I have been having some trouble with my 86 250R in that at in the power band it sputters. It is not very bad but I know it should be smoother. I have tried changing the main jet but it did not make much difference in the sputtering. I started out with a 152 and went up as high as 168 and as low as 140 and it was not very noticable. I checked the compression cold and it was 120 and hot was 125. It is stock except for the P. T. pipe. Is this comression to low or alright? I would appreciate any helpful input.
Thanks.

 

I am not a mechanic, but 125lbs seems pretty low to me. I think factory is about 170lbs, and I know that my race bike is up at 250lbs of compression. I do not know if that is causing the sputtering, but it is a definite possibility.

 

If compression gets too low, that could happen. The thing with a 2-stroke is that maintenance is the key. They are cheap to work on, and if properly maintained, you can make the piston and bore last a long time. Once you start notecing less compression by feel of the kick starter and can hear it loose it faster than normal and also hear extra rattling noise in the top-end , it's time for new rings and a hone job (usually if changed soon enough), which is cheap. Most people seem to wait too long, that's when you start either blowing it up or are just stuck boring it out due to lack of maintenance. I'm on my 3rd set of rings in a little over a year and I'm still on the stock bore. That may sound like allot, but not considering it's a full race 330 and I ride it all the time for both trails and racing, and its only rings and a base gasket, so it's cheap preventative maintenance, and it's also alwys running very strong. I actually just got done checking it out before I raced this last weekend, and I am going to put a new piston in this spring, but it won't need bored at all. I did go ahead and hone the cylinder to reseat the rings, and it has all it's compression.

That's my experience anyway.

Sickman

 

You didn't say if if this was a new problem, or a recurring one, but you might try checking the needle in the carb before tearing it down. This will make it sputter, if set too rich, at 1/2 to 3/4 throttle. It should clear out under full load/throttle. Good Luck.

 

Your compression is way too low! You need to do some top end work. You really shouldn't need to rejet with a pipe because pipes actually make an engine run richer by pushing the unburned fuel back into the cylinder for it to be burned. I doubt that is the problem. You probably need a bore and piston which will run about $100. You could take it to a shop and have them check the bore with a dial guage. This should be free of charge and only take a few minutes if they are the least bit competent. Stock compression is between 160-170 lbs I have found.

 

your compression is waaaaaaaaay too low..my stock motor got to 150 lbs once, and the piston was just starting to let go..I'd take it apart pronto!

 

The compression is defentily a problem that needs to be fixed first but your reeds could also be a problem. If they are worn, split, weak as where they just flutter instead of snapping open and close. There are a lot of good aftermarket reeds out there to choose from. hope this helps

 

i have an 87 250r and it did have 260p at .060, now it is .080 with a cr 250 head gasket and now it pegs the gage at 300p. you don't need know head work just bore it and be on the road.
ct-racing and duncan racing told me it wasent possible to have that much compression but there full of **** and i can proof it.

 

Jordan250, if your talking psi, well that is basically impossible, there is no way the crank bearing seals could withstand 300psi of compression. If you get too much compression you will eventually blow out the seals and then the engine will seize in a hurry. Not only that, but if the only mod you have done is the thinner gasket, then then you may be around 180-190 psi depending on the thickness of the gasket. I know, my brother also has an 87 250R with a thinner head gasket, and yes he has enough compression to require race fuel, but its not near as high as my race engine is and its not much over 200 psi. Also, at 300 psi, you wouldn't be able to start it, mine was once on the high side (maybe 220 psi =/- a little) and not even the strongest people I know couldn't start it, so I put a less compression dome in.

SandDraggin is right, if you have broken reeds, that could be a source of compression loss, but if the top-end hasn't been messed with in awhile, I'm guessing you need top-end work done.

Good Luck,

Sickman