I've been having this problem with my engine. It'll sputter after I let out the clutch and kept dying and never started. I messed with the carb and replaced magneto, nothing. Then I replaced the cdi yesterday and it started right up. And even know the cdi is electrical, I still had spark with the bad cdi
Literally, hold the plug, lightly spin the back tire. Get a tingle? It won't really hurt unless you give it a good spin, but you still need to rotate it enough, or just push the bike in pitch black with the plug on the head. lol. I always upgrade my coil and cdi. Never have problems with them, I even weld with them still attached to the bike and hooked up. I keep forgetting to unhook it.
When you pull fuel hose at carb, fuel just runs out of line till you shut tank off. Thought it might be that. Maybe its these new knock off tillotson carbs are both bad, but I wouldn't think 2. It acts like something to do with pulse port. But I've taking carbs apart & everything is in order.