just rebuilt a kx85. it was done right, not my first 2-stroke. anyway it starts easy, idles all day, runs clean and crisp. Problem is just before it hits its peak power, right where it should really sing, it cuts out and bogs. if you let off a little it stops and runs crisp again. its only the peak. Is it starving for fuel, air, an ignition problem? I didnt mess with any settings at all when rebuilding.

 

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Welcome to KF

Yes, do a plug chop and see what the plug tells you. Most likely a main jet size issue and needle taper, but that is just speculation without knowing what the plug looks like.

 

what is aplub shop

 

plug chop

 

plug chop: The ability to read your plug or plugs at WOT to determine how a main jet, needle, plug, tune and or a synch if there are multiple carbs.

daiksan, if the basic carb setting is good for you on the launch, mid range then at full throttle, run it to full throttle, then kill the engine. Read the plugs. See if you are too lean or rich. The seat of the pants will tell you the low and mid seat of the pants power for the most part.

 

Hey my son's kx 85 2006 is doing the same thing. Did you find the solution to the problem as we are stumped and can not figure it out. Does anyone have a solution.

The plug in ours seems to be burning perfect, we have no starting issues almost always first kick. have noticed when idling when you do crack the throttle it almost sometimes sounds like a rev limiter on the bike, but if you ease nicely on the throttle it will rev up. When driving though we experience the same issue of the bogging when it peaks doesnt matter what gear your in.
If you ease the throttle out it does not seem to do it. We have been trouble shooting this for a while now and no one at the track seems to know even when they hear it happening. would really like a solution anyone please help.

 

I can tell you this much, I took the top end apart and the brand new Pro-X piston had a considerable amount of wear after just a gentle break in. Turns out the "standard bore" piston from Pro-X measures just slightly smaller than a stock piston.???? anyway, I installed a factory Kawasaki piston and the problem was gone. So I guess I must have been losing compression at peak rpm with that small piston. Luckily it only trashed $80 bucks worth of piston and not the jug.

 

Thank You Jake That I will try as It could very well be the same problem my piston show a fair amount of blow- by for how new it is.

Much appreciated.

 

take a look at your reeds if they are not seated compleatly
un screw them and turn them over.run it if that doe's the trick
get a new set of reeds.if what your saying is it acts like a rev limitter it
is consistant with reeds not seeting.