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Try to determine which cyl(s)are skipping. You could have a couple of valves that are adjusted too tightly. As the engine gets hotter, the valve gap will close causing the valve not to close completly. The 'poofing' when cold would indicate that too, as it is right on the edge of not closing even when cold. OR it could be a head gasket blown between two cylinders. Do a compression check both hot and cold to see if all are about the same. OR it could be you have a broken valve spring which prevents a valve from closing. I had this happen -twice - and I know of others who have too. It's common. A compression test will help you narrow it down. If you find a compression problem, remove the gas tank, take off the valve cover and check the springs. Check the valve clearance at the same time if you don't see a broken spring. From what I hear from you, one thing or another is going to make you pull the top off. UNLESS you have the spark plug wires on the wrong plug. This will make it seem as if it's running ok slow, and cold but when revved a little it will miss real bad. (I think this is less likely, but check first) This is my humble guess based on the facts you presented. You've eliminated bad coil and point, etc. Maybe someone else will have another idea for you. I wish you luck and your tractor a speedy recovery.
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