Working on an Echo 440 EVL which I can't get to run except on a prime then it dies quickly. Carb has been rebuilt but upon my inspection I noticed no pulse coming from the impulse line. I pulled on it and it seemed to be hooked up but I couldn't see the end of it nearest the engine. I blew through the line and it wasn't stopped up. Not sure what to do next, hate to tear the whole saw down just to find the line probably hooked up anyway. Saw seems to have good compression but I checked the impulse again and it's just not there. Any ideas?