OS 70 problem
 

I have an OS 70 surpass that is having problems.
I am running 15% nitro 20% 80/20 oil , OS F plug ,12-8 and 13-6
props. It will idle all day with no problem but when i try to set the high speed needle it gets to about 8000rpm and still running too rich it takes about two more clicks on the needle and the rpms jump to around 12000 and the engine shakes wildly. The transition is great it just won't tune on the top end.
I thought it might be the fuel tank causing it to go lean but i replaced the tank with one i tested and the same problem occured. Props are balanced well.
Any ideas would be greatly appreciated.

Thanks, Barry

OS 70 problem
 

My OS 70 turns a 13x6 Zinger at about 9500. It seems to vibrate plenty at that rpm, I can't imagine it spinning 12000.

OS 70 problem
 

It vibrates so hard that the head is a blur!