I have a stihl 44cc engine that sometimes wont pump. not sure why. even with my finger in the bore it still wont pump. the next day it will....??? Go figure... I tried replacing it with the carb from my Mac 46 engine that was recently removed from the saw which ran great but has not been run since removed. When i put it on the stihl it just shuts off above 1/2 throttle. The mac had an external primer bulb that has a nipple on the carb next to the needle screws. Should it be blocked off or open? Maybe i should just get a new carb? Thanks for any words of wisdom.