9n warm doesn't start

My 9n cannot start when it is warm. When it is cold, it cranks and starts faster than you can blink your eye; but after running for an hour or so, it just cranks when trying to start it.
Following the advice posted here, I have replaced the front mount ignition coil. Didn't help.
The sparks and wires were all replaced last year, or the year before that. (I just bought it last year, this is my first tractor ever :o)

I checked for vapor in the fuel bowl, and couldn't see any 'snow'. Once warm, I have checked the spark on the plug, and there isn't any. I still had my other coil (old one that I kept), and stuck that on (which would have been cold), same thing. No spark, no start.

Any other suggestions, thoughts that I can try??

Thanks for any help in advance.

Anyone's thoughts about that??

I was looking at the spark wires, and it is obvious that they were replaced recently, but the distributer cap looks to be older.

Usually its your frontmount ignition coil that craps out after about 1 hr of runnin. Swappin' a "cold" ignition coil generally and not startin' would tend to rule that out.

Generally the ignition switch internal contacts get gunked up and crap out after about 15 mins of runnin' time. But it is SO SIMPLE to by-pass your ignition switch with a jumper wire, and SO CHEAP.

The other heat/time related ignition problem is the condensor. That my last choice..... ..Dell