Yes.  While peeeot has already mentioned that any evidence of gasoline or wetness present on the vacuum side of the diaphragm is a good indicator of either a leaky gasket or ruptured diaphragm, there are testers available that will test the power valve for both diaphragm leakage and what the actual Hg opening point actually is.  Here’s a picture of the power valve tester I use.

 

Lorena, Texas (South of Waco)

Thanks for the info. I will check them.





Is there a way to test the power valve?





It is possible that the springs were completely compressed before the idle screw fully seated. I will check to make sure.







I will add that to my list of things to test. I probably could also hook my vacuum gauge to wherever the transmission vacuum line goes into the motor for my vacuum test.



Thanks for all the tips and information.

Dave Coleman

1962 Country Sedan

http://www.62ford.com/

I don't know what the transfer slot is. I also don't know what you mean by closing off the idle screw. If I can figure out what that means, I will surely try it.

Dave Coleman

1962 Country Sedan

http://www.62ford.com/

The air bleeds are not that sensitive to height changes and even if they were, the float level could be adjusted in which to compensate.  A single gasket for the venturi assembly is only marginally thick (0.025”?) so double gasketting in this case is not an issue. 

Lorena, Texas (South of Waco)

According to carnut.com, your initial advance should be set at 12* with the automatic transmission for a '62 292. Dwell angle is 26-28* (point gap of 0.015"). I would assume the idle speed to be approximately 500 rpm with the trans in drive.



As for your question about the power valve, it is not an idle control device, but since one side of the diaphragm is exposed to manifold vacuum, the potential exists for unmetered fuel to be drawn through a leaky diaphragm or gasket. Such a leak would enrich the mixture at idle, perhaps enough so that no additional fuel is needed from the actual idle circuit, which could explain why the engine is able to run with the mixture screws closed. It would not run as smoothly as it should in that case, however, because the idle circuit bleeds air into the fuel stream and mixes it a bit before it ever gets to the mixture screws. A leaky power valve would not provide that "pre-mix" so the mixture uniformity would suffer as would idle quality.



Have you verified that the mixture screws are in fact fully seating?



Assuming your trans has a vacuum modulator, the transmission shift qualities probably wouldn't be affected by the kind of vacuum leak we're talking about here, but if the modulator is leaky, THAT could affect the carb adjustments. It'd be worth plugging the modulator vacuum line just to check whether it's a factor.




1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

It may be too much of the idle transfer slot is exposed. Take the carb off and close off the idle screw so the transfer slot is square with the throttle blade. Install carb again and try adjusting mixture screws.

A vacuum gauge is a great tool for diagnosing engine condition.If you still have the printed instructions there should be examples of various readings on the gauge.Sounds like you have the idle speed screw in the correct range.

  

Thanks for all the tips. I would like to clear up a few things. The original carb that I am using has the original venturi assembly and original jets. I have two power valves from two different kits and neither solved the problem. From the description I was given regarding how the gasket sits on it, it is not a Holley power valve. The power valve is dry under the cover. The idle speed adjuster screw was turned less than one turn after contact with the throttle shaft lever. The car idle rpms are very low, probably at the correct setting or even a little lower. When I come to a stop, I can barely tell the engine is running except for the slight roughness. The float level is set perfect, but I still need to check the gas level in the bowl. I have checked for leaks by spraying wd 40 around the carb base and the throttle shafts, but will try it again with starting fluid. I am positive that all the circuits are not clogged.



So now I will recheck for a vacuum leak by using starting fluid instead of wd40. To keep the mist from entering the carb through the top, I will put the air cleaner housing on and then spray the base. I will also check the manifold vacuum. I have a gauge. Where is a good place to take the reading. This is a 62 292 engine if that helps. Could burnt valves cause bad vacuum? I don't know the condition of the valves. I'll check to see if the venturi assembly is not warped. I will also check the timing, dwell, and set the idle rpm to factory specs. Does anyone know what that is?



It might be a few days before I get all this done because of my job, but I will do these things. Even though it is running pretty good the way it is, I want it to be right. I am learning a lot with your help, but what I don't get is what does the power valve have to do with the idle? I thought it only was used during acceleration. Also, if there was a vacuum leak, would it affect the transmission? The transmission shifts perfectly and the kickdown also works perfectly. The car has manual brakes, so I think there is nothing else using vacuum.



Thanks for all your help.

Dave Coleman

1962 Country Sedan

http://www.62ford.com/

A note about checking power valves that I didn't see anyone else mention: when you remove the power valve cover it should be bone dry with no evidence of fuel having been present. If fuel moisture is present it means leakage past the power valve gasket or diaphragm. I have used GP sorensen gasket kits almost exclusively and I know there were a couple of power valve gaskets included; not all of them would work properly with the actual valve included.



Perhaps you covered this when you say you sprayed carb cleaner through every opening, but when rebuilding I like to spray water through the paths air and fuel should take. If I don't see a nice stream of water coming out of anyplace it should, I don't move forward until I do. Following that up with compressed air is a good idea of course. One time I had an air bleed on a 4100 that I had to remove the top plug to clear up.



Ted: wouldn't double-gasketing a booster assembly effectively raise the location of the fuel holes relative to the level in the bowls, and thus affect the desired float setting? Or is it not that sensitive?

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

As has been mentioned, checking for vacuum leaks is at the top of the list.

 

As a general rule, always go with the jets that come in a given carb as a baseline.  Jets sizing is more of a function of carb size and air bleeds and not so much as based on the cubic inch.

 

The venturi assemblies in the Autolite carbs are notorious for becoming warped due to over-tightening.  Because the air bleeds for the idle mixture is at the outside edges of the venturi assemblies, the idle mixture adjustment ends up being compromised when warpage is present.  If you do check that for straightness and find the gasket surface is less than straight, then the simple fix for this is to put a double gasket under the assy.

Lorena, Texas (South of Waco)