Several members of our club have experienced throbbing, i.e. engine speed increasing and decreasing, when flying. The usual causes such as foaming or air leakage through the fuel lines were checked out with no trouble found. The trouble was duplicated with movement of the needle valve. It seems as if air was leaking through the threads of the needle and the needle holder. The stock needle valve was replaced with one that is slightly longer from an OS-61 2 stroke carburetor that was handy. The results thus far are very good, no more throbbing.

Does this sound right to you? Comments appreciated.

Thanks,

DaveB