Hi, I'm working on a 1977 B-series van with a 360ci and a holley 2210 or 2245 carb (need to verify next time). It starts and idles fine even when cold, and will rev up fine in park, but as soon as you put it in gear it starts to run a bit rough and then once you put it under load it bogs down to the point where it will stall out. I've put a vacuum gauge on it and it will get down to 5 in/hg just trying to accelerate at half throttle. If you really get on it it will backfire.

This van recently had a new fuel pump installed due to a no start condition, and I've verified that it's at least pumping generous amounts of fuel with the new pump. I also recently replaced the voltage regulator and determined that it's capping out at 14v. The old regulator was overcharging and bogging it down at idle. The egr equipment had been removed before my familiarity with the vehicle, or it never had it to begin with.

Just looking for any and all suggestions or wisdom. Looking to do some further diagnosis next time I'm there.

 

First I would verify the timing both initial and total, it’s possible that you have a main jet plugged but I would look and see if the accelerator pump is working.

 

If it's the carburetor I'm thinking of, they had problems with the airhorn warping. With the engine off while looking down the carburetor slowly move the throttle back and forth. The only fuel shooting out should be from the accelerator nozzles (2) one on each side. If it's spilling out from around where the upper (top) of the carb sits on the base, it's warped.

 

All great suggestion..... Also Check it for Vacuum leaks.... Keep us posted.... Cheers

 

I’ll definitely be bringing a timing light with me next time to work that out, thanks for the suggestion.
I took a video of the squirts from the accel pump. I think it’s working and also doesn’t appear to be leaking extraneous fuel visibly but thoughts on that are welcome.
I’ll bring the water bottle and spray for some vacuum leaks as well.

 

Those are the infamous problem carburetors that warp. Yours appears to be working fine, only squirting out the nozzles. The carbs were modified at one point. The air filter screw when overtightened would pull up and warp/bend the upper portion of the carb. The redesigned carbs had the air filter screw go all the way down to the base preventing carb airhorn warp.

Another thing to check while idling is the EGR for leakage. While idling place a vacuum hose on the EGR and suck on it like a straw or if you're fortunate enough apply vacuum by hand pump. The engine should stall out or run really rough. If there's no change your EGR is leaking.

 

Yeah, I was hoping that the egr would be the problem but it's not there, no egr valve or peripheral equipment present and there is a plugged vacuum line, so I think it was removed.

I stopped by the van briefly today with my timing light and determined the initial timing is -8deg at idle and +25 at around 1500ish rpm (I don't have an tach). When I disable the vacuum advance it didn't advance any at the same rpm that the vacuum advance was +25 deg at. Does this indicate a problem with the mechanical advance?

Still to do: measure fuel pressure, look for vacuum leak. Fuel pressure seems okay, I cracked the fitting at the carb and fuel started spraying out in all directions as if there was decent pressure.

 

Your problem is off idle in gear which isn't operating under distributor advance. -8 degrees....... A quick reference check says *5 degrees at idle. I wold bump it up to +5
degrees. While at high idle check if the vacuum line going to the distributor has vacuum. If so, connect the hose to the advance and check to see if the engine speeds up and or if the timing jumps ahead with your light.
The change in timing is pointing towards a jumped timing chain. Electronic ignition shouldn't change timing on it's own without some underlying issue, unless the distributor was loose, excessive play in the distributor, or mistake made while setting the timing.

 

Went back today and determined the timing chain did not seem stretched, timing cover gasket looks new from the outside so I moved to ignition timing. As you said, it should be closer to 5 degrees advanced. I moved it up to 6 degrees as referenced from the workshop manual for this application and the problem went away.

The question became why did it go from driving okay with this timing to driving terrible? The aha moment came when test driving around the block, the first service I did on this van was getting the charging system working. It started having these symptoms afterwards. That should have been a clue, but I wasn’t quite experienced enough to know. I also should have mentioned it in the first post.
The last person to do the ignition timing must have set it when the charging system wasn’t operating. The extra load on the engine was causing the vacuum advance to be too retarded relative to the timing that was set when there was no charging bogging it down. Since higher load=lower vacuum=lower vacuum advance.

 

Sounds like you got it but for future reference. At idle while setting the timing, the vacuum advance should be disconnected with vacuum line plugged with the engine at idle speed.

 

I would suggest... 10* BTDC with the Vacuum advance disconnected at Idle. (Anything under 1000 RPM for idle) and see if that helps....
Also Check the Vacuum reading it you can??? Should be 18" of Vacuum...