the engine is a new build, buy a pro in Denver. was full assembled when I picked it up. fires right up, without hesitation. no poping. but when you get the engine to 2500ish, it bogs really bad, and then starts poping out the carb. just went out and double checked timing, advance, cap, rotor, and adjusted points to .010. will leaning out cause the poping in the carb. YES I was sure it was rich mixture, but was just told that running lean will cause your eyes to burn as well. hmmmm now really stumped.