline filter located inside the tank over the petcock because they tend to collect debris of all kind and can cause a lean condition by restricting the gas flow at hight RPM. The other chance can be the stator oil leak and can be cleaned and sealed with some JB weld. Hope this helps

[bufftester]

YOu have a fuel delivery issue, so start at the beginning and work through. As Postigo said, make sure you have a clean tank/petcock/filter, no kinks in the fuel line. Clean the carb....then clean it again. Fresh fuel, new plug, clean filter, repack silencer, make sure all rubber intake tract boots (from air box to carb and from carb to head) are good. Then follow the jetting guide step by step. You'll find a common theme on these bikes. Jetting is everything. Decide on a premix ratio and oil and stick with it. If you change anything in the intake/engine/exhaust you'll need to rejet.

[jreibson]

Thanks bufftester and Postigo. I'll fix the stator leak with some JB Weld and then start at the tank screen and work my way through the fuel system and check for air leaks at the same time. After that I'll put in fresh fuel (32:1 (Motul)) and move on to jetting. I've only ridden about 6 hours since I repacked the silencer so I think that should be OK. My 16 year old son and I really appreciate your help with this project.