Strange new noise, please help

[scosgt]

So it was beautiful out today, took a 30 mile ride.

On deceleration ONLY, in just one little spot on the throttle, I get a high speed clanking noise. Can't really describe it further. Throttle up or down just a little bit, it disappears. This is only when coming down hard from WOT. In fact, I was up in a hilly area, and this was mostly going downhill, from 40 or 42 MPG, closing down the throttle, in just one spot, funny noise from someplace in the rear. As soon as I change the throttle setting, it is gone. Fresh gear oil, all exhaust bolts are tight. The bkie performed perfectly, no hesitation, plenty of power. This is a Benelli M50 two stroke with 2500 miles on it.

Anyone have any ideas where to start looking?

BTW, I added a tach today. Not sure how accurate it is. Idle seems high at 2400 RPM, WOT on a level road it gets up to just about 9000, WOT downhill at 42MPH it hit 10,400
Not sure if this is realistic or not.
Engine is the Minarelli clone, 40QMB.

Another thing, I was riding afterwards wearing a brain bucket. I heard something new in the exhaust - like when I rev up then back, there is a "back" sound in the exhaust. Like an echo. Delayed. Maybe it was always there, maybe I never hear it because I ususally wear a full helmet? Or maybe my exhaust is going bad?

[90GTVert]

If you have no other symptoms, I'm not sure that I'd worry too much over a noise like that. Mine makes noises on decceleration too. You could take off the CVT cover and be sure everything's in good condition. If there is contact of any sort where it shouldn't be you can probably see evidence of it.

The tach readings sound reasonable. You may wanna adjust your idle. It should be able to idle around 1800-1900RPM.

You always hear different sounds when you go from a helmet that covers your ears to one that doesn't.

[scosgt]

The scoot won't run at indicated 1900 RPM. In fact, the rear wheel starts to turn at 2700 indicated, I guess the tach is off by a bit.
The thing has two wire leads, but all I have to do is touch one lead to the spark plug wire and I get a reading. Grounding does nothing.

[90GTVert]

Is the lead wrapped around the spark plug wire? If it is, you could try more or less loops around the plug wire and see if anything changes.

[scosgt]

Yes it is a wrapper, and it does not change from when I just touch the wire to several loops.

[Skoot]

The noise you're hearing is the 'play' or clearances in the transmission (transmission, meaning everything between the variator and the rear wheel). you can hear the noise(s) when you are neither accelerating nor de-accelerating... in other words when the gears, etc are "floating" with NO load on them. You might have just a tad too much clearance between the moving parts or you might need to check the gear oil level. Its normally not harmful, unless you hear a loud clanking noise when you 'gun' the throttle after slowing down.

[2strokd]

It could be a little spark knock.?. I had this problem with my new 70cc setup. Vert has also had problems with detonation. I was new to spark knock with 2 strokes, but it sounds kinda like metal to metal or the piston slapping around, a really nasty noise to a gearhead. This only happens when you ride when the scooter is warmed up? Mine used to get worse the more i rode. I ended up fixing mine by putting a short shank plug in. The Polini kit i got recommends a long shank plug but it wouldnt work for me, so i put in a short plug and the spark knock is gone. Your symptoms sound about the same. Can you tell if the noise is coming from the front or the back of the motor? Its hard to tell sometimes, especially if you are riding. Hope you figure it out.