weedwacker ultralight 21cc vibration problem
 

I have converted one of these with a CH ignition and prop hub. It has a mid range, 4000 to about 5500 rpm shutter/vibration with all four 15" props I have tried. The 16" prop does the same at lower speed. It is a very significant and somewhat scarry vibration. The hub dial indicates to about 0.002" all the way out to the end of the prop shaft. I JB welded all thread to be sure it stays true. The props are new and seem to be well balanced. Is this a characteristic of thes engine I need to accept?

RE: weedwacker ultralight 21cc vibration problem
 

First,make sure the prop is balanced and not just seem to be balanced with a good balancer.
After this,rotate your engine until the prop is at TDC.
Next,alighn your prop at a 90 degree to this or so its pointing at the 3 oclock to 9 oclock position and try again.
Also,what is the timing set at?Is it Synchro spark?Should be set at 28* degrees BTDC.
Sometimes if your low needle is rich it will vibrate.

RE: weedwacker ultralight 21cc vibration problem
 

I'll try rotating the prop to TDC. The timing is set at 32-degrees per the instructions. The props are master airdscrew black glsss filled jobs. I don't have a real prop balancer. I just check one by balancing it one on a knife edge. It looked darn good. Can you sand the glass ones anyway, five props all bad???

RE: weedwacker ultralight 21cc vibration problem
 

MOST MA props are way out of balance, the few I use end up having all the paint sanded off one end.
Single cylinders all vibrate at some RPM its impossible to make a perfectly smooth single.