Hi there,still fighting with an engine noise, which i think i located now. At a certain rpm, the motor rev, it s a mixture of whistling and vibrating, what i really would like to get rid of. Found out now, that i can hear it also with engine off, turning the crank.
Never heared that anywhere.
My OEM  reeds, i inspected, are not flat, they are very slightly bend. 
It´spossible to mount them both ways. If the bend is towards the block, the reeds are fully closed. The other way around, there is a 2mm gap on all 6. 
Putting in carbon reeds, which are totally flat, there is about 0.5-1mm gap.
Both, in case 1 and case 3, the noise is there.
I am out of ideas. Motor otherwise runs fine. Cylinder holes and channels are not tuned. Piston and bore new.
Also new crank seals and new intake.. Pressure test shows no leak.
What could it be ?


 

This noise is a characteristic of reed valve engines when turning them over slowly.  At running speed or even kick starting speed you shouldn't hear anything.

My DT400 does it, a sort of wheezing souund if you kick it over slowly, or turn teh flywheel by hand.

Once fired up no noise.

If you ever looked at the inside of a duck call it is very similar except only has one reed. It sounds similar too. If the Yamaha reeds were softer it would probably sound like a fire breathing angry duck.

The old 'reed valve squawk' trick. I remember when wee first got the reed models in "72 & had us all crowding around haha. Doubt it'd be audible running though. Bigger motor bigger squawk. There's a danger in turning them over 'i think' as get used to fluttering one way. Have broken one or seen them broken but that was in motocross revving hard all day. Back in "78 yamaha sent us thinner reeds to try in my yz125e but ran no different--better or worse.

Buggin you nailed it!!!

Hi all, thank you for reply.
As you stated,noise with motor off, the noise turning the crank is normal, ok.
But this noise appears always, when i pass about 2000. Means every shifting or slowing down is guided by this noise for a few secounds.
Didn´t have that the past years, now it´s there.
Must be a reason, why...
 

Would be great if you had a recording of the sound it makes at 2,000 rpm. 

Thank you, Mark.
Here a video of the running engine. I checked again, it appears at 2700/min, not 2000/min.

Blimey, head scratching time. I can say its not reed noise though. But what is it. Is it something like an exhaust spring vibrating, if its held in by springs at the front. Something inside the exhaust--hell i don't know. Back to school for me. Thanks for the video.