Thorp Air Command - T18.net

Hey Everyone,

Had an interesting engine issue develop recently in 78WG. When attempting a touch and go, immediately after pouring on the coals, the engine would momentarily drop 2-300 rpm then spin back up. There was noticeable roughness in the pattern with the mixture full rich and the problem repeated itself when run up on the ground. I had the carb pulled and overhauled it, but everything checked out.

I took it for another spin today, and prior to flight could not repeat the issue. Flew it for 30 minutes and returned to the pattern, only to have the same issue. I did a mag check post flight on the ground and it checked out at 1800, but at max, mixture full rich it would drop from 2100 to 1900,then slowly continue to fall. If I leaned it out and the mags both check out with about a 75-125 rpm drop. Definitely seems to be running too rich across the board, but only when it’s warmed up. I’m stumped. Here’s some other data:

DA: less than 2500’
Engine: Lycoming O-320
Mag timing check out good
Some surging full rich, idle power on final
Only happens when warmed up

Any thoughts? Trying to get this sorted for Oshkosh....

-Andy