Our 62 t-bird starts surging when it runs for a while. Also, sometimes it starts cutting out when we are in a higher elevation. (2500ft). We have a Holly carburetor, that has been rebuilt.
That sounds like what we use to call a "lean surge" of course you will have to check fuel pressure and supply first, then the float level, if those both check good then you will have to re-jet the carb. I had a Ford truck come into my shop that the guy was said it was surging, so I drove it before doing any work on it, and his would start off by pinging slightly then stop when the surge started, I found that the spring in the vacuum advance unit got so weak that it was allowing the advance to bounce around, replaced the and adjusted the advance unit and no more problem, so listen closely if your engine starts to ping just slightly that could be your problem too.
Check fiel filter & gas lines,may be vapor lock.
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