Weird knocking noise on my bike under load

[cheese]

I was at the WMCC ride the other weekend, and my bike started making weird noises under load and it was like a weird knocking noise. The power didn't feel too out of the ordinary, so I thought it was probably a snapped power valve cable, but both look fine, I've just checked it but not pulled it out (I'll do that next).

Its just had a new piston fitted and it's done about 4 hours on it so far. Its been running really well.

what else should I check? The brake pads are all well worn and due to be replaced, but I doubt that would make the noise??? Also the noise didn't seem to be at the same speed as the Revs (thats why I thought it was the power cable). Oh the bike is a 04 CR250.

[Rupe]

I was at the WMCC ride the other weekend, and my bike started making weird noises under load and it was like a weird knocking noise. The power didn't feel too out of the ordinary, so I thought it was probably a snapped power valve cable, but both look fine, I've just checked it but not pulled it out (I'll do that next).

Its just had a new piston fitted and it's done about 4 hours on it so far. Its been running really well.

what else should I check? The brake pads are all well worn and due to be replaced, but I doubt that would make the noise??? Also the noise didn't seem to be at the same speed as the Revs (thats why I thought it was the power cable). Oh the bike is a 04 CR250.

burn it, then get something more practicle

[LittleJohn]

Does it make the noise when you sit there and rev it our of gear or only when you are moving??

[vr4king]

Power band getting loose maybe?

[barty5]

Power band getting loose maybe?

You mean rubber band ????

[sugilite]

Crap/contaminated fuel causing detonation?

[B0000M]

id first blame non 98 or higher fuel, - detonation

another thing to check would be the upper chain roller (on the sub frame) it makes some nasty noises when the bearings are flogged out, but only when the rear suspension compresses.

[barty5]

id first blame non 98 or higher fuel, - detonation

another thing to check would be the upper chain roller (on the sub frame) it makes some nasty noises when the bearings are flogged out, but only when the rear suspension compresses.

Oh shit are we back on stale fuel again:facepalm::laugh::laugh:

[CHOPPA]

chain.............

[cheese]

Ok, given its a new piston and the compression is up it probably is detonation. I'll treat it to some 98 or higher.

[Ktmboy]

chain.............

Chain....?? Start with the basics.

[B0000M]

being a cr250, with possible low grade fuel, and a new top end (more compression), and under load, and cr250s being notorious for detonation on poor fuel, and only under hard load, and only after cheese filled up half way thru the day, all things point towards detonation

[barty5]

stale fuel again:facepalm:

[B0000M]

lol, cheese- the ONLY person i know who ever has stale fuel issues