Firstly these type of carbs do not have a main jet. They have two mixture adjustment screws one for low speed running (L) and one for high speed running (H) on your machine they will have restrictor caps fitted so there will be limited mixture adjustment to conform to current emission regulations. They can be removed by a special tool if you have one, but in all honesty the symptom you have with the primer have nothing to do with mixture adjustment. Likewise it also has nothing to do with your fuel mixture ratio- however, as a side note- you should always dilute your two stroke oil at the ratio recommended by the manufacturer of the oil. Most good quality oils from Stihl, Husqvarna etc are of a semi-synthetic of even fully synthetic nature and will have a dilution ratio of 50:1 which will be prominently displayed on the bottle. Never change this recommended ratio irrelevant of what the handbook states or what cc engine you may have.
If your primer bulb is slow to return, then as previously stated it could be the breather in the tank cap is blocked, the inlet and outlet of the primer itself are blocked, the fuel filter is blocked, one or more of the fuel lines is blocked or kinked, or if it has one- the fuel tank breather is blocked. Is the air filter clean? Remove the primer and see if it return quickly when off the machine- if so use a process of elimination. It certainly sound like a blockage given the fact when you want more fuel to throttle up it cuts out- that combined with a slow fuel primer action would suggest a blockage, but it could also indicate two seperate problems.
pleasant, December 2011
