Next thing to check is if the camshaft has become flat. Pete

Previous suggestions are all good. More thoughts…

The ’55 Holley 4000 has a small, mushroom shaped, vacuum diaphragm on the passenger side of the carburetor base toward the front of the carburetor. This device is a ‘spark control valve’ and is part of the distributor vacuum advance system. Look for it directly below where the air cleaner housing sits, in front of the vacuum secondary diaphragm throttle shaft connection, and adjacent to the idle mixture screws. IF the diaphragm in this unit is bad, it will cause a vacuum leak.

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Previously mentioned… the diaphragm in the vacuum control canister attached to the distributor could be defective. Potentially, it is 59 years old! Again, bad diaphragm, vacuum leak. The ignition advance on the ’55 ‘Bird is TOTALLY vacuum controlled.

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Wherever the vacuum take-off for the windshield wiper ‘motor’ is located on the intake manifold, it leads to the fuel pump. Weird, huh! In addition to drawing and pumping fuel, the ’55 fuel pump has a second diaphragm that boosts the vacuum to the windshield wiper ‘motor’. Although you replaced the pump, the diaphragm that does this could be defective, again causing a vacuum leak. Block the intake manifold vacuum take-off to rule this second diaphragm out.

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Holley 4000 carburetor shafts are prone to wear more than some. This can cause a vacuum leak,also. On the ’56 Power Pack set-ups and the ’57 ‘E’ set-ups (2x4 carbs), high idle speeds that can’t be brought down are often the result of worn throttle shafts or shaft bores. Squirting some 30 weight oil on the ends of the primary and secondary throttle shafts will rule this out if the idle speed drops.

NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

Thanks for the suggestions and continued support.

• I have been checking the vacuum by disconnecting the line that runs from the intake manifold to the fuel pump and attaching my gauge to that line.
• I have blocked off the brake booster, no change.
• I have disconnected the vacuum line to the distributor and didn't see a change. When connected, the timing does advance with RPMs.
• The mushroom shaped diaphragm on the side of the carb seems to move in about 1/16" or so when revved.
• Vacuum is idle speed and ignition advance dependent. Initial advance is somewhere around 25 degrees. With the idle at ~750 RPMs, vacuum is ~7"hg. At 1000 RPMs vacuum is between 10 & 11"hg.
• Placing the car in gear will drop the idle from 1000 to about 450, barely enough to keep running.
• All the valves look to be opening the amount, but I have not measured yet to see if they are within spec.
• The car seems to run best at ~25 degrees initial advance. Move it much further and it detonates under a load, retard it and it's really sluggish.
• When the car is idling, there's a steady stream of fumes coming from the road draft tube. Is this normal?

I haven't checked compression since I have adjusted the valves, but plan on doing that this evening. Also, I will do a dry and wet compression check to see if it's a piston ring issue. The first test I did was dry and the cylinders were all in the 110-128 range.

At this point, I think that the problem is either the camshaft orientation or an issue with the rings.

The motor looks like it's been rebuilt (I know that the heads have been), but that doesn't mean anything. Maybe the engine assembler installed the rings wrong, or maybe they are all stuck because the car has done a lot of sitting after its restoration. Or maybe it was only painted and not rebuilt.

The fact that it needs so much advance makes me think that the timing set may have been installed wrong. A previous shop had pulled the timing cover to inspect this, but it's a foreign car shop, so their Y block experience is probably very limited. It could be they were looking to find the dots on the gears lined up at 6 & 12 o'clock like every other V8 that I've ever worked on. If I understand correctly, the dots on the gears should both be around 3:00 with 12 links between them.

Sorry for the long post, but I wanted to keep those of you who have been helping me up to date.

Thanks again,
Bobby

Bobby:

There should be 12 PINS between the dots on the timing gears, 6 links. My latest thought is that maybe your vacuum gauge is lying. Have you tried it on another car?

John - "The Hoosier Hurricane"

12 pins, not links, thanks. I did try the gauge on my old Nissan truck and it is rock solid around 22", just like you would suspect.

Here's a link of it running. The valves sound much louder in the video than they do in real life.

http://www.youtube.com/watch?v=vOMI_Hp88oE&feature=youtu.be

It's hard to tell a whole lot from that video because of the way the microphone picks up sound and the way the frame rate can interfere with the movement of the vacuum gauge. Judging as best I can by the exhaust sound, something is definitely wrong if it is a stock cam. The 15" hg at 800 rpm is not unusual for a mild cam, though I would expect your compression pressure to be much higher.

In an earlier post, you asked "While I do think the carb has issues that need attention, could it be bad enough to make the manifold vacuum half of what it should be?" Yes, a poorly tuned carb, either due to wear or the tuner can cause all sorts of problems, including decreased vacuum. However, the low compression does still point to another issue. Given that you don't know much about the engine, I think it is probably just worn out and getting to be time for a proper rebuild.


Lawrenceville, GA

That's actually about 6" of vacuum in the video. The numbers on the outside of the dial are metric.

Well, tore off the front end and didn't find what i was hoping to find. The timing is oriented as it should be, so I guess that means it's the rings. I had been contemplating pulling the engine anyway to repair leaks and freshen up the restoration, so why it's out why not freshen up the engine so that I know what I have.

Maybe it's just the camera angle, but that chain looks a little loose to me. Maybe during the overhaul the main bearing bores were align bored, which moves the crank closer to the cam.

John - "The Hoosier Hurricane"

I haven't measured the play in the chain with a ruler yet, but it looks to be about 1/2".