'73 400 w\ MC 2100. It is in good condition other than it has a burnt exhuast valve and is running on 7 cylinders. It still starts great cold\hot and runs fine, even when cold. Choke spring is new, everything is set up correctly on that end. Here's the problem.

It's getting to be around 35 degrees here in Missouri, and the car starts great with the choke and idles\accelerates well while the choke is on. It takes a couple minutes for the choke to open, and once it is open, the first time I accelerate the engine bogs down and pops out the carb like it is leaning out. After doing that, it runs great from then on. Tonight I pulled over right after it happened to see where the choke plate was at that point and it was all the way open.

My guess was the choke was opening too quickly and the engine was leaning out. The choke spring was at the middle settting, so I turned it to 3-rich like the engine decal says. I bumped the throttle and the choke plate only moved a tad, so I don't think that is going to be helping much. And when you accelerate the choke plate moves a little anyway. So I assume that the engine would have backfired on 3-rich as well.

I rebuilt the carb last summer, float was dead on, carb bolted down tight with fresh gaskets on both sides of the EGR plate, no known vacuum leaks. Any help is greatly appreciated.

 

Happened again today on 3 rich. As soon as the choke opened and I felt the fast idle drop, I tried to accelerate and it bogged down and backfired. After that she was fine. (3 rich is way too much choke anyway. Was on too long.)

Also wanted to rule out the accelerator pump, it's set correctly and it shoots 2 nice streams of fuel. Timing is set to spec as well.

Could this problem be related to the burnt exhaust valve?

 

I would do a comp. test on all the cylinders and see where you are.

 

I get zero pounds on #1, then cylinders 2-8 are all right around 130 pounds. We cranked it over so that #1 was on TDC of its firing stroke and pumped compressed air into the spark plug hole and it came pouring out of the tailpipe.

 

I'd replace that valve, and re ring the engine...