Hello I'm new to this forum and hope it brings me alot of help. Anyhow I have a 89 lt250r, bored .60 over, just rebuilt the top end. Every once in a while it just revs the **** out of it self, even if I'm not on the gas. I noticed once that I kicked the fuel off, but other than that, I don't see why it does it. I know its got gas, and I know that when something is running out of gas it starts to rev up but this thing goes wide open. The only way to kill it is 5th gear and brakes, turning of the key and kill switch, and it will keep running when this is happening. I wonder if the adjustable exaust valve has anything to do with it I don't know and really need some help. The last time I went ridding I let a friend on it and it did this around a hairpin turn and he broke his collar bone, I really don't want to break a bone if it can be prevented. Please help, thanks in advance

 

You are probably running lean. Your head and/or base gasket may have an air leak. Check for any exhaust leaks around the exhaust flang. Check to make sure that you don't have an intake leak. My friends blaster had the same symptoms as your quad. His engine got so hot that his spark plug electrode started glowing and wouldn't let the engine die even after he pulled off the spark plug wire. It rev'd to the moon.

JaMeS

 

Definitely check your throttle cable for sure. It may be binding up and sticking. Also, check the carb, especially the carb slide. I have had the stock Mikuni carbs stick on me also due to dirt or trash getting caught in the slide which can be a very dangerous situation, and I switched to Keihin carbs on both of my Quadracers for that reason and for more performance. If neither of those fix the problem, you probably have an air leak somewhere on the motor.
Try starting the quad in neutral and turn the handlebars both ways to full lock and see if the motor revs then. If it does you probably have a cable that is binded. Next, take the carb off and operate the throttle while checking to see if the slide is moving freely. Hopefully that will help find your problem!

 

I know its not the cable because I don't have to touch the gas. It can be at idle for a little bit then all of a sudden rev the **** out of it self. Its a little scary when the dam thing doesnt want to shut off

 

If it's definitely not your cable then it sounds like you have a serious air leak somewhere on the motor. When did you do your last top end??? Check the simple things first like the reed mainflod to make sure there's no hole in it. If not you probably have a bad gasket somewhere else.

 

Ok another question how do i adjust the exaust valve. The last time I did my top end was right before this crap started

 

Did you tighten the head bolts down to suzuki specs? It sounds like you messed up the gaskets when you put the top end on, or you didn't tighten the head bolts down enough. Check for any clogged jets or hoses as that could make the engine rev really high. Right before my friends blaster would run out of gas, it would rev way up.

JaMeS

 

mine did that once i had it idling with the gas off unknowlingly and it reved to about full throttle when it happened i wasnts even near the quad so its no canle issue prolly yours is porbly sucking air fron around the carb or base gasket so get it running let it idle and spray either around the carb boot reeds base gasket but not head if it revs when your spraying either that area has an air leak

 

Wasup? It's definately too lean,clean out the carb,main jet and the pilot jet.Check the air/fuel screw on the side of the carb and the clip position on the needle,lower it to richen it up,also the float's could be sticking not alowing fuel to enter the float bowl and like the other's have said check for air leak's sucking air will cause it to rev.Oh yeah you don't have to stall it in 5th gear to shut it off when it rev's up,simply hit the kill switch and goose it,I know it sound's dumb but it work's and never pull start your quad you'll end up damaging the tran's......Zilla