My Tower engines smoke. Very little break in, fast and powerful. Large FP40 venturi, .283 diameter. FP needlevalve. Powermaster 5%, %22, (50/50 oil). Are you using all castor fuel, that might be your problem. I have run these engines using a stock muffler. But not for long. I use tongue mufflers that are free flowing, lots of holes. Also muffler pressure to a non-uniflow vent. Engine doesn't appear to be glow plug sensitive. Sometimes we use the hot Enya plug either a 6 or a 3 to calm down an FP. Forget which one. But I'll check. Frankly I abused the last two Tower 40 engines, setting them up, adding an extra head gasket. Very little break in, a tank on the ground at the most. Then ran them hard. Is there a lot of pinch? You may have an exceptionally tight one. Check the usual. Fuel leaks. O ring snug under the venturi. Needlevalve hole aligned with the venturi and tight. Back plate bolts tight, etc. The last Tower engine I used was literally put on a big foamy and run hard. It didn't quit. Not my most powerful Tower, but did top 12,100 turning a 10 1/2x4 1/2 apc. An extra head gasket will probably tone it down and give me a 2,2 break. I had mistakenly taken the engine apart a few times trying to locate a conrod or piston pin click. After checking everything and putting a nick in the piston, I tried another new Tower 40. THEY ALL CLICK. So. Onto the foamy sport plane to see if I damaged the innocent powerplant looking for problem that didn't exist. The engine worked.