Sounds like an air leak, but it doesnt really make sence though. But using a fuel that has a high oil conent in the fuel will not cause this type of problem. It causes OWB (One Way Bearing) problems, it causes the OWB to slip and continuely slip. The only way to get rid of this is to get a new OWB and to use a fuel that doesnt have as high of a oil content in them. Also high oil content fuel's can cause people to over compensate with needle setting. Another words to get more performance, they will tend to lean it out and will actually lean it out to much to get the performance they want and or like. So it can actually cause an over compensation of the needles to get the desired performance, but does not cause a heating problem with the engine though when richening it up.

But about the only thing I can think of is an air leak, but it doesnt make sence. Another thing that it may be is maybe the needles are bent, causing the temps to raise when richening it up cause a bent needle will sometimes cause an actuall lean condition at points and will have very eratic tunning. But those are the only two things that I can think of at this point right now.