I have an 87 TRX250X that has a problem. It runs perfect at idle to about half throttle all day long. Over half throttle to full throttle it sputters and blows slight black smoke until it dies. I got a new carb from a 2002 300EX and put it on thinking there was a problem with the original carb. Same thing. I bought a complete electronics package (CDI, regulator, coil) No difference at all. I am out of ideas. The top end is new and tight. If I tilt the quad back onto the grab bar, fuel pours from the overflow. I will pull the carb and check the float level and jet sizes. Next a stick of dynamite. Anyone heard of this?[img]i/expressions/face-icon-small-disgusted.gif[/img]

 

ya mine did the same thing man!! i just went all out and did everything to the engine look at my profile and see what im talking about.. well all i can say is get a BRAND NEW! carb thats the only way its going to fix it i bought mine from carb parts wearhouse in Ohio they are the best IMO they send ya everything and tell ya what all you need.. with extra jets incase they didnt do it right from the begining.. they usually get it right but they were one step down for my bike well hope this helps

 

You are to rich on the jetting. With a 300ex carb, if the rest is stock use a 122 main jet. If you have aftermarket exhaust and opened the air box, you will want a 132 main or so.

My quads will have gas running out the over flow if stood on the grab bar, that is what happens.

 

Did this start to happen after you got the new top end? the reason I saying this is the same thing happened to me I did the same thing you did bought all those parts you bought too and it still didnt run right. well this is what I found out. The timing was off, the timing chain was put on one tooth off it was not alligned at top dead center. after that was fixed it solved all my problems and now my 250x runs great. hope this helps.

 

OK, I dropped the needle down (clip up) as far as I could go. Seems like it revs quicker, but bogs instantly if throttled too quickly. It runs absolutely perfect, never misses a beat to about half throttle. Sometimes it will take full throttle for a second or two, but then starts breaking up. Cam timing right on. Stator and pickup ohm out like they should. I am going to try to go down on my main jet from 125 to 120 and put the needle back in the middle. Thanks for all of the support!

 

I did'nt have these problems when I rebuilt my 1st 250x "stock" ,but with a k+n air filter and a cobra exaust I put a 132 mainjet in, stock I think was 125. But yours does sound too rich on the high side. Make sure your air filter is clean also because that can sometimes cause this. Try taking the filter off as well to see if it still does this.