Check fuel pump pressure.

Doubt vapor lock, but if fuel line is in contact with any hot engine components, all bets are off.

Fuel filter ok?

Is engine running on fast idle cam when first start because of a closed choke, choke opens engine off fast idle cam on regular idle screw setting which may be to slow?

Bad coil failing as it warms up?

Cracked or otherwise damaged distributor cap or rotor.

What does a vacuum gauge read at idle.

Do you have another carb to throw on it for testing?


Engines normally will run perfectly even without a battery if charging system is in order, doubt if it is failing battery.

Engine ground sound?

Run a jumper wire from battery positive to coil positive to rule out any ignition wiring issues.

Does engine have a ballast resistor in good condition.

Coil wire to dizzy sound?

Coil wires nice and snug?