rm 250 backfires,wont run

[dave t]

i have an 89 rm 250 that wont start,am new to 2 strokes.all the bike will do is a huge backfire about every 10 kicks or so.flywheel key and mag looks fine to me,got fat spark.i have no idea how to check timing on this bike,any advice would be greatly appreciated.would reeds cause this problem?the guy i got it from said it just died one day,never ran since.thanx

 

[wasted]

it could be the reeds, its worth checking out anyway... but my brothers quadracer(which has basically a late 80's rm250 motor in it) did the same thing that you described, it just died while he was going down the trail and wouldnt start unless we pull-started it, all it would do if you kicked it was backfire every so many kicks, we dumped a little 2-stroke oil down the plug hole to try to up the compression and it almost fired enough to start, but wouldnt...

not that this is what is wrong with yours, but his had developed an air leak between the rubber intake boot and the reed cage which leaned it out enough to fry the rings, which dropped the compression enough that it wouldnt start...

so I would say if the reeds are good run a compression test and see what that is, I'll bet it doesnt have enough compression...

 

[Chief]

I have an '01, the only time it backfired is when I melted the rings and scored the cylinder. If you can't find anything else wrong, it might be worth taking the top end off for inspection. Maybe you want to have the new parts ready for a rebuild if it is due anyway.

For piston, ring(s), topend bushing and new gasket set you are looking at about 150 dollars plus or minus. It is a relatively simple procedure and if you get someone with experience to help you, it should only take a few hours or less.

Good Luck!!!

Joe Chief

 

[dave t]

it seems to have good compression when kicked over,im a pretty good mechanic,just never worked on 2 strokes much,so rebuild wont be too hard for me to fgure out.dont have a compression guage but it sure feels like it has nuff to run.im going to start taking it apart tonite,at least look at the reeds and intake.thanx guys

 

[dave t]

oh, also on the side of the cyl/head it has some kind ofvalve or some thing,i have no idea what it is,it turns pretty easy

 

[adam.thorsbakken]

That thing on the side is a powervalve, it may be out of adjustment or worn out also, The powervalve opens and allows the engine to gain RPMs faster, if it is leaking compression, that could be a possible cause to your problem, You need to acquire a compression tester and a manual for your bike, then the book will tell you how to troubleshoot your problem

 

[wasted]

that "valve" is the return spring tension adjuster for the exhaust valve and I doubt has anything to do with your bike not starting...
just because it still has compression doesnt mean there is enough there to start it, if I remember right my brothers quadracer called for around 120...
if the reeds are good try pouring a little 2-stroke oil down the plug hole and kicking it over, if it still doesnt start try pull starting it, if it starts and runs then its more than likely bad compression/burnt rings... I wouldnt run it long though, just enough to see what kind of noises it makes and if it has a small airleak...
it very well could have developed a small airleak and running it wide open would have leaned it out to the point that the rings burnt...
if it was me, and the reeds checked out good, I would probably just tear it down anyway as opposed to running it anymore and taking the chance of damaging the cylinder any more, it probably needs a rebuild anyway, and an exhaust valve cleaning...

 

[dave t]

reeds look fine,i can move the rod side to side with my finger tho.the intake had silicone for a gasket,guess that was a bad idea..............