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

Ordinarily there won't be any additional advance when checking the ignition timing with that setup you describe, but that is dependent on the engine RPM. Once the throttle butterflies open up even a little there will be some vacuum applied to the vacuum advance diaphragm. Factory idle spec was something like 450 - 550 RPM. Anything much above that will start to show significant ignition advance above the base mechanical setting. Make sure the crankshaft damper ring isn't defective, these are very often slipped off their "clock" and make setting the initial timing very confusing.

The additional ignition timing advance provided at a higher idle RPM is probably why most people like their idle RPM increased over factory, it smooths out audibly and runs noticeably cooler. In this situation 20° BTDC or even more at idle wouldn't be unusual. Remember there is no engine load at idle and this won't hurt anything. It will not pass any sort of smog testing however.

If the distributor vacuum advance diaphragm is defective then it will introduce a vacuum leak and run poorly, be sure to check for this. A lot of people like to run 10° to 12° initial or base timing regardless.

I'm also running a PCV valve. I blocked off the crank vent and used a T-Bird valley pan with a special adapter that looks like a small tea pot. I have a plate under the carb that the line gets vacuum from. I thought it was the source of my idle issues but I confirmed it wasn't. I have the idle set at about ~650 rpms in drive. Anything lower it seems to want to stall. If I set it to spec in the manual as I menetioned above, I have to set the idle much higher and it still stalls. It runs way much better and smoother setting it with the vacuum line attached. The damper doesn't show any signs of it ever slipping. It's the original engine and it only has a little over 30,700 miles from new.


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

If your running a stock 56 Holley with a 62 distributor they are not compatible to give you the best drivability. The carb was built for a loadmatic distributor not centrifugal/vacuum. Ted Eaton wrote an article on how to modify it to work and I believe it’s on his website .. Eaton Balancing.
Using ported vacuum for idle normally will have no effect when you are idling and you should see no change on your timing mark with it plugged in. Personally I like ported for the lower RPM idle but others prefer manifold. My stock 56-292 has the ignition timing set a 10 and idles fine with no hesitation when warm. I too use a PVC system and a PVC replacement valve for a 1961-1964 Ford/Mercury which is threaded into the intake manifold on my engine. My engine has 10k on it. 


56 Vic, B'Ville 200 MPH Club Member, So Cal.

The carb was modified by a reputable builder earlier this year so it has the proper port for the distributor. It's just going to take some more adjusting. The carb is very easy to adjust as is everything else at this point.


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

The crankshaft damper has an elastomeric (rubber) sandwich between the heavy inertial outer steel weight and the cast portion, it is probably more a function of age than mileage that causes them to fail. It is very common (even if it hasn't slipped they are no longer functional). These should always be replaced or rebuilt as part of an overhaul.

If the timing marks have moved off the keyed index "0" TDC, setting the timing accurately isn't going to be practical. This would be the first thing to verify, simply to remove this defect as a possibility, particularly for anyone trying to help sight unseen. A "piston stop" tool is inexpensive.

Can also check ignition timing by way of inference, using a mechanic's vacuum gauge. A healthy stock engine in good tune at sea level will always pull 19" to 21" of steady vacuum at factory idle with ignition timing set to factory specification, if it doesn't, there is a defect somewhere in compression, valve timing, ignition timing, vacuum leaks, misadjusted carburetor, etc.

Engine should idle and run reasonably well with vacuum advance disabled and set to 450 - 500 RPM. Also want to see that it advances the ignition timing smoothly up and down the RPM range. Most Y-Blocks like plenty of advance, 36 to 38 degrees on pump gas should run fine. With vacuum advance connected 50 degrees BTDC or more would be typical on flat ground steady cruising.

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

Sorry I must have wrote it confusingly. The PCV is connected to the spacer. The vacuum advance is connected to a modified port on the carb  like the one done on Ted Eaton's page. https://www.eatonbalancing.com/2013/03/02/modifying-the-holley-teapot-four-barrel-carb-for-late-model-distributors/


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

3° BTDC ignition timing should run OK, and it should also run OK with vacuum advance connected, regardless. In this case it sounds a little like the vacuum advance diaphragm is leaking, but it's difficult to determine from just a description sight unseen.

20 or 30 degrees timing advance at idle would not be "too much" as far as that goes, something else is going on to cause the poor idle. For test purposes disconnect and plug the vacuum advance port on the carburetor. Set the initial timing to 12° and see how much manifold vacuum the engine is pulling. It should idle smoothly enough and drive OK as well. The mechanical timing curve is always sorted first, before connecting and messing with the vacuum advance.