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I'll check it at the line going to the vacuum advance instead.

HH56 wrote:
Quote:

I'll check it at the line going to the vacuum advance instead.

That may not work either. Packard usually used a port on the carb for the timing advance that had an opening in the carb above the throttle plate. That is why you can usually check and set timing at idle without disconnecting and plugging the advance line. When the throttle is near closed like it would be when checking vacuum at idle the measurement at the advance port will be very low if not near zero so the advance mechanism is not moved. Some have for various reasons re-plumbed the advance to use the port at the manifold instead of the carb and if your car is one of those then it would work.

If it was checked by removing the hose connecting to the fuel pump vacuum outlet port and inserting the gauge in the hose or tubing end, that should be a direct line going to the junction block on the intake manifold. As long as the hose and connections are tight it should be a reliable spot for a reading.

HH56 wrote:
It is except there is a check valve in the junction block at the manifold that connects to that hose. The valve is there to keep a residual supply in the canister to be able to operate the brakes a time or two when engine is off. Not sure what the opening spec is for the valve but I doubt the vacuum reading after the valve would be much different than the reading before it you would get if you checked at the fuel pump hose..