Scary buzzing on Zuma

[islandscrub]

Heya guys,

So I just got my bike back from the shop. Had a 72 Contessa put in along with a new polini variator, clutch springs, gearing, and an upjet. The rest I had left stock (carb, exhaust) I just wanted to see how it would be. I ended up buying a used chrome Leo Vince ZX they happened to have in the shop for later.
    Anyway, on the way back home I noticed a wicked buzz coming from .. well, not sure exactly. If I stick my head down there it sounds like it's coming from the flywheel side. The buzz only really shows up when you left off throttle/start coasting, down rev, so my friend was saying. I tried flipping the kill switch and seeing what ti does while coasting, and the buzz seems to die off with the revs, but comes right back when I flip the switch on. I have a video of it, it happens even when the engine is cold.

BUzzBuzz

I took it back to the shop and he said it was the piston rings, but it seems so loud, and I don't recall it happening after I put the 72 on my china special.

Also, does anyone know the spark plug that should be used with the Zuma Polini Contessa?

Mahalo!

[spaz12]

What gears did they install? Link? Straight cut gears sometimes make a lot of noise.

Without running the motor try to get the back wheel to spin sorta fast, like riding down a hill... See if you hear it then.
Another thing could be the spacing in the gears. If got gears that had to be installed onto the output shaft and they weren't spaced correctly then that could also be a problem and make noise.

[islandscrub]

Not entirely sure what the gear numbers were, but this shop only uses polini stuff. He said he was aiming for 12 or 11:1. The sound isn't coming from the rear though, at least that much I know. The buzz comes out even if I blip the throttle while holding the back brake.

[edwardtennant]

crankcase vent? on my qmb scoot when the vent hose broke off it made a buzzing noise when on the throttle. Not sure it 2 smokers have crankcase vents though

[tsimi]

the shop and he said it was the piston rings

If that is true then I would quickly check the carb jetting.
Piston rings should not sound like that.

Is something touching the air shrouds?

[90GTVert]

The first thing I usually try to do with a noise that I'm unsure of is to start eliminating possibilities. You can try to look for signs of contact on the flywheel/pickup/stator. You could try to run the engine without the variator and belt installed to be sure nothing is going on there. Check the starter system out to see if anything could be making contact at times. Make sure nuts and bolts are secure, the stand isn't rattling, etc... Beyond that, it may be in the engine. Possibly poor clearances?

Dec 18, 2017 17:27:50 GMT -5 edwardtennant said:

crankcase vent? on my qmb scoot when the vent hose broke off it made a buzzing noise when on the throttle. Not sure it 2 smokers have crankcase vents though

2Ts don't have crankcase vents. Would be a really bad thing for our 2Ts, since they move mixture through the crankcase.

[islandscrub]

Thanks all for the input, I will hopefully tear into this after Christmas and post up my findings.