The Ford Barn

D. Jones · 11-07-2013, 12:21 PM

My 59ab has been running real rich, lots of soft soot on the plugs, I went from 51 main jets to 49's and it is still too rich, but somewhat better than before. Elevation here is 3600'. The float bowl has always leaked down after a few days requiring some cranking to get started. When I rebuilt the Holly 94 I put in the new power valve that came with the kit and I suspect that is the cause of the leak down. Today I pulled the carburetor and looked at the power valve and didn't see anything that I thought indicated the vacuum fall needed to open. I took another older power valve from another 94 and put that in to see if that solves the leak down. I'm hoping that it may also help with the too rich problem. I didn't see anything that indicated the vacuum point on it either.

So how do I tell the vacuum rating of a power valve?

Charlie ny · 11-07-2013, 02:34 PM

D.
Some PV's are marked some are not. The genuine Holley PV's are marked on the
metal face that surrounds/protects the diaphragm. Others are stamped on the brass
nose that extends into the bowl. Remember these PV's come from various sources
and again some have no markings at all.
Most PV's are supplied as die castings and the gasket faces are usually not
exactly square or concentric or flat to the thread. I prefer to machine the gasket
face of the PV to guarantee flatness concentricity and squareness to the threads.
I recently machined a bunch of PV's and found them to be as much as .015
off....as cast they would NEVER seal......I will descend from the podium.
Oh yeah I make my own PV gaskets too.
Charlie ny

D. Jones · 11-07-2013, 04:21 PM

Charlie ny.

Thanks for your reply.

If I may ask, when you machine the gasket face do you just clean it up to "flat and in plane", or are you taking it down further to the radius? How are you holding the valve to machine it? I'm assuming you made a fixture to hold it by the threaded end in a lathe chuck leaving enough room to get to the gasket surface.

As you have most likely surmised I'm trying to get the main jets and power valve balanced to the needs of the motor at the altitude where I live, 3600'. I've not seen any kind of standard reference regarding altitude, so I'm in to trying different combinations to try and get it right.

ken ct · 11-07-2013, 06:01 PM

Charlie modifies all my PV I get from 1 of my suppliers, I have 2 suppliers. I use strictly 5.5 which open a lot slower than run of the mill 7.5 ones. Charlie has them too. Mine are marked on the brass knob end. ken ct. 5.5 seem to work in combo with .049 MJ's. 3600 elevation is not high enough for a jet change, Usually change starts @ 5000. Hope we helped you. Keep us posted. ken ct.

Charlie ny · 11-07-2013, 08:42 PM

D,
I'm fortunate to have an extremely accurate lathe. When I machine PV's I use
a .500 dia collet in the head stock. I very gingerly grip the PV by the threads and
use a diamond parting tool to face the gasket surface to a cleanup. I machine the
face down to .560 diam. This leaves a register diam. for the gasket to radially locate
on. I make my own gaskets from a killer plastic material called DELRIN. The gasket
is .045 thick .750 outside diam and you guessed it .560 inside diameter which nicely
locates on the register diam of the PV.
I like 5.5"hg PV's as does Ken. At sea level I like 50 or 51 jets.
94's demand zero vacuum leaks. A loose throttle shaft or a warped bowl
will bite ya everytime.
Charlie ny

D. Jones · 11-07-2013, 09:59 PM

Sponsored Links (Register now to hide all advertisements)

Charlie ny,

I too have a reasonably accurate lathe and a collet chuck for it. I'm always reluctant to grip threads to hold a part to machine the part, but may just try it. I like the Delrin idea, I've used it for some projects. I can make up a punch and die to make the gasket if needed. A vacuum check by gauge doesn't seem to indicate any leaks, but I'll give the carb another going over if things don't improve. I'm going to run the 49's and the old power valve for a while to see if the soot goes away. If it doesn't then I'll take another carb and go through it making sure every surface is flat and tight and the throttle shaft doesn't leak and I'll pick up a 5.5 power valve as I don't see any marks on the ones I have.

Thanks for the help/information.

D. Jones · 11-08-2013, 07:58 PM

Update:

Today I made a 60 mile round trip at highway speed, 55 MPH, when the truck cooled off I pulled a couple of the plugs and they are much cleaner, no more fluffy soot, and are starting to look like I think they should. The truck ran well and seemed to accelerate a little better. I'll run it as is for a while around town and keep checking them to make sure it's not too lean.

Tomorrow I'm going to look for a Holly 5.5 power valve as I still don't know what I have in the carburetor.

Thanks for the input.

11-07-2013, 12:21 PM	#1
D. Jones Senior Member Join Date: Jan 2013 Location: Bend, Oregon Posts: 514	Are power valves marked My 59ab has been running real rich, lots of soft soot on the plugs, I went from 51 main jets to 49's and it is still too rich, but somewhat better than before. Elevation here is 3600'. The float bowl has always leaked down after a few days requiring some cranking to get started. When I rebuilt the Holly 94 I put in the new power valve that came with the kit and I suspect that is the cause of the leak down. Today I pulled the carburetor and looked at the power valve and didn't see anything that I thought indicated the vacuum fall needed to open. I took another older power valve from another 94 and put that in to see if that solves the leak down. I'm hoping that it may also help with the too rich problem. I didn't see anything that indicated the vacuum point on it either. So how do I tell the vacuum rating of a power valve?

11-07-2013, 02:34 PM	#2
Charlie ny BANNED Join Date: May 2010 Posts: 3,019	Re: Are power valves marked D. Some PV's are marked some are not. The genuine Holley PV's are marked on the metal face that surrounds/protects the diaphragm. Others are stamped on the brass nose that extends into the bowl. Remember these PV's come from various sources and again some have no markings at all. Most PV's are supplied as die castings and the gasket faces are usually not exactly square or concentric or flat to the thread. I prefer to machine the gasket face of the PV to guarantee flatness concentricity and squareness to the threads. I recently machined a bunch of PV's and found them to be as much as .015 off....as cast they would NEVER seal......I will descend from the podium. Oh yeah I make my own PV gaskets too. Charlie ny

11-07-2013, 04:21 PM	#3
D. Jones Senior Member Join Date: Jan 2013 Location: Bend, Oregon Posts: 514	Re: Are power valves marked Charlie ny. Thanks for your reply. If I may ask, when you machine the gasket face do you just clean it up to "flat and in plane", or are you taking it down further to the radius? How are you holding the valve to machine it? I'm assuming you made a fixture to hold it by the threaded end in a lathe chuck leaving enough room to get to the gasket surface. As you have most likely surmised I'm trying to get the main jets and power valve balanced to the needs of the motor at the altitude where I live, 3600'. I've not seen any kind of standard reference regarding altitude, so I'm in to trying different combinations to try and get it right.

11-07-2013, 06:01 PM	#4
ken ct BANNED Join Date: May 2010 Location: stratford,ct Posts: 5,971	Re: Are power valves marked Charlie modifies all my PV I get from 1 of my suppliers, I have 2 suppliers. I use strictly 5.5 which open a lot slower than run of the mill 7.5 ones. Charlie has them too. Mine are marked on the brass knob end. ken ct. 5.5 seem to work in combo with .049 MJ's. 3600 elevation is not high enough for a jet change, Usually change starts @ 5000. Hope we helped you. Keep us posted. ken ct.

11-07-2013, 08:42 PM	#5
Charlie ny BANNED Join Date: May 2010 Posts: 3,019	Re: Are power valves marked D, I'm fortunate to have an extremely accurate lathe. When I machine PV's I use a .500 dia collet in the head stock. I very gingerly grip the PV by the threads and use a diamond parting tool to face the gasket surface to a cleanup. I machine the face down to .560 diam. This leaves a register diam. for the gasket to radially locate on. I make my own gaskets from a killer plastic material called DELRIN. The gasket is .045 thick .750 outside diam and you guessed it .560 inside diameter which nicely locates on the register diam of the PV. I like 5.5"hg PV's as does Ken. At sea level I like 50 or 51 jets. 94's demand zero vacuum leaks. A loose throttle shaft or a warped bowl will bite ya everytime. Charlie ny

11-07-2013, 09:59 PM	#6
D. Jones Senior Member Join Date: Jan 2013 Location: Bend, Oregon Posts: 514	Re: Are power valves marked Sponsored Links (Register now to hide all advertisements) Charlie ny, I too have a reasonably accurate lathe and a collet chuck for it. I'm always reluctant to grip threads to hold a part to machine the part, but may just try it. I like the Delrin idea, I've used it for some projects. I can make up a punch and die to make the gasket if needed. A vacuum check by gauge doesn't seem to indicate any leaks, but I'll give the carb another going over if things don't improve. I'm going to run the 49's and the old power valve for a while to see if the soot goes away. If it doesn't then I'll take another carb and go through it making sure every surface is flat and tight and the throttle shaft doesn't leak and I'll pick up a 5.5 power valve as I don't see any marks on the ones I have. Thanks for the help/information.

11-08-2013, 07:58 PM	#7
D. Jones Senior Member Join Date: Jan 2013 Location: Bend, Oregon Posts: 514	Re: Are power valves marked Update: Today I made a 60 mile round trip at highway speed, 55 MPH, when the truck cooled off I pulled a couple of the plugs and they are much cleaner, no more fluffy soot, and are starting to look like I think they should. The truck ran well and seemed to accelerate a little better. I'll run it as is for a while around town and keep checking them to make sure it's not too lean. Tomorrow I'm going to look for a Holly 5.5 power valve as I still don't know what I have in the carburetor. Thanks for the input.