I have a 1977 Chevy step van. It has somewhere over 300,000 miles. Been running fine. It has a 1405 edelbrock carb. Last Monday I needed to get some supplies. Started up fine, drove over a mile to the stop sign, it started surging real bad. I had to maintain a high idle to keep it from stalling. It would surge to 1500-2000 rpm, then die, surge again then die. I was able to get it home by riding the side of the road, pushing the throttle, then as it would bog down, I would ride the cluth for another 30-40 seconds, then be able to go again.
Since, I have replaced the plugs, wires, even the gas pump and carb.
HELP

 

Right off the top of my head, you could have either a clogged fuel in, or something sucking up in the gas tank. Is the exhaust "normal" or black smoke?

 

Normal. Plugs were black and damp. I am thinking overly rich, but other than what I changed to try and figure this out, nothing had changed in forever

 

Is the fuel pump electric, or mechanical?

 

Always had standard mechanical fuel pump, then about 3 years ago it seemed to not produce enough pressure at takeoff. I added an electric pump as a booster before the mechanical. since all this has been happening, I have replaced the mechanical fuel pump, no help, then disconnected the electric pump, again , no help

 

I'd strongly recommend you check fuel pressure. That carb needs no more than 6-8 psig. If the electric pump is putting out more than that, I'd recommend a pressure regulator.

 

Thanks, was thinking that way
I wonder why this became a sudden problem

 

This could or would have been an issue since you installed the pump, just more noticeable now. I ordered one for my son in law from Holley, same regulator auto zone advertised but quite a bit cheaper.

 

Does the mechanical fuel pump have 2 or 3 lines from it? You need one or the other, but not both fuel pumps.

 

2 lines