I have one. Mine was unreliable also. I did find a tank problem that was causing some of my problems. Additionally, I did find that running high nitro content fuels did cause some overheating, so I ran 5% fuel with 20% oil. This did seam to help. I think your problems are heat related. I might add that when, my engine was running well, it made great power. The .91's little brother the TT .53 FS is a great engine and very popular overseas. Remember, overseas nitro is very expensive, so they run FAI fuels with no nitro. You might try it.