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On my 00 CR250R, I have a mid-throttle, low load detonation/spark knock. I retarded the timing all the way, and it helped a lot, but if I am cruising on flat ground in, say, second right before the motor rips into the powerband, it will have a spark knock sound. If I dick with the throttle, I can get a one-time loud knock. But it is usually a repetitive, steady knock. It doesnt knock under heavy load anymore (after retarding the timing), at least as far as I can hear. and it doesnt do it under a no-load free-rev.

Even before the retarding of the spark, it wasnt a consistent problem, and it still isnt, but the mid throttle thing is frequent enough to worry about engine damage on the trails, as that is right where I run my motor most of the time to avoid running out of gas on long trail rides.

You could try mixing some race gas in and see if it goes away completely. That'll tell you at least if its just an octane requirement thing..


I've had some noises in similar situations with different bikes and found it to have been simply the chain slapping a bit.

Gmbond wrote:You could try mixing some race gas in and see if it goes away completely. That'll tell you at least if its just an octane requirement thing..


I've had some noises in similar situations with different bikes and found it to have been simply the chain slapping a bit.

its definitely coming out of the motor, when i rebuilt it, the head and piston had "termite syndrome".

I will try the race gas thing. 75/25 ought to do it i would think?

I had an intermittant knock on my dune bike and it turned out to be a semi blocked gas tank vent tube, the only way I found the problem was it blocked completely at pismo and left me stranded.....

britincali wrote:I had an intermittant knock on my dune bike and it turned out to be a semi blocked gas tank vent tube, the only way I found the problem was it blocked completely at pismo and left me stranded.....

must be I'm a dweeb, I don't see how that is funny.......

You would see the humor if you saw Brit pushing his bike back to camp only to find that the tank was not venting.

Then again, I'm easily amused

Kuma wrote:You would see the humor if you saw Brit pushing his bike back to camp only to find that the tank was not venting.

Twice

Kuma wrote:You would see the humor if you saw Brit pushing his bike back to camp only to find that the tank was not venting.

Then again, I'm easily amused

Its funny that Brit didnt have something fall off to end his day... or BLOW OFF like his FMF " pipe bomb" did.

Brits always full of surprizes.....


Brit pushing his bike looks allot like this....

them 250s make all kind of wierd noises. '04 sounds just like a rod knock but it aint. dont know what it was