Hi everyone. A friend of mine just boought a 99' 300 ex and now it's started to miss at higher rpm's. It seems to be running hotter than normal as well. Any suggestions? Timing? Carb? Ignition? Neither of us is a master mechanic by any means so any input is welcome. THANKS!!!

 

If it's missing at high rpm's i would say check the jetting maybe it running a tad rich. You can just look at the spark plug to see whether its lean or rich. If its not that i would say its the ignition system. Mine didi this a little bit ago, and i just closed the spark plug gap alittle. I went form a .020 to a .016. It solved my problem. As for running hotter that is due to soemthing being off, so as a precaution i owuld check your timing as well. I would reccommend going and buying a manual for it, the clymers have quite a bit of info in them that may help you.

 

Thanks. We changed the plug and it helped some but the issue still exists. We'll try regapping it. Thanks for the advice. At one point it had an aftermarket exhaust but the seller took it off and put the stock pipe back on. We were wondering if maybe the carb was jetted for the aftermarket pipe and now with the stock pipe back on it's causing problems. AS far as the overheating i agree with you on the timing. How difficult is it to check and or adjust?

 

If there was an aftermarket pipe then the jetting could very well be off. I would try and maybe go down on your main jet size, or lean it out with the needle clip. Just play with it, but watch the plug, if it looks really grey than you're running lean and could burn the motor. You want a nice tan color. But i wouldn't play with the timing until you get the jetting setup and the miss gone. It could just be do to the fact that its missing. Did the missing start all of a sudden or did it miss when he bought it?

 

It's been missing since he bought it. I think the guy tried to pull one over on him. Had him pick it up at night in a parking lot which obviously limited the test ride. Supposedly the guy has the aftermarket exhaust and is willing to sell for $70 so maybe we'll try putting it on and see what happens. I'll keep you updated. Thanks for the input on the plug!

 

The stock ekhaust will be fine if you don't want to spend the money. Just move the needle clip a couple of notches up and see if that help. If its still rich go to your local Shop and get a smaller jet, they're like $3. If that still doesn't help, i would call and see if hes willing to give you any information. But if your friend has the money then i would try putting the pipe and muffler back on before you go through the hassles of rejetting.