Don't run well when warmed up

I did the check with the dwell meter and the reading did not change at all when I revved the engine.

Dwell angle is 22 degrees with or without vacuum. The dwell meter reading does not change as I rev the engine up in either case.

The shop manual specification is 21 - 30 degrees, but perhaps 22 degrees would work OK on a new tight motor. 22 is perhaps too low for this old chief. The odometer numbers don't line up straight so probably gone around once. I will reset the points to as close to 30 degrees as I can get. I also appreciate the idea of checking the compression for pressure variations and the condition of the spark plugs as well. Thank you. Will do later.

Hi there again. Still trying to make this Pontiac run as good hot as it does cold. I have done some further testing on the car to provide more details on what I am up against. I replaced the points, condenser, and rotor and reset the dwell angle. I now have 28 degrees without vacuum and 26 degree with vacuum. I did a compression test (dry) and got a range of 95 - 110 psi. I put a timing light on it and the timing is good and the vacuum advance does advance the timing when cracking the throttle. I did also replace the spark plugs just because I could. The vacuum at the distributor, idling is at 3 inches of vacuum and climbs to 20 - 22 inches of vacuum when revved up. Still it starts and runs like it should until the temp gauge get near running temperature. ???

I don't have another carb available. The issues with it running badly were identical before and after the jet enlargement. I'm not sure how much he opened it but, but it wasn't a lot This car was supposedly running until he was out in it and it started running bad. he got it home, parked it in the garage and let it sit for a couple of years.

Back again, more things to check. The exhaust smells like normal old car exhaust and no blackness to it. The engine runs really well without the gallop of one running too rich. I did add an inline metal filter so I could make sure no grr was coming through the line and it continues to be full and clear. The vacuum line to the windshield wipers had been re-routed to use manifold vacuum, probably because the fuel pump was messed up, but after rebuilding the pump, I changed it back so the wipers are now using fuel pump vacuum. The choke is the original automatic and it works surprisingly well. I have it adjusted so it is wide open when the engine is warmed up. I checked the fuel pump output and it is pumping out a good amount of fuel. Would fill a water glass in several seconds.

I might be able to say that I believe it is running a bit better. I seems to have a dead spot at a particular RPM where it runs bad and rejects the idea of revving any further, but if I crack the throttle and the accelerator pump cycles a couple of times, it will rev up above the dead spot. I think this is some progress. I let the engine warm up and spritzed water at the intake manifold all over to check for vac leaks. I prefer to use carb-clean for this test but didn't really want to burn the car to the ground. Heard no indication of a leak.

An old mechanic up the street said they used to have trouble with the old flathead motors because they had no upper cylinder lubrication except for the lead in the gas. He thought maybe because the car had been sitting, the valve guides may have been tight and unlubricated making the valves a bit sluggish closing when hot and at higher RPM's . He said to add some two-cycle motor oil additive to the gas and it might help. I did and a change isn't jumping out at me but, maybe it is running a bit better and will eventually work out of it. Watcha think ??