Re: "If it has compression, fuel, a good plug and the carb works right.... it HAS to run, physics dictates it. " < the engine can have good compression and still have poor engine seals. This usually makes the engine run erractic and unpredictable. IT also causes the engine to keep running even after the carb barrel is completly closed. As far as having the carb work right, based on my experience with different engines imcluding the ones I own and the ones I help new flyers with about 1/2 the brands have good carbs that work well. The other 1/2 have carbs that are finicky to get adjusted properly. The seals on some of the carbs are poor and the threads on the needle valves are course which makes them hard to fine tune. My 2 cents. [8D]