Both my "problem start" engines have that funky zero-adjustable carb that's half inside the fuel tank. I got a chance to spark-check one and the coil is weak, so I'm gonna look for another coil. These both started great the first two years, now the tank has to be refilled during a mow where it used to cut the yard 3 x's on one tank when new. New plug, cleaned air cleaner, no air cleaner - doesn't matter, it still takes forever to start. Also, they run smooth with no load, but once they hit a load they start "hunting" and on the down-rev side, they blow a black puff out the exhaust. I bought a new mower, but plan on turning this old one into a vacuum so I don't have to spend so much time cleaning up the clippings...