David, I feel for you and if you get the problem solved, let me know. I have been fighting the same issue on my 1650 for the past few years. I have had the tank off 3 times. The last time I pulled the shut-off assembly out and made sure the screen was clean, and it was. I also have tried 2 different coils, new points and condensors, spark plugs and wires. I even pulled the head to make sure the gasket was not leaking. The last time I pulled the engine to make sure the fins were not filled fill of crap causing the engine to overheat and they were as clean as can be. I finally put a mower deck on it and just run it. It now runs for about 1.25 hours before it will act up. It will not quit but acts like it is out of fuel, then catch itself and away we go for a couple minutes and then the same thing again. Like you, it has lots of power and runs like there is not even a 50" deck under it no matter how thick the grass or how tall it is. Unfortunately, I have not had to mow grass for for over 6 weeks. It may not get used again until the snow flies.