SBC 305 help!

Howdy folks!

I got my hands on one hell of a beautiful '85 El Camino with a small block 305 v8. I need some help with it, I’m stumped!

When I’m out driving, if I gun it, or sometimes even if I just let on the throttle too sharp, the engine will sputter and fail to rev until I back off the throttle. Stopped, in neutral, I can rev the engine all I want. The engine also has a tendancy to diesel when I shut it off for about 2 to 3 seconds intermittently. Lastly, I know it’s running rich because I can smell gas, it’s getting poor MPG, and I was working on the exhaust and some of the new parts I put on are already coated in black soot.

Could all that be from the engine running too rich? If so, how much would the average mechanic charge to tune a Rochester 4bbl? I’m good with cars but this is my first carbed engine and it’s all new to me :-/

The problem is the carb. You need to have it re-built. It sounds like you have an internal leak that is causing the engine to run rich. Find an old-school mechanic. He’ll fix you up.

You could have a choke that isn’t opening too. Check the vacuum lines to be sure they aren’t cracked at the choke pull-off. If your choke thermostat hasn’t been changed, you may need a new one. The bimetallic spring stops working after about fifteen years. There are lots of carburetor instructions for the Q-Jet. It’s a little vacuum diaphragm sometimes mounted high on the carb. To prevent stalling, make sure the stove pipe is still on the car, from the exhaust stove to the air cleaner. When an engine is warmed up, a rich fuel mixture could cause the after-run.

A Rochester 4 bbl on an '85 El Camino? Well, that can’t be original. I’d be concerned about what the carb came off of. The 305 isn’t a very large engine, and you may very well have WAAAAYYYY too much carburetor on it.

There were several fuel delivery options on these vehicles but yours more than likely has the Quadrajet carb.
If the carb is running rich then the first thing you need to do is remove the air cleaner top when the engine is warmed up and make sure the choke flap is wide open.

If the flap is wide open then it’s not likely that any amount of adjusting is going to cure this problem and it’s time to overhaul or replace the carburetor.
Chances are the dieseling is probably related to the previous owner misadjusting the carburetor idle screws. Other potential causes of dieseling could be an air leak or ignition timing that is too far advanced.

An internal leak in the jet well plugs could be causing the rich running. (Assuming a Quadrajet carb here, which is the norm.)

a car this old the carb is most likly to worn out. first find some that knows how use vacuum gage and kknows how to adjust a carb chock. order a new carb or a rebuilt one from a good store . you will get the corret carb replace any vacuum lines also. start with cold adjust first
make sure engine is cold. let heat up then adjust fuel jets. you might have to do or check adjust the second day to make sure. thank god for fuel injection. in the old days we had to keep a car two or three days just to adjust the carbs . and twice a year remember the chock needs to be adj for hot or cold weather. cars from south would not run in the north in winter. it is nice to speak to an old fart.