RM250 Went full blast without twisting throttle while riding.

[Mudd Hammer]

I have a 89 rm250 and while i was riding the thing went crazy out of the blue while i was going down my street like i had the throttle way open but it was closed. the thing bucked me off and ran for like30 seconds then shut off. When i started it back up it hd blown a head gasket? Sucking in coolant, looked like a stunt plane so much smoke came out. I took the top end apart, replaced the gaskets, cleaned the carb, reset the idle, fuel air screw. When i started it, it went crazy again. I cant figure out what the hell is wrong. I reset the needle and cleaned everything. It ran great before this craziness happened, HELP!!!!!!!!!!!!!!!!

 

[SpeedyManiac]

Air leak. Check the boot between the carb and the engine for cracks.

 

[elcamino12sec]

First thing I would do is replace the throttle cable. The bike is almost 20 years old so thats a good idea anyway and rules out the throttle cable sticking being a possible problem. Second, check for an air leak. Common areas are rubber intake boots and crank seals. A really wore out throttle slide can cause air leaks too.

 

[Patman]

Crank seal?

 

[Mudd Hammer]

wouldnt a crank seal be burning a ton of smoke thoough?

 

[RM_guy]

Not the right side crank seal.

 

[snowskater101]

were you putting around then without giving it that much gas it revved up or were you pinning it and it didnt go back down when you let off the throttle?

did it maybe run out of gas?

 

[RM85rider123]

the same EXACT thing happened to my friends little pit bike, the part of the throttle that sits in the engine probably gummed up, try starting it without giving it throttle when kicking, thats what my friend did, and he was good for the rest of the day.

 

[robbieisurfriend]

Sounds to me like you were getting too much air. I learned just the other day (the hard way) that running a 2 stroke down to the very bottom of the tank will cause them to do that. The extra air leans out the mixture. Most likely you have an ail leak somewhere in/near the carb. Good luck wish I could be of more help.

 

[Rotorranch]

You did have the gas turned on, right? :whoa:

I would look at the carb first. It may be stuck open. If not that, air leaks would be next. :nod:

I don't understand how a runaway blew the head gasket, though. :coocoo:

Rotor

 

[Mudd Hammer]

Yea we took aprt the carb, cleaned everything and reseated the needle. The bowl was leaking a little but i used a thin layer of tube gasket with my finger and tightened everything up real good. As far as i can see there are no leaks. I turned in the fuel air screw 1 turn to richen it up and backed out the idle screw. We started it up and it wasnt reving high but it sounded different. It was burning a brownish tint out the exhaust. I havent had a chance to really blast it out yet but i will be doing that tonight.

 

[Rotorranch]

Yea we took aprt the carb, cleaned everything and reseated the needle. The bowl was leaking a little but i used a thin layer of tube gasket with my finger and tightened everything up real good. As far as i can see there are no leaks. I turned in the fuel air screw 1 turn to richen it up and backed out the idle screw. We started it up and it wasnt reving high but it sounded different. It was burning a brownish tint out the exhaust. I havent had a chance to really blast it out yet but i will be doing that tonight.

You really shouldn't use any sealers, or "tube gasket" anywhere in a fuel system. Especially any silicone rtv sealer. It is allergic to fuel. It tends to "travel", and get stuck in jets, and other orifices where it shouldn't be.

Rotor

 

[125rmcrazy]

yeah running the tank dry will do that! i hada 85 yz 250 and had it happen to me in a wheelie in 4th gear. on pavement...t-shirt and jeans on. not pretty.....lol.

 

[kawirider88]

check your reeds??

 

[2strokerfun]

I don't understand how a runaway blew the head gasket, though. :coocoo:

Rotor

Weakest link in the chain, maybe?? I've had them run away where they start self igniting and grounding the spark plug won't even stop them. Had to stomp it in gear and pop the clutch. Mine spun the flywheel off the crankshaft. Made a hell of a racket.