I'm working on a Stihl 028 and not having much luck with it. It starts up and runs but within a few seconds it starts running heavy and then it dies. I've cleaned the carb twice and it has a new kit in it. I set everything by the book when I put it back together and still it does the same thing. I can't get it to idle down without it dying, tried adjusting the carb to where it runs the best but it still runs too rich. I took the muffler off and checked it and the piston and both looked good, no large amounts of carbon or blockage. The saw doesn't have much power when you give it the gas, takes awhile for it to get up to speed and it's a slower speed at that. It doesn't seem like an air leak, just the opposite. Gas tank vent is good. Any ideas?