i had a similar problem with my original first run extechs and i had to seal up the carb neck, seal th epinch bold, and put a small zip tie on the carb boot. after i did this i replaced and check all my fuel line, fuel filters, and tank(rc8 nuff said) and it was fine. also mine was not shimmed properly for 30% in the first run of engines so i was running a p7 and once i shimmed it properly and went to a p4 it was golden. hope this helps.