I was checking the timing on my '56 292. I'm running a recently rebuilt t-pot carb with a modification to run a single vacuum line to the vacuum advance. I have a distributor from a '62 Y-block and a single vacuum advance. When I adjust the timing with the vacuum line disconnected to the I think "3 deg" mark on the damper and then reconnect it after it's sets it runs poorly. It advances quit a bit with the line reconnected at idle. When I set it to the spec'd degrees with the line connected it runs much better, like it should. How much should the vacuum advance advance the timing at idle? It seems too much which is causing a poor running condition as specified in the shop manual.


~DJ~ AKA "Bleach"
1956 Ford Fairlane Town Sedan 30K original miles

I'm fairly certain the index mark on the damper is correct. A few years ago I had the valve covers off to check the valve lash and to verify installation of the distributor. In the slim chance it's off, it would be very minimal. Bolh valves were closed and the #1 piston was at TDC checked repeatedly with a stiff wire in the plug hole. Compression check was with normal range back then. Dwell was OK on the meter. Points were showing closer to bad than OK. I have a spare set of points I can always swap.
I think it will take a little finesse to sort it out. I'll see about lowering the rpms a little more closer to 500 rpms. I've always adjusted my carbbed cars in the past to idle slightly higher in the 600 to 700 range mostly for colder weather driving.


~DJ~ AKA "Bleach"
1956 Ford Fairlane Town Sedan 30K original miles

If I read your post correctly you said the distributor was getting its vacuum source from a spacer under the carburetor. Pretty sure that would be manifold vacuum which will immediately advance your timing. 

Duane