Was having problems with the Edelbrock 600cfm carb (I thought) on my 400 Pontiac - just could not lean it down. Wouldn't idle smoothly. Wasn't terrible - no black smoke, etc., plugs burning OK but, was very touchy on hot start. Never failed to start but, don't even think about touching the accelerator pedal - it would flood. An additional frustrating symptom was that it would just quit at about 70mph when under full throttle from a dead stop, but would run normally immediately after letting up on the pedal. Yet...it would not do that every time (aaaargh!) I changed jets, metering rods, springs, accelerator pumps, numerous times; checked for vacuum leaks, played with timing, went through the distributor, etc., etc. Still had the problem. Then, I read that this carb does not like fuel pressure above 5psi. Put a fuel pressure gauge on the line...the needle at idle was a blur between 3 - 7 PSI, and between 5 -9 psi as throttle was advanced. So...a new mechanical OEM fuel pump settled it down to a slow needle pulse between 4 1/2 - 5 1/2 psi; a Holley pressure regulator adjusted it to a steady 5 psi. Gas mileage jumped up 2 mpg. Noticeable increase in power and torque. Idles smooth. Ol' "hoghead" learned a lesson. Hope this info is useful to others on the forum.
i have been fighting something similar on an 84 305 upon hot restart after sitting about 5 min. took off the lid of the carb and was watching the fuel boil in the bowls. i hear that is common on aluminum intake motors.
84...don't know how common it is but, have witnessed several of my buddies alleviate that problem with carb spacers of various thickness. The spacer provides a better thermal break between carb and intake. Thickness of an inch, or more, will also provide a small, but noticeable, increase in power and slightly better gas mileage.
