A trick I use to hunt air leaks is to use some carb cleaner spray.
1st get your engine to idle at the lwest setting it can without dieing. Use the idle speed screw to set it.
Plug all vaccum ports to eliminate a leaky vaccum advance and winshield wiper motor. If the idle picks up once they're plugged you've found your leak.
If no change, take the carb cleaner and spray short burst of spray directed at all sealing joints one at a time.
Where the carb bolts to the manifold, where each intake manifold runner bolts to the head and around the throttle shaft on the carb. If the idle changes at any location you've found a leak.
Remeber to take short bursts while paying very close attention to the engne speed and sound. There should be no change if theres no leak.
I've used this method successfully on other engines and should on a stovebolt 6.
Good luck
Dave
