[middletown]

I'm gonna go a different direction on this one. Have you checked for a restriction in the fuel at the tank? Rust and garbage can build up at the outlet and still allow enough fuel though to run but as more fuel demand (time or acceleration) is added the car will begin to starve for fuel. Allowing the car to idle or sit momentarily often temporarily helps the issue so as you worked to solve the problem fuel seeped by the blockage and filled the bowl and line so when the next test drive started all seems fine. Since the car is going lean the choke would "seem" help out and a lean mixture is going to lead to higher operating temps. To check this disconnect the fuel line at the carb or somewhere below the tank and using a rubber tipped air nozzle connected to your air compressor carefully blow back up into the tank to disperse the blockage. If it works clean the tank or ignore it until it happens again; if you really get it cleared it usually takes along time to build up again.

Just a guess,

Good luck,

Joe