haven't had to post for awhile but can't work this out
after about 30 mins or so the engine starts to splutter and back fire and seems to only run on two cylinders at startup it runs beautifully I have had the rocker gaps checked and set and added all new modern parts etch electric fuel pump, electronic ignition and new coil but still have this problem
someone said it night be the rear two cylinders getting overheated but I can't work how or why they are open to the air any input is great thanks

Vapor lock in the gas line?

gas cap vented ?

Valves really set correctly?

Saw some pics on The Samba. He is running no tins on the cylinders. No need to keep guessing.

Pics are worth a thousand words

Yep just saw the pics.
Gotta have the tins on there particularly if you plan to run in the florida summer heat.
Hope it works out for you.

Be Big,
AMAC