I have a fairly low hour 1984 XR 250 (still on the stock chain and sprockets).  Took it out for a ride today and it started running lik crap, backfiring, belching black smoke, cutting out and refusing to rev very high. Managed to limp it 12 miles back to the truck this way, not fun but better than walking.

From what I have read on the XR 600 forum, this sounds like a stator problem (stator biting the dust and not proving a strong spark). However, before I start wantonly spending money on the bike, I want to see if I can make sure the stator is the issue. The bike ran fine on its last outing (last week), though I did get it fairly hot on a hill climb. It ran fine after the hil, went another 10 miles back to the truck, got parked and sat until today. my thought is that the heat pushed the 28 year old stator over the edge. This is a good bike that is worth fixing, just want to make sure I am going in the right direction.

Any thoughts would be appreciated

thanks

Going after intermittent electrical problems are never easy to diagnose.  I would clean the carb first ( because it won't cost anything ), making sure to use a piece of bread wire to clean out the jets.

Even when you blow cleaner and air through a pilot jet, they just will not get the deposit film out unless you pass a wire through it.

Perc

I agree with Perc82. The carb is what I'd be looking at, not the stator.

How old is the fuel? Check for water contamination.

Do a good carb cleaning.

Not saying this is what your problem is but you said you ran it hot; next time you open the engine up, have a look at the cylinder head between the spark plug hole and valve seats for any cracks.

Pop a new spark plug in too, as a matter of course with this sort of fault.

I tried a new plug and gave the carbs a good cleaning. neither resulted in any change. bike still starts right up, runs OKat low rpm an then coughs, splutters and backfires at anything more than a few thousand rpm above idle. My gut feeling is still that this is an electrical problem.

Could be the Stator,,could also be the ignition coil. Normal symptoms of a stuffed coil is the bike starts and runs fine at low revs but as the engine heats and the coils electrics work harder the bike does as yours is doing,,farting,,can't hold revs,,ie a lot of throttle work needed to keep it running..If you let it cool the bike will appear normal again until she's restarted and gets up to stress levels once more,,No guarantees but I'd replace it first then look at the stator, or check the stator and if it looks ok go for the coil..

Stator,,May be a loose wire or a badly held together wire inside the cover or somewhere on the wiring between the connection of the Red/Black wire to the loom and the actual stator windings..Any sort of half held together Red/Black (ignition wire) down there can vibrate about causing an intermittent short..Eyeometer that wire all the way to the stator windings for a bad connection..An ohm meter is not suitable for the check as if the wires still held together by just a strand of wire it'll say it's good,,eyeometer is the proper way to check it. You may have to cut back some external plastic covering to check the wire thoroughly..not the plastic over the actual wire,,the other outer sheathing..

Edited by Horri, 29 May 2012 - 12:41 PM.

I had an 84 XR250R that did the same thing, it was a small bead of water in one carb blocking the main jet.
Do the easy things first, drain and flush each carb and then retest.
I found it was easiest (relative term) to remove the carbs out the left side still attached to the manifold.

looks like the ignition coil was indeed the issue. New one arrived today, I just installed and fired the bike up. Rode the bike around a bit to get it warm and it now runs just fine. Much more useful object now that it revs past a few thousand RPM!