Hello,
The car is a 1966 with a 250 low compression engine and 4 speed. The car fires up fine, and runs great until it starts to warm up. Between when the idle drops and before the oil pressure drops, it slowly develops a miss-fire (particularly on takeoff). At first it is just a barely audible burble, maybe only one. Then as the car warms up it becomes more pronounced. Then it get very noticeable, again mostly on takeoff, evolving into a pretty nasty miss-fire.
I have replaced the plugs (NGK BP6ES) - no impact. Checked and rebuilt the warm-running unit on the IP (figuring the piston may have been seized, and the mixture gradually became too rich) - it was fine, and no impact. I also checked around the engine compartment for loose wires and took a look at the distributor (and vacuum advance unit) which all seemed fine. It's been a while since I replaced the dist cap and rotor, but they looked fine.
If anyone has any suggestions please let me know. I am hoping this is a known problem with an obvious culprit.....
thanks again -- Roger