Can I use 6.5 (in stock locally) or should I really order a 7.5? Earlier you stated 6.5 is used by lowlanders for better gas mileage. Is 500-900ft lowland enough?

 

You should be fine with a 6.5. It will take a harder push on the gas to get enrichment, which probably isn't uncommon on a big heavy truck.

When you say it's available locally, is it the correct Model 94 type? There is a difference at the sealing surface. Later Model 2110 types are not flat all the way across the sealing surface, and don't generally seat all the way. They may be enough taller that the dome hits the throttle section and causes an air leak.

 

Good question! This is what I purchased: Holley Performance Products Single-Stage Power Valve 125-65 The picutre dosn't show the top from the correct angle, but I do remember that it has the tall window.

 

Either will work as long as you use the appropriate gasket. They each have there own specific gasket otherwise they will cause problems, so use the gasket that comes with the PV and not necessarily what is in a rebuild kit. At altitude your engine can not pull as much vacuum so at sea level (anything below 2000'), either would work.

Like Ross said a liitle more throttle blade to open the 6.5 PV. I am just assuming here that you just drive casually to cruises and the like and therefore probably would never open the PV, and if it was mine I would eliminate it entirely. Now if you are still responding code 3 to fire calls put a PV in there.

On another note your no start hot issue could be heat soak of your starter, either use a heat gun or touch the starter when you have a no start issue and see if the starter is hot. You may have to wrap it with one on the new hi-tech heat shield fabrics to help it stay cool.

 

Okay, so I have my carb quasi disassembled and have removed the existing power valve. I did a crude vaccume test on it and on the new one. The new one retains the vaccume noticeably better, but the old one still operates, but the vaccume drains down fast. I tried to install the new one, but it didn't seem to fit! I believe my carb is a ford script holley 94. Just like posted earlier, the old valve has the small top and many round holes. My new valve has the flat top and one big window. It seems as if I can't get the flat top to go in far enough. Anything I'm missing? Am I being stupid? I'm getting frustrated!!!!

 

Did you do what Ross or someone suggested earlier in the thread? Set the carb on the bench, fill with gas and see if it is leaking. Unless the power valve is leaking, forget about it, not your problem. JMHO.

 

I perfoemed a vaccume test on the old and new and the new one is much better at retaining a vaccum. The old one seems to leak, but it dosn't gush.

 

Remember, when installed, the PV diaphragm has fuel at some small positive pressure on one side, and manifold vacuum on the other. It can suck a lot of fuel thru even a small crack.

A bad PV will make it run rich all the time, not just dump gas when parked.

 

Some years ago I had bought a kit to rebuild my Ford carb on my 50 F-3. I still had the leftover parts to the kit. Yesterday, i put the new leftover power valve from that kit in my carb. It looks a bit different than the one I had used. The power valve I took out had a slow leak in the diaphram.

That really fixed it. I had it out yesterday and today. It has never started so good especially when hot. Wish I had taken a picture of the valve I used but I didn't know if it was going to be right or not.
Be sure to use a gasket under it. My old kit is a WELLS with a CK123A sticker on it and also 8BA-9590 sticker with a bar code and Oct 94 date. The instructions is for Holley Carb model -AA-1 and Model - 2100 DD, 2100. It must be for a Ford carb too. I don't know where I bought it. Hope this helps some. Patrick

 

I returned the Holley 125-65 as the spring retainer did not fit. I ended up finding what looks to be the proper power valve in a gp sorensen carb rebuild kit 96-478. That will be my project tomorrow afternoon. I'll let you all know how it goes!

 

You have to be careful with the kits that cover later Y-block carbs, because they include a Spark Control Valve that looks somewhat similar to a PV, but has a totally different function. Generally have a much larger dome. See below, these are all spark control valves. See how the brass plug is seated with no vacuum? A PV's plug will be up out of its seat with no vacuum.

 

Ross,
Thanks for the pictures and the info. I'll have to look to see just what I put in my carb. I may have put a spark control valve in it instead of a power valve. It runs fine with whatever I put in it yesterday. Patrick

 

The new power valve seems to be just the trick! Thanks for all your help! She did well on her drive today!

 

I had put in the spark control valve which lets no gas through when the vacuum drops. It didn't seem to have quite the power on the hills with full throttle. I now have a correct new power valve installed. Thanks for the help. I need all the power I can get on the big hills here. Patrick

 

Should make a huge difference!