99 kx 250

Hi, i recently rebuilt the top and bottom end on my 99 kx 250. I used a Hotrods crank kit, a Wiseco prolite piston, resleeved the cylinder with an L.A. Sleeve as well as replaced all necessary seals and gaskets. The bike was broken in properly but in all gears just before powerband i seem to be getting what sounds like really bad detonation. Once in powerband it's fine. Has anyone experienced this problem before? I checked the powervalve and it seems to be moving freely. I am using Castor 927 premix mixed at 32:1 along with Exxon 93 octane fuel with octane booster. Is it a possibility that the octane is still not high enough? Also when the new sleeve was installed it was bored to fit the piston fairly tightly, i think there was something like .003" clearance so i don't believe it's piston slap. Any help and suggestions will be greatly appreciated, thanks!!!!!!!!!!

wr250f95

octane booster not good.
I would jet it a bit richer, detenation is caused by a lean condition, at least thats how I member it.

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gscx

well you probly shouldnt use octane booster because the oil might not mix with it like the gas will, but what kind of sound does it make, if its a pinging sound right before the powerband but nowhere else your bike is running lean, try rejetting it, but mine makes the smae sound if i give it throttle and hold it open right when the powerband is about hit it will make a plinking noise. but for pre detonation it will alaways ping and it happens especially when a load is put on the engine, take off the top end and check to see if there are pre detonation marks on the head and the piston, they will be little marks aroung the outside of the piston and the head because this is where the compesion is highest, but WR is right if the engine is running lean it will do this because it is running hot, but it has to running pretty lean, look at me and tigs how-tos on how to jet your bike. i dont know how to put up links, but hope this helps and good luck with this problem

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99 kx 250

Cool, thanks guys. Yeah, i was a bit skeptical about the octane booster but didn't have access to any race gas, nearest dealer was 1hr away on a Saturday. I checked the plug, i didn't seem to indicate a lean condition, however i will try running a colder plug as well as pull the head and check for pitting. I'll let you know what happens.

gscx

you should rejet the carburator because putting in a colder plug wont change the air fuel mixture and you bike will still run lean or rich

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gscx

and you can probly use high octane pump gas and youll be fine

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99 kx 250

Cool, thanks gscx. I'll make a run by Cycle gear in the morning and see what they have as far as jetting goes.

tigmaster

how is your cooling system? everything running cool?

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99 kx 250

Well guys, i rejetted the carb, went 1 step colder on the plug and dropped in a gallon of V.P. . Just took her for a run and the noise still persists. My guess is excessive piston to cylinder wall clearance. I'm gonna pull her apart and mic the piston and bore and go from there I appreciate all the help, i'll let you know what i find.

turtlemann14

has it improved any?

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