Lurker Carl wrote:My guess about sticking valves. On shutdown, unburned fuel is left on hot exhaust valve stems so varnish/gum/carbon builds up down into the valve guide until the goop is plentiful enough to hold the valve open. My experience with other flatheads with repeatedly sticking exhaust valves required removing the offenders and cleaning both the valve stem and guide. Try shutting off the fuel and let the engine die of starvation.
I'd agree with you Carl, but I always shut down, (for periods of time more than say, an hour or so), by turning off the fuel. Its on a mag, so I don't worry about leaving the ignition on. The fuel in the tank is never more than a month old, as I drain the tank anytime its going to sit for very long. It usually only has a couple of gallons in it anyway, as I only put fuel in it when I'm going to use it. The gas you buy today is absolute junk so I never let it sit in any of my tractors that aren't frequently used, and certainly not in the carbs.
I've got my "siphon hose" readily available to drain tanks. I often find my self "robbing peter to pay paul" when it comes to gas around here. Most of the gas will end up in my old H or my JD 70 which do most of the chore work around here. And that 70, unlike its diesel brother, is not very frugal on fuel. Its just an overgrown G which had an incredible appetite for fuel. I used to joke than on a 1/2 mile row, you needed fuel cans at each end. Actually, joke wasn't the right word... "sarcastically lament" would probably be more appropriate!