Symptom: when cold the car starts normally with an idle speed of 1K. A couple of minutes later the idle steps down to 6-700 and the car runs properly. If I run the car for 10-15 minutes, turn it off, and then restart the car the idle speed stays at 1K and does not step down. Acceleration is not smooth (lots of hesitation) and after a couple of painful minutes the engine stalls. When this happens the car is very difficult (sometimes impossible) to start. The fuel pump ticks normally when the engine is running and the glass bowl is full. There is spark from the coil.
Peter Russo
1963 Mk2 3.8
Engine has around 5-6K after full rebuild.

 

When you say you run the car for 10 to 15 mins. do you mean idle or driving? Glass bowl should not be full. Check your plugs and float levels/?

 

The car is being driven, albeit very close to home and at neighborhood speeds (20-25 mph) for the 10-15 minutes. The plugs are not fouled. I'm not sure about the float level. I haven't taken the carbs off. Is this the logical next step?

 

With out knowing if your car has an automatic choke or manual, it's pretty much impossible to give you definite answer.
Could be the floats are not adjusted properly as George says, but it sounds like your choke is coming on again after the car is warmed up.

If you have the automatic choke with the otter switch that's controlled by the coolant temperature, I would check that first before going after the float levels and removing the carbs.
After the car runs, warms up and steps down to a normal idle (as you say), open the hood and disconnect the wire from the otter switch while the car is running.
Now see if the symptoms come back. (leave the otter switch wire disconnected)

Note that the wire to the otter switch will have to be re-connected to start the car from cold.
Most replace the otter switch with a toggle switch under the dash.

 

The car has an automatic choke. I will give this test (disconnecting the otter switch after the step down) a try in the morning. Thank you for the tip.

 

Hello JeffR1, the issue has been sorted and the culprit identified as a faulty Pertronix ignition.

 

Glad you figured that one out, I bet that wasn't easy, how did you determine it was the Pertronix ignition ?

I was never a big fan of that aftermarket stuff and this is why.
It's like depending on these debit machines in the stores, they work 99.9% of the time, but one still has to carry cash around for that .1% when things go wrong.