1. Head gaskets are last, since that is probably not one of your problems.
2. I also bet your heat riser is stuck shut. I also cut them out and seal the pivot holes by tapping and plugging with stainless bolts.
3. Try an oil change of 20-50 VR1 Valvoline racing oil with a good oil filter. Change both every 3,000 miles.
4. Did you use good intake gaskets or did you use those worthless stamped steel ones?
5. Your choke has to be shut when cold, open slightly as soon as it starts, and be full open by normal operating temperature.
6. Do you have a points ignition and where is your timing set?
