Just a quick note about a quick fix. My 1950 F1 flathead V8 started running rich and had a roll to the idle. I had to up the idle speed to keep it running and the idle jets had no effect.

I was getting ready to tear into the carb, (which was rebuilt by the PO less than 2 years ago) but asked a long time Ford man to listen to it. In about 10 seconds he said change the power valve. In another minute or so he explained how easy it was to change and that I should buy the power valve at NAPA because they had the right parts at a good price. I stopped at NAPA on Monday, they did not look at me funny asking for a part for a 60 year old truck, just punched the numbers into their computer and said they would have it first thing in the morning. Picked it up this morning, ten dollars and change. Took all of about 5 minutes to put it in the carb after getting the carb off. Runs like new again. Took a nice 25+ mile drive this evening.

The power valve increases the fuel at low vacuum. The PV has a diaphragm that can get pin holes in them, thus running rich. In my case the PV was finger tight and was a slightly different style with a hard fiber washer. I think it either wasn't the right PV or improperly installed. The NAPA PV has a soft gasket and it looks like the one in the manual.

This may be old hat for most of you but this was my first time in a Holly/Ford 94.

 

PV's are the weak point in 94's, for sure. I'd be cautious about the PV's NAPA has tho; the old style our trucks came with had a straight shank while the newer ones are kind of flared where the stem meets the flat. The sealing surface is also a little different. This makes them hard to seal without leakage. Vintage Speed and some others offer modern ones that have been machined to the original profile.

 

I buy viton o-rings from McMaster Carr, work on any type of power valve surface. But with M-C, you have to buy them in bulk $12 for 25. By the way, turning in the idle screws whilst engine is running is a way to test for bad pv. If it keeps on idling with idle screws in, the pv is out. If it dies, the pv is fine.

 

Just to help clarify the part you're talking about. I'm assuming it's part #9A565 & #9A588:



I don't see a corresponding apart for the 6 cylinder carb. This is a poor drawing of the 6 cylinder from the parts catalog. First the throat is incorrect. The truck throat isn't straight in the truck, the truck throat is flared out in the center <==> to accommodate the clamp on the air cleaner. It is also missing the nozzle bar like the one pictured with the V8 carb. This is the same carb they show in the car parts catalog. Anyone have the drawing for the truck?:

 

That is correct.

I had read about the problem with some of the new PV's so was looking for the differences. If I understood the description of the difference it looked like the one that I pulled out may have been the new/wrong style and the NAPA was correct. The NAPA, I was happy to see, was also marked as made in the USA.

 

That's good to know, thanks! I am playing with non-standard PV's, as I am at 5300 ft altitude. I've just received a 6.5 PV, one inch less than stock, which should compensate for the altitude.

BTW, interesting article on a NEW trend on Made in USA!

Backshoring Gains Momentum as More U.S. Companies Bring Production Home | Machine Design

 

Actually a 5.5 pv works well at our altitudes. Kind of funny, a very large (respectable) carb rebuilder and kit company refused to put a 5.5 pv in a kit for me instead of the regular 7.5, said it would cause a "lean" condition and "burn up the engine". Yet, some very respectable independent builders use this pv all the time and get rave reviews, no toasted engines! I've used them myself and have had customers tell me their mileage picked up and... no problems.

Keep in mind, the pvs aren't accurate in the least as to their advertised rating.

 

The power valve in the six cylinder carb of that vintage is mechanical, not a vacuum operated diaphragm. It is part number 9594 and is actuated by a piston. The nozzle bar is different on the six cylinder carb because it changed into a "high discharge" nozzle in 1952 for the AA1 (94). The six cylinder carb as pictured was no longer used in 1952 with the new OHV six. The famed glass bowl 1904 Holley was the man of the hour at this point.

The parts drawings in some of those parts catalogs are of the same accuracy as the instructions in kits that cover the AA1s from inception in 1938 to the demise in 1956. Too many different carbs being compiled together.

 

Interesting; this 5.5 works well in single carb applications? It does seem like it would be lean. I ordered a 5.5 and a 6.5, I'll have to try.

 

Yes, it seems to work well. A fellow I communicate with who builds and tests each carb (EFV8 member and vendor) says the Carquest pvs he uses test anywhere from 4.0-5.5. As you know, most AA1s had 51 jets from new, but some rebuilders of good repute use 49-50 jets with the 5.5 pv.

 

all i will say is da-- junk pos holley's !!!!!!!!!!!!! all of them with a power valve are tempermental pain in the posteriors !!!!!!!!! the 52 just ate it's pv , so the rebuilt 94 on it has to came apart , and i'm still gonna put the { gasp !!!!!!!!! } rochester 2 jet on mine w/ no. 41 jets instead of dealing with them holley's any more than i have too !!!!!!!!!!!!! used to have nothing but good luck with them , especially in racing then it all went sideways and now taking a hammer to them seems like the right thing too do !!!!!!!!!!!!!!!!!!!