250r missing in topend

[jkwearls]

I have an 87 250r, and for the last 8 months it has been cutting ou in the top end like it is running to rich. When it is sitting and you rev it up it backfires and cuts out. Ihave had the electrical system checked by a dealer put a new stator and switched cdi boxes and coils with ones that are known to work. i rebuilt the topend and have changed the jetting to way to rich to way to lean and it doesn't seem to help i even put a different carb on it. when i check the jetting the plug is the correct tan color and it doesn't have excessive smoke. the motor is a stock bore with a mild port job. it also has v force reeds and an fmf fatty pipe. it runs fine through the low end and mid range. Any help would be very much appreciated i am running out of ideas

[ghak99]

Might be a dumb question, but nowhere have i seen you bought a new plug? Some times they are picky about their plug gap too.

What compression are you running?

[jkwearls]

i did change the plug several times and always checked the gap. The compression is above stock but not so much you can't run pump gas i can't remember the exact ratio

[ghak99]

You getting the fuel mixed right?

Too many people overlook the simple stuff like this is the only reason I am asking these basic questions?

[Got nads?]

Have you had your engine checked for possible air leaks?

[jkwearls]

thank you for the help. I have been running the same fuel mixture as when i got the bike 32:1. Ihave had the bike for about three years and it ran fine up till about 6-8 months ago.

Ihaven't checked for air leaks, i'm assuming you mean to check the crank case for leaks. It has no oil leaking from the stator cover side, and it has never used a drop of transmission oil. I was under the impresion if the crank seals were leaking it would start using oil, but i am far from being an expert any help or ideas anyone can give will be greatly appreciated.

i also int the original thread forgot to mention it has a clean k&n filter, and a stock carb with a 155 main and a 48 pilot jet

[rodenberg35]

Have you checked the reeds. You could have a prob there

[jkwearls]

yes i have checked the reeds even took out the aftermarket and put the stock ones in to see if it made a difference. it didn't.

thank you for the idea

[pairanutz]

i had this problem on my R -no matter what size jet i ran it would miss on top -it ending up being the magnetto and the pick up coil-it tested fine but when you reved it up it wasnt putting out enough juice -hope this helps

[rodenberg35]

I had the same prob with the pick up on my x. It tested fine but I had to replace it to find it was bad

[jkwearls]

i just put a new stator in about two weeks ago.

thanks for the ideas

[ghak99]

I am not great w/ 2 strokes, but if you are not sure of the compression try running a little hotter gas just to be sure the problem don't go away.

I would give your electrical system another real close inspection. I personally don't trust any dealer, most of their "mechanics" couldn't poor piss out of a boot!

Look for any signs of broken wires and be sure any grounds are getting good connection.

Did this problem come up out of the blue while riding or right after you had just worked on it?

[jkwearls]

I completely tore the wiring harness apart looking for broken wires, everything apeared to be ok. took the ground wire off and made sure it had a good clean connection. Even before i yook it to the dealer i traded coils and cdi's with my buddys bike that runs fine, with the exact same motor work done. The only difference between the two is that he runs a lectron carb.


I have been running 110 octane fuel in the bike, and the freind with the same motor runs 92 pump gas with no trouble. I also was having this trouble before i rebuilt the motor.

When i did rebuld the top end the rings were stuck to the piston causeing low compression i figured that was the problem. Is it possible the engine didn't break in properly and still has too low of compression. when i recently checked it it had about 165 is that enough?

thank you for all the help.

[jkwearls]

Thank you everyone for the help i found what the problem was. The motor was not getting a good ground to the frame. Its always the simple stuff.

[ghak99]

good to hear! Crap like that will drive a man crazy.

[Narly R]

Glad to hear ya figured out the problem! And welcome to the site, and by any chance do you race at salem? j/w

[jkwearls]

No i don't race mainly just ride the dunes

[sandspanker]

:confused: had the same problem with my R. changed everything one at a time off another bike. the last thing i changed beleave it or not was the flywheel the magnets were going bad in it .ran like new after that. something too keep in mind.:D :D