i've got an edelbrock 400 bolted onto an edelbrock 1400 in my '78 bronco w/a 6.6L engine. the problem started as soon as the weather got warmer last month (so the old people say), after i went through my first tank of premium gas w/OUT a lead additive, and after installing a new set of rebuilt heads w/new hardened valve seats. as soon as i filled the tank with gas and an STP lead additive, at idle in drive, the engine would stutter. rpm got real low like it wasn't getting enough fuel. stalled a couple times. won't stall as long as i keep my right foot on the gas, and left foot on the brake. driving, it does fine, unless i'm going under 25 mph.
one afternoon of frustration, i floored it, the stutter went away. that evening i drove it 25 miles, no problems. then it started again the next day. had a guy from work that knew about carbs re-adjust it, fixed the stutter again. that was a month ago, no problems since then. same tank of gas. this morning, tried to drive it to work, started stuttering again.
i was told:
1) maybe the lead additive burned the fuel pump diaphram
2) the fuel filter was dirty (replaced, nothing changed)
3) unscrew the two idle adjustment screws in the front, spray carb cleaner in there and blow it out with compressed air, and pull a couple star bolts on the top and spray carb cleaner in there too
4) i got water in my gas; use "dry gas" or "heet"
5) vapor lock; loosen fuel cap (this could be an option since every time i top the tank off, this happens, and it usually goes away after i drive it a couple miles. and it's the original gas cap)
6) not enough fuel pressure (if so, then why does it come back alive every other time)
7) sending unit strainer clogged
and don't tell me to trash the edelbrock carb. it's run in this truck for a year, no problems.