I have a 3 year old, br 600 mag. back pack blower. I have a hard time keeping it running after it worms up. It starts fine. Will not idel have to keep my finger on trigger to keep it running. I did all PM's on it. new plugs, filter, primer bulb. I cleaned out the carb. it looked good. what gives? do I need to buy a new carb? I looked at the cable, I cant tell if it needs to be tightened . I have a 550 and All I did to that one was new plugs. I have a new 600 in a box but I dont want to pull it out until I have to.