Almost blew up my rm 250!

[markyb]

I have a 1990 rm 250 and was taking it for a little spin the other day and the throttle or something got stuck wide open. I had the clutch pulled in so I got it into neutral but it was at about 10000 rpm. The kill switch was not shuting it down, I kept hitting the throttle to make it stop. After about 10 or 20 seconds it quit. I let it sit for a few days and then took the carb off and checked everything out. The needle and throttle body seemed fine and it all looked in working order. I put everthing back together and took it out for ride. I ran it slow in first gear and then pulled it into the driveway and slowly started to give it gas in neutral. Same thing happened. It started to rev on its own almost and would not go back down. Kill switch would not work. The throttle at the bars is not sticking. I can not explain this, any ideas. I dont want to try it again until I fix something or I am afraid it is going to blow the engine. Need some serious help!

 

[Chili]

Look for an air leak. Have you done any work to it recently, removed the carb etc?

 

[jason33]

air leak- or something cloggin up the fuel valve-
if its a air leak- check the ignition side seal-

 

[markyb]

I've never removed the carb. The previous owner had it ported and jetted about three weeks before I bought it. It has always stuck a little, but never that bad. where would air be coming in at? around the carb boot on the engine side? Is that what you mean by ignition side seal? If so, how do I fix it and why would it happen only when I am reving up past about half throttle?

 

[markyb]

how do I check for leaks?

 

[jason33]

you can look at the ignition side seal to see if its bad- its under the stater,and magneto-- or it could be a air leak in the carb boot itself- or the base gasket- but you should be able to see and hear it
usually after a top end job the ignition side seal will blow -- this sound like what happened-- quick fix-10 dollar seal
should pop out the left side put in a new one-


there is a leak down test kit you can get - you take off the carb and ex pipe plug them up with the plugs in the kit- a air pump attaches in the spark plug hole and you pump a certain amount of air in the cyl - let set an measure how long,and how much is leaked out

 

[rickyd]

If it ever happens again, cover the exhaust. The spent fumes will kill the engine..

 

[markyb]

thanks for the help. I am new at doing my own work so I need a little more assistance. To replace the ignition side seal I need to remove the left side crank case and then remove the magneto and stater, Correct? I have a clymer manual and I do not see anything about an ignition side seal so I am a little confussed. Thanks for the help.

 

[Someone]

I've had the throttle cable get frayed and stick on me when I had my 2001 YZ 250. I hit the kill switch and it did nothing, then I smacked a tree. This was BEFORE there was a recall on the throttle cable guide in the throttle housing.

You would think they could engineer a kill switch that absolutely will not allow current to flow when used.