I am familiar with the issues of differnt PV designs, so having a shoulder and some flat where the gasket goes, with some incompatability issues. I bought a Holley 94 rebuild kit from NAPA. I know they have right PV to fit my carb. My power valve is leaking through the throttle body into the intake manifold. If the truck sites for 48 hours or longer, it won't start due to all of the fuel draining out of the float bowl. I confirmed this by screwing the idle needles closed while the truck was idling and it still ran for a short time.

So here is a picture pf the PV that came in the NAPA kit. It has three numbers stamped on it (4, 8, and 5). So I am assuming the rating is 8.5. Does anyone know? I plan to put the new gasket on it with some Permatex "Aviation" gasket sealer. I am not replacing the flame arrester. Everything else on the carb seems OK.

Any tips for me?

 

No pic?

These are the diffferent styles of PV's. I'd be 99% sure the NAPA kit won't have the correct one. Their kits are really for the later 2110's which have the radiused shoulder.

Confused what you mean by "flame arrestor"? I don't know of any sealants that will last immersed in gas. Use one of the new teflon gaskets for a good seal.

 

Do you mean spark control valve when you say flame arrester? You may have the later 2110 carb. Please post a picture of the carburetor.

 

Here are two pictures of the carb. On the side it has "Ford 7RT". The PV that I got from NAPA looks just like the one on the left that Ross posted. No radiused edge, tall rectangular windows, Yes I meant spark control valve. I think it's purpose is to block backfire pressure from getting into the carb and damaging the diaphragm in the PV. Actually the gasket sealer I referenced is for gasoline, with and without ethanol.

So what's the concensus? Do I have the right PV for this carb? And what is the PV vacuum ratng?

 

Use with 7RT Carburetor:

AOAZ-9A565-A .. Economizer (Power) Valve / 0-5,000 ft. / Obsolete

MCDONALD OBSOLETE PARTS CO. in Rockport IN has 1 = 812-359-4965.

GREEN SALES CO. in Cincinnati OH has 7 = 800-543-4959.

MILLER OBSOLETE PARTS in Binghamton NY has 19 = 607-722-5371.
-------------------------------------------------------------------------------
A8TZ-9A565-A .. Economizer (Power) Valve / 5,000-10,000 ft. / Obsolete

NOS PARTS LTD in Waxahachie TX has 16 = 972-937-2201.

GREEN SALES CO. has 28.

 

Your carb is original/correct. We'd need to see a close up of the PV to tell if it's correct for the carb. Your carb should not have a spark control valve. Make sure you don't put the SCV where the PV should go!

These are various SCV's

 

Yes, my carb oes not use the SCV. It came in the rebuild kit, but is not used on my carb. Here are two pictures of the PV that I got from NAPA. The gasket was in the kit also. I thought about using a viton or ring, as I don't want this to leak. Someone mentioned a teflon gasket, but I don't know about where to get that. I really don't want the new PV to leak like the one I have.

Sorry I didn't attach the pic of the PV on my first post. I am still getting used to the process of attaching pictures. The rating of it appears to be 8.5 as marked. That might be a little high.

 

I finally got my front parking brake cable installed.

I wonder how many of you reading this have lifts in your shop? I sure would like to find a better and safer way to work.


How many of you have lifts in your shop? I finally got the front parking brake cable installed.

 

Yeah, it's hard to weld those leaky gas tanks with the truck sitting on the ground. He's being safe though, the right rear wheel is chocked.

The original PV is usually around 7.5 inches.
(I have 2x2 bbls. so I have 3.5s in mine)

The gasket you show is correct but I prefer the nylon:


Nylon Gasket (this might be what Ross meant by teflon, or there could be another type I've not seen)

Or the wider gasket found in this kit:

Basic Holley 94 rebuild kit

 

Actually I did a little research on how to choose PV ratings (according to Holley website). Measure vacuum with engine at idle (manual transmission in neutral). Then divide that by 2 to get the PV rating. My vcuum is about 20 inches of mercury. So a 10 would be optiml, but the 8.5 I have should be close enough. It doesn't open until about 3500 rpm, or lugging up a hill I guess when the carb vacuum drops below the PV rating. Right now mine is constantly leaking, running rich, and when I start it, it blows a big wad of black soot out of the tail pipe.
Once I get the carb off I can see whats going on but I am 100% convinced that the PV diaphragm is ruptured or gasket is leaking.

 

Vintage Speed sells a 9.5 and a 10.5. Actually, they sell everything from a 2.5 to a 10.5 in "X.5" increments.

If there is any chance you may change the PV later, there is a trick the flathead racers use. If you replace the bottom screw with a hex-head, you can remove the top 2/3 of the carb without having to remove the base. The other two screws are accessible from the top. It shouldn't dump fuel unless the PV is ruptured or leaking.

***Caution! If you do this, be careful you don't over tighten that bottom screw. The leverage of a wrench can produce torque more easily. You can warp the mating surface or strip the threads.***

 

The black "triangle" gasket usually results in leaks. Effie's got it, I meant nylon. Whatever you use, after it's tightened down, put the lower throttle section on without a gasket or screws, and make sure the dome of the PV isn't too tall, and holds the two sections apart.

Your PV looks to have some radius to it, but not as bad as some. 7.5 is the stock PV, usually way rich. I can't imagine a 10 in it, most people use a 6.5 or even a 5.5. The idle circuit controls mixture over a wide range, main jets only control (limit) WOT flow. #51 jets were stock.

 

Thankd Effie and Ross. That's a really good idea about replacing that upside down screw with a hex head one. Actually I can get the screw off by gripping it firmly on the head with my smaller slip joint pliers and gently backing it out. I know this because it was a little loose (leaking), and I tightened it slightly that way. It would ne great if I didn't have to remove that lower section of the carb.
That is a really good tip!

I could be wrong, but I think that triangle shaped gasket in the rebuild kit is meant for the spark control valve. It is not quite right for the PV, so I can see how it might leak.

My PV might be a 5.8, not 8.5 the way the markings looks. Once I get it open I will take a picture and post it with the existing PV in there. As for the nylon gasket / washer, I may be able to find one that's thin enough not to cause clearance issues. If I need to order a PV with a different rating I will do that. I have found that Tru Value hardware has small parts that none of the big bioxers keep in stock. It's amazing what I find there.

Today I am taking the truck to a tranmission shop to investigate a small gear oil leak that I think is coming from the rear seal. Depending on the cost to pull the seal and replace it, I may try some stop leak (ATP-205). It is not a large leak, just annoying.

 

So today I got the carb off. Here are some pictures I took imediately after getting the crb off. The reason for my problems was that there was no gasket at all under the powervalve. I unscrewed it on teh bench and took the picture. Note the picture of the throttle body, showing the fuel filled chanber under the PV. There was very little fuel left in the float bowl.




So I thnk that explains all of my symptoms:

Wouldn't start at all without long cranking if it had sat for over 24 hours (float bowl empty).
Blowing black soot out when it did start (massively rich from the fuel leakage under the PV).
Generally rich even after warmed up, and poor fuel economy. First start after the carb was put back (with the new PV and a gasket this time) I had to shoot some ether into the carb. I really hate doing that becasue I think it's rough on the engine.

Also Note the picture of the screws from the front of the carb. The one under the float bowl in front, I replaced with the black Allen Head screw. I decided not to iuse the gold colored hex head machine screw because of overtorque concerns, and it looks ugly under there.. I can get an allen wrench in there pretty easily. Thans Effie for that suggestion. It made it easier and the whole job took about one hour to do.

The screws are 1/4-28 (fine thread). Had to go buy those at the local Tru Value store.


Ended up using the on on the right to make future disassembly easier. The one on the left is what was in there. ANother good idea by Ford.





Full to the brim with fuel.





NO FRIGGING PV GASKET AT ALL!

JOE W

 

I'm glad it fixed the problem.

It's amazing how aggravating something simple can be.

I drove around with black tail pipes and spark plugs for about 4-5 years before I happened across a guy at Bristol that was racing a Flathead. I was in my mid 20's at the time and he was amazed someone my age even knew what a Flathead was. (I looked younger than I was) He's the one that told me about needing the different power valves and the bottom screw trick. I told him I had no idea where to find the different power valves. He opened a very organized tackle box that probably had 50 in various sizes and handed me two 4.5's. He was a great guy and I keep kicking myself for not remembering his name.