I just had another thought.  Has the accuracy of the vacuum gauge been verified?  Have you hooked it to another engine to see if the readings are different?

John - "The Hoosier Hurricane"

These two statements would concern me. Not sure why the shop would have had to adjust the valves a couple of times - I assume this means the rocker arms? On a rebuild this is a once and done kind of thing - I wonder if your valves are not fully seating because the shop is "throwing darts in the dark" at the rocker arm lash. I am not sure how much money you spent on this rebuild but it would be frustrating to find that a shop is withholding key information such as the measurements from the compression test. 

I would think that if you put this engine back under the hood yourself, you would not relish the idea of taking it back out and sending the engine back to the shop. Maybe you could remove the valve covers and check valve lash yourself just to be sure and rule that out as a possibility?

one last item - I know you mentioned that you had 15 inches of mercury on the vacuum gauge. Was that with a steady needle, a floating needle, or a bouncing needle? Maybe I missed that in the thread and all but it would be helpful in discovering your issue.



Daniel Jessup

Lancaster, California

aka "The Hot Rod Reverend"
check out the 1955 Ford Fairlane build at www.hotrodreverend.com

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To answer some questions. Altitude here is 495 feet. Raleigh, NC area.
 The '57 distributor and the Carter carb were already in use, so not new to the rebuild.
Originally, this engine had the teapot carb and the dual diaphragm distributor. Upgrades made by previous owner.
The car lacked power and the compression was low on some cylinders, so that prompted the rebuild.
The vacuum lines for the wipers/heater controls do route through the fuel pump.

Yabut the OP already paid for a complete overhaul.

Or thought he did, anyway.

head surfacing will not contribute to low vacuum,in fact the composition head gaskets are .040 thicker than the stock shimmer gasket, and the pistons on a 312 with correct rods won't come all the way to the top. 57 dist. will have cent advance as well as vacuum,need the correct carb to give correct signal to dist. I am unsure what carb was stock my 57 Merc 312 had a Holley 4v carb. do you have the big fuel pump(that supplements the vacuum) for wipers etc 

Some 56 Mercury’s came stock with a Carter WCFB’s AND a Loadmatic distributor. Changing to a 57 up distributor and leaving the original Carter is not compatible. I use 53 Oldsmobile WCFB’s on my dual quads which work with the 57-up distributor. I use Venturi vacuum for the ignition.
This may not be the problem of the lower vacuum but should be considered. Ted has a write up for converting the Holley to work with the 57-up ignition but not the Merc WCFB. The Merc/Lincoln have a different vacuum system to acuate the secondaries than the GM or Mopars that used the small base Carter’s.
When I was installing the PCV system on my 292 it’s neutral idle vacuum is 19 and in drive 17.5. The vacuum did change slightly with the system as it is a regulated vacuum leak thru the valve.
Just other things to consider..

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

'Ya know something?

If it was me and I needed a complete overhaul, I think I would crate it up and send it to Waco.

I wonder if Ted will run one in and the cost?

BTW- Where the Hell is OZONA, TX?

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Was the distributor installed at the same time as the overhaul?  Maybe the timing at idle is wrong because of different vacuum requirements of the carb vs the distributor.  I can't recall if the '57 Bird had full manifold vacuum to the distributor, or if the '56 Merc provided vacuum at idle.  The Merc had dual chamber vacuum advance pots, so whiscruber carb port is used for the distributor could be a factor.

John - "The Hoosier Hurricane"

Where are you at, altitude wise? If it's in your profile I couldn't find it in the mobile site.

A correction factor is applied for manifold vacuum measurement at anything above sea level. Subtract approx. 1" per thousand feet elevation ASL. This is partly the reason why there is a 3" to 4" spread for "normal" on the gauges.

An engine that "should" ordinarily pull 20" manifold vacuum is most definitely not tuned correctly if it only manages 17", even though the gauge seems to indicate in the green. A mechanic's vacuum gauge can tell quite a lot about engine condition and tuning, but like I said they take some experience and judgment to know exactly what it's actually telling you. My money is on late valve timing, simply because I've seen it cause this, so what else could it be? /s

Seriously though, a quick check of the #1 and #6 valves at TDC and at overlap with a straight edge, and observing where the timing pointer falls in relation to the "0" mark on the balancer will tell you if the camshaft is generally in an advanced or retarded position. This isn't nearly as precise as degreeing a camshaft but it is a quick and easy method that would eliminate the camshaft & timing set installation as a source of the Unpleasantness.

A mistuned carburetor - the idle mixture setting adjustment is good for maybe a full point or so swing or improvement, depending.