(quoted from post at 08:48:59 11/18/17) Gentlemen, Please do not take my lack of response to specific suggestions as being dismissive or disrespectful in any way. The tractor is 300 miles away from me so I can't simply run out the door to the shop and do things. Believe, if I could have I would have. So given the reality of my situation, I looking for ideas and theories to test when I next have a chance to work on it which will likely be in 2 or 3 weeks.
With respect to the specific test of fuel flow. Last time I worked on the tractor I did remove the plug from the bottom of the carb and I am quite sure it would have past the pint in 2 minutes test. I know for certain it was a dramatic improvement from my previous test, the difference being I had replaced the inline fuel filter.
With respect to the specific test of the spark, I will certainly do that test next time. I like the simplicity of that test.
With respect to the advance weights, I have not inspected them, but I will.
I am also trying to apply some logic to the situation, given that I have already attempted to address common issues. One particular test I did stands out in my mind. I start the tractor and it seems to idle just fine. If I disconnect the spark plug wires on cylinders 2 and 3, there is no change in how it idles. If I disconnect either wires 1 or 4, the engine dies. That causes me to ask the question "what could cause a lack of combustion in cylinders 2 and 3?" Given that cylinders 1 and 4 appear to run fine, and the fuel flow test mentioned above, I don't think the issue is with fuel. Thinking I might have crossed the spark plug wires on 2 and 3, I reversed them which caused an occasional backfire through the carb. From that I conclude I had the spark plug wires on correct. When I installed new plugs, did I get a couple bad ones? I replaced both plugs and, again, no change. Next I wondered if it was sucking outside air into cylinders 2 and 3 instead of a fuel mixture. I sprayed starting fluid around the intake manifold and it made no difference. Pursuing the manifold possibility 1 step further, I removed it, cleaned it, tested it and reinstalled it with a new gasket. No change. Which leads me to say "I'm stumped". If I am asking the wrong question, please tell me.
Again, thanks for the suggestions and I will perform the 3 tests when I next get a chance. If anyone wants to suggest other things to check, I am all ears.