Power valve

[Ford coupe]

Can I test the power valve on a 55 Ford 272 carb?? Carb is apart for cleaning and I have a leak down the throat after I switch it off so was told it could be the power valve... Thanks in advance..

[scicala]

I assume you are talking about the Holley/Ford 2 barrel carb and not the Holley teapot style 4 barrel carb. (272's came both ways in '55).
If it is wet on the vacuum side of the power valve when you separate the bowl from the base, then the power valve is leaking through the diaphragm.
I have a fixture I made to check them and apply vacuum to make sure they stay closed. I think somebody makes a fixture, but not sure if they do, or who makes it.

Sal

[Bob-93021]

I just got done rebuilding the 2 barrel on my 47V8. This carb is basically the same as a 55. The carb would drain its fuel in about 4 hours. Had to remove air cleaner and dump fuel down carb if it sat a day or more. I took the carb apart because of leaking power valve and I paid extra attention to the power valve upon assembly.
The power valve in the kit had sort of hat over the diaphragm. I dry assembled valve to body with gasket. I then fitted up the carb base (no gasket) and saw that the power valve was interfering preventing a good mate. Maybe the gasket between main body and base would seal? What I did was grind off the hat over the diaphragm. Again I did a dry fit and it cleared. I assembled the main body of carb with power valve installed and did not bolt it to the base yet. I filled the float bowl about half way up with gasoline and let it set 5 or 6 hours. Since it was not wet under the power valve I went ahead and assembled carb. Car is not on the road yet, but it does seem to idle and respond just fine. A bit long but hope this helps - B

[Ford coupe]

55 272 carb with Ford written on it..Filled fuel bowl up to hole that drains into pump well and let sit overnight...Went down about a quarter inch and the only place I found some dampness was on the end of the nozzle bar and even then just a bit of dampness on the end of my finger no dropps.. so maybe could be evaporation??

[Daves55Sedan]

If you look down at the bottom of that bore where the power valve goes (with power valve removed) you will see a little steel ball held in a hole by a spring clip. If that ball is not seated good, it can drain all the gas because the passageway for fuel from the float chamber to the power valve chamber is down at the bottom.
Yes, if it is a 2-BBL carb with Ford on the right side of the float chamber, it is a EBU carb. They were only used for two years ('54 & '55). In '56 the 272's had a similar carb with larger intake bores and slightly larger air throat. That was the last year for that style of carb.

[Daves55Sedan]

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Originally Posted by Bob-93021

The power valve in the kit had sort of hat over the diaphragm.

The purpose of that "hat" is to provide stability for the rubber diaphragm as it is sandwiched in between that hat on top and a washer/rivet on the bottom. They make the "hat" as big as possible while still allowing room for just the angled portion of the rubber to stick out.
If the "hat" were smaller, it could cause a slight hesitation upon acceleration because more of the exposed rubber would deflect with the movement of the power valve actuator and more importantly, the power valve rubber diaphragm would begin to break off around the hat prematurely due to the additional amount of rubber being subjected to up and down movement (deflection).
As Long as the power valve can be inserted into the bore and pushed all the way down without any interference from the "hat", there should be no need to whittle it down to a smaller diameter.
I'd be more worried about the power valve rubber being too loose in the bore, but sometimes you can remedy that by stretching that round spring underneath the rubber diaphragm. And for that matter, some can be too tight (which causes you to push on the gas pedal more just to get going). If the valve rubber is too tight in the bore, I don't think there is anything you can do besides get a power valve that fits properly. I've seen it both ways.

[WRA]

I purchased the Moroso 62295 Power Valve Tester few years ago. It's a wonderful tool. It's also about $50 so it may not be worth it for a one time job.

[scicala]

Ford Coupe never said his power valve had a "hat" on it. Also, the hat Bob-93021 is talking about, I'm pretty sure is on the other side of the power valve (large end with hex).

Also the bore with the check ball and wire clip that Daves55Sedan referred to, is the accelerator pump bore, and has nothing to do with the power system.

Sal

[Ford coupe]

OK guys got it I hope..Now the power valve was indeed leaking but in such a small amout that it was evaporating before it got out on to the metal part of the valve so when I looked up in to the valve I could see that the neoprene was all wet with gas hence the small drainage from the bowl...Put in new valve and no more draining of the gas in bowl and car runs fine but had to turn idle down a bit..Now some confusion regarding this carb the little steel ball check valve is at the bottom of the accelerator pump bore and really is altogether separate from the power valve but if it is not sealing it will also allow carb to bleed off..So thanks so much for all the good info..Harry

[Ford coupe]

I would bet the tester WRA mentions would screw on the end of the valve allowing one to put pressure or vacuum on it to find if the neoprene diaphragm id leaking My 5 cents worth

[scicala]

Yes, once vacuum is applied, the leak gets much worse compared to just gravity when the engine is off.

Sal

[Daves55Sedan]

Sorry about the confusion. Yes the power valve is that thing that screws in under the main body under the float chamber.
One thing I noticed about the power valve is that you need to be careful about the large round mounting gasket thickness. I got one in a rebuild kit one time that had the gasket so thick that the bottom of the power valve hit the floor of that little chamber in the valve body so that when you mated the main body to the valve body, there was a little gap between them, so I had to find a thinner gasket for the power valve.

[Ford coupe]

Dave I think the carb you referred to is the Stromberg 97..I remember having my 36 carb apart to clean and the acc pump was in the middle of carb and the power valve was in the bottom of that pump hole or chamber I do believe..It was a Stromberg 97...Thanks much and happy motoring...