I think I mentioned before that both mufflers are installed backward. There is definitely still exhaust flowing through them. I have assumed this could not be a significant factor. Should I reconsider?

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

peeeot

"Pete, the potato in the exhaust will have a similar effect to what?"

If the exhaust gas can not get out as fast as the carb lets in air the car will stop running with a slow lingering death. Usually the muffler will blow out first. Pete

This was common on the cars of the early 70`s with catlytic converters when the inside collapsed and restricted the exhaust. The burned exhaust gas is mixed with the air/gas mixture in the cylinder and the result mix is beyond the ratio to ignite. EDIT

The spacer is the original fiber type.

Pete, the potato in the exhaust will have a similar effect to what?

I am finding now that the longer I let it go it gets harder and harder to keep it running at all, forget about going into gear. I have to prime it and put the throttle on the top step of the fast idle cam to get it to start; then, if I leave it on the second step around 900 RPM it will stay running indefinitely, with occasional hiccups. If it is allowed to idle at 800 rpm it will quit after a time. It can't run at 600 rpm at all when it's hot. It acts lean, but if I open the mixture screws at all it slows down and the plugs get sooty AND it will stall. I lowered the float, no help. I didn't go through the valve adjustment again but the vacuum gauge needle is perfectly steady except when it hiccups. Plus I have been through that adjustment many times already. I opened up the new carb, whose float bowls were immaculate prior to installation, and they remain spotless, which is to say that there is no evidence of trash or sediment getting in, and I'm positive that all carb passages are completely clear. All of the parts (nozzles, jets, metering rods, etc) are correct.

This thing MUST be POSSESSED. Maybe I need to start pushing it around a junkyard and watching it fix itself.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

Is it a metal spacer or fiber type spacer?

  

I NEVER did this but a potato in the exhaust will have a similar effect. Pete

Pete,

I removed the plate but left the shaft and spacer. The shaft was completely locked up. If there were a crack in the intake between the carb passages and the exhaust crossover, would it be visually obvious?

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

peeeot

Since your issue seems to be heat related, have you checked the passenger side exhaust manifold down pipe for a stuck exhaust damper? Very common. Pete

I've wondered about that. Figured if they were a problem it would show up in the compression test, but maybe it cooled down enough in the time it took to pull all the plugs and install the tester. Also figured it would show up on the vacuum gauge as a steady dip. Still, I know the rocker shafts are pretty worn so it's worth another look.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

Have you checked the valve adjustment, perhaps some of the valves are set too tight?

Frank/Rebop

Bristol, In ( by Elkhart) 

Chiggerfarmer, thanks for that suggestion. I tried dropping the floats a little today and I noticed a change but not an improvement (nor a worsening, per se). Perhaps I'll try dropping them even lower soon.

oldcarmark, yes, I have the original phenolic spacer in place.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive