first off it needs to be jetted but im pretty sure this isnt the problem. It runs perfect until it hits around mid-high power band even then it runs fine but it makes like a rattling sound like somethings loose in the motor but i just rebuilt the whole thing not too long ago. The first time i heard this i checked the water pump because it was leaking from there and sure enough the impeller was loose i tighted it and it stopped now its doing it again but louder and its not the water pump, what are some things that would cause a rattle?

 

A loose motor mount?? Check for loose bolts ie. radiator, motor mount, pipe, etc....

 

well actually the top motor mount is loose (it doesnt have the bolt) but its fallen off b4 and it never made this noise...

 

Sometimes detonation is described as a rattling sound coming from the engine.

 

That's almost what I was thinking dzzy.
What kind of rattling??? does it sound like rocks in the pipe? or a little man with a hammer????
Sounds silly, but detonation makes those sounds... and usually not for long!!!

You say it needs jetted??? If it's lean, it WILL detonate! You're flirting with disaster!

Was your motor set-up for high octane fuel? I see it's got a milled head, so that would be my first clue. Get some C-12 and see if it goes away... (After you get it jetted correctly!)
If it is detonation, your piston won't last long! If it's lean, your piston won't last long...


Good luck!

 

its running too rich right now, im gonna see if i can get it jetted today. also it will only run with a b8egv spark plug it doesnt like the b8es anymore y is that? also with the noise it does it then it stops at really high rpms and itll make it again once again when i slow down. it sounds like a little rock inside an empty cylinder. i ran high octane in it as soon as i got it back together and it ran perfect then the next day it would run like **** (if i was even able to get it started) so now im just using 91octane. thnx so far guys~

 

Sounds like an ignition upgrade is in your future! how is your plug gapped?
The 250R ignition is less than optimal when new... on an aging machine where corrosion happens in the connections, etc.... all bets are off.

Talk to ESR... they'll fix ya up!

 

If it makes the noise as you decel it makes it less likely of being any form of abnormal combustion. Detonation would more likely occur under a load. Actually, on the two strokes I'm used to working on, that would be rotax sled engines, It would probably have ejected by the time you hear any noise. It can happen so fast. Still your description of the noise sounds like it could be detonation, but then it could be something loose somewhere too. will it make the noise just sitting there, or do you have to be riding it? I wonder if 91 octane is enough to keep your ride alive, without jetting it so rich it runs like crap.

 

did you use a torque wrench?????
bolts shouldn't be falling out and loosening up.
and you know a bolt is missing in the upper motor mount but you dont replace it? its there for a reason you know. your going to end up with cracks in the frame and stress fractures. every bolt on a bike is there for a reason make sure they go back on and stay there.

 

well i was gonna jet it but it seems to be running perfect now (jetting wise) still making noise, i put a bolt on the motor mount, spark plug is gapped at whatever it is from the box, it started making the noise today in nuetral, noise doesnt affect performance (just my mental performance!!!) i keep thinking its about to blow up or something[img]i/expressions/face-icon-small-frown.gif[/img], it does make the noise loudest under heavy acceleration. Im gonna tear it open tomorrow and see whats makin that noise it driving me crazy!!!!!!!!!!!!! thnx guys~