[AJD] Model 40 Question

[wb5cys]

My model 40 cranks on first turn even in freezing weather. Compression is 
perfect, oil pressure is perfect. When I first start it, the tractor will 
run for about 30 minutes great, then it dies as if it ran out of gas. I 
restart it and it restarts fine and runs for about 5 minutes then does the 
same thing.
If I let the tractor sit for about an hour, it will run for another 30 
minutes before repeating the cycle above.

Any ideas on what might be my problem?

Thanks!

Cal Barton
Nacogdoches, Texas