[BOB VIDAN]

73 400 with 65 intake and stock AFB 4 barrel. When it starts will run fine. As it warms up, starts to load up/miss a bit. If idle is not 1500 or so, will die. Timing and dwell are dead on. New coil with good spark. Heat tube to choke coil gets very hot, not sure if it should be that hot. Tried 2 different carbs with the same results.

Stumped. Could I have a vacuum leak? Don't hear a hiss but..........

What am I missing?

[69birdboy]

Sure sounds like a huge vacuum leak. Spray around the intake and see if the idle changes at any point.

[Tim john]

I like to use a propane cylinder with a small rubber hose attached, place hose in glass of water, get it to bubble lightly (emititng a small amount of propane) and now go around the intake gasket real slow and if the RPM's pick up you found your leak or one of them, do the valley pan and carburetor base as well. Do everything that requires a sealed surface under vacuum that can reach the combustion chamber.

Tim john---

[BOB VIDAN]

Looks like the problem turns out to be the choke preheat tube inside the intake. Was all rotted away on the choke side and was letting hot exhaust gases into the carb leaning it out so much it wouldn't run. Never seen those tubes rusted away before.