[Tom Wells]

David,

I had a similar problem with a 557.

It was caused by fuel boiling in the float bowls of the Holley carb.

The boiling point of today's substance we laughingly call gasoline is so low that my bowl vents looked like Old Faithful. I proved this by removing the hood scoop and the air filter and watching it do exactly that at low speeds. The fuel would geyser up, make a u-turn and go straight into the intake. Instant shutoff.

Highway cruising was fine but in low speed traffic it shut down as if the key was turned off. No coughing, no sputtering, just running fine one second and dead silent the next...

I spent nearly two years trying to fix that (and spare you the details LOL) before switching to Holley EFI - problem solved!

Picture the pressure in the float bowls at zero psig and the EFI at 43 psig. That big pressure difference prevents today's fuel from vaporizing at typical underhood temperatures.

The temperature required for evaporation of today's fuel is probably 50 or so degrees lower (I knew the number but time has swallowed it) than it was 40 years ago when carbs were king.

Another thing to think about, yes?

Tom