We ran a Contenental 0-200 on Mogas for years without any issues, then we developed a loss of power during climb out. The carburrettor had been replaced prior to the loss of power and eveything else checked out. I went flying with the pilot to see for myself. I wish I hadn't, it was very uncomfortable feeling as the engine sagged at 3-400 feet. I was very pleased when we got back on the ground. As we were short on ideas it was suggested that we dumped the fuel
(the aircraft was flown regularly so the fuel wasn't old). The problem which had occurred on each of the previous flights went away and has not returned.
We run solely on Avgas now. Relatively fuel is cheap and accidents are expensive.