weird grind

hello, just bought a 89(i think) ds50. flatreed engine. easy starting, great idling, fast running, like 35 probably. its stock with 12/12 carb. anyways, so the problem is when i start to get about 2/3 into the throttle i start to get a crazy grinding noise that kinda comes in and out. i tried revving on the stand and i can sit there and rev all day but theres no grind. so it only happens like like 25-30mph. i checked the front wheel and it seems fine. feels like its coming more from the right of the engine. the covers are off and when i look under there while i rev i see nothing noticably wrong, but again it doesnt happen when on the stand. gotta be the variator right? ive never had bikes with a variator before. if it is the variator wouldnt it do it on the stand too?

Re: weird grind

Downhill Harvey (OFMC) /

Take the belt off, grab the variator, and see if it moves up and down, or forward and backward. This is to check the crank bearing.

Re: weird grind

nope, snug. i saw a post somewhere where they had loose carbon in the exhaust, maybe thats it. im ordering a pipe anyways, so we'll see.

it seems like its possible its the variator weights or something, cause when you spin the clutch around with the belt off you can hear them moving, but thats a steady sound, this isnt a steady sound.

i dont understand why it would only happen with weight on the bike though.

Re: weird grind

If was a bearing or ring or something, wouldnt it grind even when on the stand?

Drive train side seal is super leaky but everything is still running good...

Maybe that has caused something to fail and I just don't know what yet.

Anybody else had this problem on a derbi?

Oh yeah the engine is giving off a whistling sound now intermittently.

Maybe it's just a noisy ride...

Re: weird grind

Downhill Harvey (OFMC) /

If it's dirty behind the drive side (or any where), the seal is bad. It will also be sucking in air. Remove the clutch, clean behind there real good, and replace seal. You can replace the seal without splitting the case, or even removing the engine.

Re: weird grind

Ah, really? That's great cause I have no space to do work. So much smoke. Might as well order that 12 tooth while we're at it

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