Originally Posted by
Cougar429
What MVVS muffler and does it have a pressure fitting? How old are the fuel system components
What engine was on there before? Asking as carb height or distance to throttle centerline from the tank may have increased.
Only time I encountered something similar I had pulled the 50BB powered Seamaster from 20 year storage. Figured I should change the fuel lines so went with a very flexible clunk line in the tank. Engine fired up and would fly at 1/2 throttle or below all day. Anything above that and it would starve. After tinkering forever and even installing an OS55AX the problem persisted. Found at higher throttle settings the clunk line would actually collapse under muffler pressure.
The original engine was an OS 55AX until it died. So, I temporarily installed an OS 70 Surpass II, then a Thunder Tiger 75FS, and finally the Fox 74. The engines were mounted sideways, so the carb height to tank is the same. The distance from the carb is greater with the Fox, even though the tubing length stayed the same.