You might want to check for leaks. What I found on my MACH .26 engine during the first 2 tanks of breaking in was that the Hi Speed needle fitting was loose. Dont actually dont know what the actual part name on the carb is called, but its the bronze fitting where the fuel line is connected right where the throttle spring is hooked on to. I was spilling fuel all over the truck and thought I was just running rich, but was actually the Hi Spd needle casing just being loose. Try tightening that up. Might also be a good idea to pull off the engine and do an overall inspection and tightening. Check all fuel lines, screws, carb neck tightness, etc. I would go as far as tearing down the whole engine if the problem persists. A few years ago, I once had a brand new, never started Dynamite .12 TNT engine where I had this same problem as creyc. After 2 hours of trying to start the engine I finally got frustrated and decided to tear down the engine. As I took the cooling head off I noticed that the piston had a pin sized hole going straight down the piston head. The engine had enough compression to start but after a 2 seconds, then just die out. Don't want to knock on Dynamite engines, but just had weird luck with them, thats all. Hope this helps your quest on getting that engine to run like you want it to.