Partial Power Loss
912ULS 200 Hours since new: Run up and take off normal. Halfway down the down wind leg, power dialed back suddenly, maybe to half. Didn't feel like a throttle reduction normally does, drop was too quick, like flicking a switch. Tried cycling both mags, no change. Still running smooth, no shaking but would not take full throttle, but I didn't try too hard, just wanted to keep the engine running. Landed non event. On ground, seemed to run ok, would make full rpm, but shook and stumbled when I went from full power to idle on the ground. Question: Does this sound like carb ice, or maybe water in the fuel? Day was abut 45 deg but mostly dry, no visible moisture. Tanks were sumped. Running 100LL but there may have been some auto fuel with methanol in the mix ( switch over for winter flying). High Wing ( RANS S7S) with aux fuel pump, but didn't try turning on pump, was too busy. Engine is kept pre heated constantly at about 80 Deg...
