ORIGINAL: stevenmax50
I will try that tonight Jorge, thanks. FYI, I have taken my fuel system apart and put it all back together, checking the lines for leaks, clunk position, or anything visually obvious. No luck there. The LHS recommended the fuel change to increase RPM. I was topping at 11000. OS website shows a max RPM of 16K.
That's 16k rpm on a dynomometer where the operator can reduce the load on the engine to allow it to rev up that high. That is not a practical rpm that you should be able to attain on a propeller. Your engine is running right where it should with the prop you have mentioned. The 15% nitro fuel certainly won't hurt the engine, but it is a waste of money for an OS .65LA. What 15% nitro fuel will do is broaden your needle valve settings (makes the needles easier to adjust).
I'd take the carb apart and look for particles or threads of plastic fuel tank/fuel line that have gotten loose in the system and plugged your carb's jet.
What kind of clunk do you have in the fuel tank? Is it a sintered bronze clunk? Sometimes this type of clunk can plug up after years of storage. Lots of folks used to remove the clunk and put it in the flame of a propane torch for a little while in order to clean it up/out.
Keep plugging away, you'll find the problem.
Ed Cregger