Dark Horse,
Your getting close to the problem, that choke plate has to be fully open when the car warms up. What I do is turn the plastic dial towards lean then start the car and see if it goes full open when warmed up.
If this does not help after turning the dial towards lean then the choke thermostat is not working. It is a spring that moves when either warm or cold. If this choke plate is staying almost closed the mixture will be too rich and foul out the plugs.
And what in the hell is this motor mount thing?
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69 351W Sportsroof deluxe