I'm sure this hasn't been asked before...
The 350 in my 1975 Chevy truck has the stock intake and exhaust manifolds on it, and it has the original 2bbl Rochester carb. Originally it had a hole in each throttle plate that caused a lean condition at idle (for emissions compliance, apparently) making the truck run very rough. My dad fixed this back in the 70's by putting a piece of copper wire through each hole to block them off. Ever since it has had a bad off-idle stumble/hesitation/sag.
Fairly recently I had an Edelbrock EFI setup on the truck and it ran beautifully. I took it off to sell seperately (or keep for a potential future project) and now that I've gone back to the carb, the hesitation is back. It happens the worst from a dead stop when trying to take off at a normal (even slow) pace. If I stab the throttle and back off it picks up and goes. To me, that suggests a fueling issue. The problem is, I also notice a pretty bad lug as it shifts from 1-2 and then again from 2-3. That makes me think it might have something to do with the initial timing.
The engine does have a recent cam in from when I had the EFI on it. It is a Summit cam (Edelbrock Performer copy). I plan to check vacuum tonight. It idles great, so I don't really suspect a vaccum leak. Should I be running more base timing than the factory 6-degrees? What else should I look for?
The 350 in my 1975 Chevy truck has the stock intake and exhaust manifolds on it, and it has the original 2bbl Rochester carb. Originally it had a hole in each throttle plate that caused a lean condition at idle (for emissions compliance, apparently) making the truck run very rough. My dad fixed this back in the 70's by putting a piece of copper wire through each hole to block them off. Ever since it has had a bad off-idle stumble/hesitation/sag.
Fairly recently I had an Edelbrock EFI setup on the truck and it ran beautifully. I took it off to sell seperately (or keep for a potential future project) and now that I've gone back to the carb, the hesitation is back. It happens the worst from a dead stop when trying to take off at a normal (even slow) pace. If I stab the throttle and back off it picks up and goes. To me, that suggests a fueling issue. The problem is, I also notice a pretty bad lug as it shifts from 1-2 and then again from 2-3. That makes me think it might have something to do with the initial timing.
The engine does have a recent cam in from when I had the EFI on it. It is a Summit cam (Edelbrock Performer copy). I plan to check vacuum tonight. It idles great, so I don't really suspect a vaccum leak. Should I be running more base timing than the factory 6-degrees? What else should I look for?