I spent two hours changing the fuel lines around on my grass trimmer recently because I was not sure I had hooked them up properly after having replaced them. The engine would start after priming and a few good pulls however it would die after only a few seconds.

Eventually the Internet told me that my carburetor was probably dirty. I took the carburetor apart, and wiped everything off and rinsed it with fuel. It did not seem to be dirty at all but sure enough after resembling everything the engine ran great for at least ten minutes (during which I set the low and high idle screws as well as another idle screw which basically holds the throttle open). I set it aside and came back the next day only to find the same symptoms I had had the day before -- run for three seconds and die. I talked to the Internet again as well as a couple of people in real life who mentioned that my fuel mixture may also have gone bad. Well I did not have any gasoline left but I did have some kerosene so I dumped a fair bit of that into the tank and viola, all was well again.

So if you have a two stroke internal combustion engine which has had fuel sitting in it for several months causing it not to run properly or at all:

• replace fuel in tank with clean fuel mixture
• take apart and clean carburetor with carburetor cleaner and compressed air
• clean or replace the air filter
• replace fuel filter if one exists