1999 KX250 hard to start

[Assassin5150]

I just purchased a 1999 kx250 about a month ago. First few time riding it had no problems starting it, now it hit and miss sometimes it will start in a few kicks or i will have to push start it. when running it seems to run very strong. Last time out riding, it did seem to smoke a little, but I was riding trails with my son and was putting around in first and second gear. when I got out in the open I got on it pretty good which seemed to clear up the smoking issue. I figured it was unburned oil in the exhaust. Oil level seems to be goog and not leaking into the cylinder. I have checked the spark plug it's not wet or fouled cleaned the air filter which gave it better throttle response. I plan on rebuilding the top end soon and replacing the reeds at the same time. should I start trouble shooting it at the carb ie (cleaning and new jets) it has stock exhaust and pc silencer and using a 32:1 fuel mixture. I am also questioning the fuel. The station I buy it from says it has no ethanol in it's fuel. From what I have herd ethanol enriched fuel will cause starting problems. So I might try another fuel station.

[MoToMaStR]

Summer time is comming, its probably in need of slight to mild jetting. Everything will have an effect on your jetting, and 2 strokes happen to be pretty sensitive to changes in altitude, air temp, humidity. Catch my drift? You might be able to get away with dropping your main jet 1 size down or leaner 1 size. Its about a 3 dollar fix and you should be able to pull the jet with out taking your carb off. Turn off your fuel, Loosen the steel cinch bands around your intake boot and air boot, rotate your carb towards you, and remove the drain plug at the bottom of your fuel bowl on your carb. Have a rage or something to catch the spilled fuel. Now look in there, and take a 6mm socket and you can remove your main jet. PRESTO! hope that helps dude. good luck

[Assassin5150]

I plan on just pulling the carb and giving it a good once over. Could the float be part of the problem? If so any help on adjusting the float? The guy I bought it from didn't know anything about the bike. His neighbor did all the maintenance on it. I recall him saying that his neighbor did something to the carb because the bike was too much for him to handle, but he didn't know what he did. Have no idea what he ment. Maybe he adjusted the jet needle. As far as jets go should I replace the jets with the factory size? Main jet being #158 and pilot jet being #45. As far as I can tell in the parts catalog those are factory sizes all other jet sizes are shown as optional. Sould I replace the power jet?

[MoToMaStR]

Its one of those things that you find of have to be there to diagnose, however.... Judging by the symptoms you've described suggest a rich running condition. I would take out your plug and inspect it. It should be a mocha tan or brownish. not black and oily. If it is black and oily that definatly means your running TOO RICH!! If your plug is white and ashed over, its too lean and you will surely experience piston/cylinder damage.

*you said the previous owners neighbor did something to tame the power by playing with the carb.... I dont know why anybody would do that, but richening the air:fuel mixture will make the engine "rev slower" and "less violently". Isn't that the whole reason we all love 2 strokes? I say, if you cant handle getting kicked in the face by a steep powerband, then get off and ride a 4 stroke.


Sounds to me like that dude cranked the air screw in a bit to make the bike more of a sissy girly trail riddin putt-putt mobile. Do yourself a favor and read over spankys jetting guide. Its a stickey at the top of this forum. That'll probably answer about 95% of your questions and concerns.

Im almost positive its going to be playing with your air screw, or dropping 1 size on your main jet, and playing with the air screw. Later dude.