Put a clear filter in and look in it right after the car has been driven good and hot. You will see the rolling bubbles.
A plastic spacer plate, 1/4" gasket, block heat cross-over in the intake, insulate the fuel lines near anything hot, fresh air, remove insulation on the hood, heat sheild for the carb, return line. Any of the above will help.
If you ever drained your coolant and didn't bleed the system, you will probably not have heat in the car and the engine will over heat. This is another form a vapourlock. The air pocket gets trapped and coolant can't flow past it under pressure.
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82 Mercury Capri 302.
Comp. Cams
Tremec 3550
3.73's
12.8@106 N/A
Kevin's Capri