Intermittent Starter Motor Pausing Issue
My 1974 Spider (with SPICA) has been having an intermittent "pause" in the starter motor turnover while starting the car. If I were to show the sound it's something like. hmm-hmm-hmm-pause-hmm-hmm-pause-pause-hmm-hmm-hmm and eventually it starts.
So, it always starts turning over but I hear pauses in the cycling. Sometimes, it just starts right up with no pauses and turns over fine.
The big clue is that if it's doing the pause thing, if I put my foot on the gas pedal, it pauses more. Somehow, the accelerator is linked to the pauses and makes it worse.
The battery is at 12.5V and I can start the car with headlights on. I cleaned the battery terminals, neg cable to ground mount, pos cable to alternator thoroughly. I cleaned the switch wire to starter motor.
I removed the starter motor and dissembled it. I removed the brushes and lightly sanded the commutator which looked fine. The brushes looked fine and had plenty of meat left. I lightly lubed the motor bearings. Using a spare 12V battery, I bench tested just the solenoid and it was fine. I bench tested the motor and it was rock solid turning quickly with no pausing. I sanded the starter motor back and the metal gasket and the engine where the starter mounts to ensure a good ground. I reinstalled the starter motor.
The issue still persists.
To add some more info, I know I have an extra rich setting on the SPICA and need to tune it. I see black soot on the exhaust pipe and black smoke when it's cold out.
The compression leak-down test is not great at: 105 100 125 130. That's a future project.
Any ideas before I buy a new starter motor?