Vacuum Advance Problem

Sounds like its advancing way to early or easily. Check your springs? Make sure your wires aren't getting pinched when advancing. You can operate that advance with the dist cap off by putting a hose on the dist port and sucking on it to see whats going on. Is it backfiring thru the carb

Passenger side is ported vacuum, so when the throttle is opened it puts vacuum to the distributor. Ser the timing with the hose disconnected at the minimum spec per manual and start from there.

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Some aftermarket vac canisters are adjustable. Check your base timing like above, then see what the total mechanical advance at rpm is from there. If the canister has been bad long enough, it could be tuned for advance without vac. You'll want it for highway and cruising. So third, make sure what the total advance is with the canister plugged into the right port. If an Allen wrench in the tube (like on an HEI) does not do it, they are sometimes marked with how many degrees and can be swapped. Or a blocking plate allowing partial advance can work.