Need help

I have a Miller Big 20. It is pretty old and I am having some issues with it. My question is were on this computer can I go for troubleshooting tips? It has a teledyne Continental motor, 4 cyl gas. A Marvel Schebler carb. I rebuilt the carb. It welds fine when it will start, it starts fine when the motor is cool. As soon as you use it for a while and shut it down come back after lunch, it will not start. Could ya'll please tell me a website to go to or maybe one of you have had the same problem. I have taken 2 yrs. of college mechanics and this thing has me puzzled. I would greatly appreciate any input.
Clay clayalwin@yahoo.com thanks

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