The Ford Barn

bullrunmotor · 05-09-2020, 11:00 PM

My 59A pulls good and strong-doesn't miss-but sometimes feel like it's surging around 35-40. My ignition is A-OK. Sometimes floods easily after turning it off and coming back when still warm, Plugs aren't sooty. Don't really know what it would run like if the power valve was shot. Thanks in advance

Tinker · 05-09-2020, 11:09 PM

When it surges pull the choke a little. Should show it's running lean if it gets better. 35-40 what end of gearing you in. 2nd high rpm or 3rd lug. Just a thought.

flatheadmurre · 05-10-2020, 02:36 AM

Powervalves fail in mainly 2 ways...they either break in the diaphragm leaking...or they get stiff from age.
Leaking shows in the way you say flooding when shut of...lift the top of carburetor to check if floatbowl is empty after sitting a while then it´s leaking.
If they get stiff it´s trickier cause they work but behave like the jetting is off...get powervalve out and if it doesn´t move nice and smooth pushing by hand time for a new for sure.

philipswanson · 05-10-2020, 10:39 AM

They can also leak or bypass at the gasket surface which is fairly common, especially with that carburetor.

BUBBAS IGNITION · 05-10-2020, 11:29 AM

Quote:

Originally Posted by flatheadmurre

Powervalves fail in mainly 2 ways...they either break in the diaphragm leaking...or they get stiff from age.
Leaking shows in the way you say flooding when shut of...lift the top of carburetor to check if floatbowl is empty after sitting a while then it´s leaking.
If they get stiff it´s trickier cause they work but behave like the jetting is off...get powervalve out and if it doesn´t move nice and smooth pushing by hand time for a new for sure.

OR ya got the wrong valve for the car and engine. Power valve adds fuel when needed based on load ex: a 7.5 valve would add additional fuel when the engine vac went to 7.5 or below . A change in gearing , tuning etc might either NOT allow the engine to reach 7.5 when it needed the fuel OR going the other way vac is below the 7.5 level most of the time . Everyone needs to spend a weekend with some new different power valves and a vac gauge , Could be very rewarding ????

JayChicago · 05-10-2020, 12:05 PM

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Quote:

Originally Posted by BUBBAS IGNITION

Everyone needs to spend a weekend with some new different power valves and a vac gauge , Could be very rewarding ????

Do you mean driving with the vacuum gauge in the cockpit so you see what it’s doing under real driving conditions?

tubman · 05-10-2020, 01:39 PM

Bubba's right. I had a problem with my Corvette, so I hooked up my vacuum gauge and taped it to the windshield wiper and spent a full morning running around, It WAS very informative. The engine had an aftermarket cam and as I result, I changed to a different power valve, which resulted in improved driveability.(The Corvette had a front opening hood, so leaving it ajar to run the hose to the gauge was not a problem.)

JayChicago · 05-10-2020, 03:27 PM

Good. Thanks, tubman. Just wanted to confirm what I was planning to do with my new '37. It has a big cam, terrible performance at low RPM, new plugs turn black in under 100 miles . Thought I would start the tuning process by seeing where vacuum is going under acceleration. (5.5 power valve in it now) But I also have no clue yet how the distributor was set up, so I'm worried this tuning process may quickly get too confusing for this novice. I'll probably be asking a lot of questions when I get into it.

Mart · 05-10-2020, 06:00 PM

There are lots of reasons a 94 will run rich.

google the following:

94 running rich site:www.fordbarn.com

Lots of threads there.

In this one I list out the things I have personally experienced:

https://www.fordbarn.com/forum/showthread.php?t=197943

Mart.

flatjack9 · 05-10-2020, 08:16 PM

If you are running a big cam, it is important to have more advance at the lower engine rpm. The cam will tend to dilute the intake charge at lower revs and it will burn slower, so you need more advance. What is your cam and what power valve do you have?

tubman · 05-10-2020, 08:45 PM

"Flatjack9" - I always like to get all of the information about something when I can. As I stated in another thread here, I like to use a vacuum gauge to set the timing in a modified engine, since the factory specifications probably no longer apply.

Do you think that this method will a produce the extra advance you are referencing?

flatjack9 · 05-11-2020, 08:06 AM

I would think so. Then you have to be concerned about the total advance. I install a timing pointer on all the engines I build.

Charlie ny · 05-11-2020, 10:50 AM

The pointer issue is so critical in modified early motors. The use of an air/fuel gauge is
just as critical. Most a/f meters come with a weld in bung that locates a foot or so back

in the exh pipe. I hay wire the meter into the cab and a buddy records data as I drive.
It is a poor mans dyno but it works. It would take some far out guess work and seat of the pants to beat an O2 sensor delivering infio inside the pipe
Charlie ny

05-09-2020, 11:00 PM	#1
bullrunmotor Senior Member Join Date: May 2010 Location: Virginia Posts: 210	What are the symptoms of a bad power valve in a 94 model carburetor? My 59A pulls good and strong-doesn't miss-but sometimes feel like it's surging around 35-40. My ignition is A-OK. Sometimes floods easily after turning it off and coming back when still warm, Plugs aren't sooty. Don't really know what it would run like if the power valve was shot. Thanks in advance

05-09-2020, 11:09 PM	#2
Tinker Senior Member Join Date: May 2010 Location: MN Posts: 7,053	Re: What are the symptoms of a bad power valve in a 94 model carburetor? When it surges pull the choke a little. Should show it's running lean if it gets better. 35-40 what end of gearing you in. 2nd high rpm or 3rd lug. Just a thought.

05-10-2020, 02:36 AM	#3
flatheadmurre Senior Member Join Date: Apr 2015 Location: Sweden Posts: 3,045	Re: What are the symptoms of a bad power valve in a 94 model carburetor? Powervalves fail in mainly 2 ways...they either break in the diaphragm leaking...or they get stiff from age. Leaking shows in the way you say flooding when shut of...lift the top of carburetor to check if floatbowl is empty after sitting a while then it´s leaking. If they get stiff it´s trickier cause they work but behave like the jetting is off...get powervalve out and if it doesn´t move nice and smooth pushing by hand time for a new for sure.

05-10-2020, 10:39 AM	#4
philipswanson Senior Member Join Date: Oct 2015 Location: Bonita, CA Posts: 1,374	Re: What are the symptoms of a bad power valve in a 94 model carburetor? They can also leak or bypass at the gasket surface which is fairly common, especially with that carburetor.

05-10-2020, 01:39 PM	#7
tubman Senior Member Join Date: Dec 2013 Location: Minnesota, Florida Keys Posts: 10,303	Re: What are the symptoms of a bad power valve in a 94 model carburetor? Bubba's right. I had a problem with my Corvette, so I hooked up my vacuum gauge and taped it to the windshield wiper and spent a full morning running around, It WAS very informative. The engine had an aftermarket cam and as I result, I changed to a different power valve, which resulted in improved driveability.(The Corvette had a front opening hood, so leaving it ajar to run the hose to the gauge was not a problem.)

05-10-2020, 03:27 PM	#8
JayChicago Senior Member Join Date: Jan 2019 Location: Chicago Posts: 728	Re: What are the symptoms of a bad power valve in a 94 model carburetor? Good. Thanks, tubman. Just wanted to confirm what I was planning to do with my new '37. It has a big cam, terrible performance at low RPM, new plugs turn black in under 100 miles . Thought I would start the tuning process by seeing where vacuum is going under acceleration. (5.5 power valve in it now) But I also have no clue yet how the distributor was set up, so I'm worried this tuning process may quickly get too confusing for this novice. I'll probably be asking a lot of questions when I get into it. Last edited by JayChicago; 05-10-2020 at 03:41 PM.

05-10-2020, 06:00 PM	#9
Mart Senior Member Join Date: May 2010 Location: Solihull, England. Posts: 8,744	Re: What are the symptoms of a bad power valve in a 94 model carburetor? There are lots of reasons a 94 will run rich. google the following: 94 running rich site:www.fordbarn.com Lots of threads there. In this one I list out the things I have personally experienced: https://www.fordbarn.com/forum/showthread.php?t=197943 Mart.

05-10-2020, 08:16 PM	#10
flatjack9 Senior Member Join Date: May 2010 Location: Oshkosh, Wi Posts: 4,526	Re: What are the symptoms of a bad power valve in a 94 model carburetor? If you are running a big cam, it is important to have more advance at the lower engine rpm. The cam will tend to dilute the intake charge at lower revs and it will burn slower, so you need more advance. What is your cam and what power valve do you have?

05-10-2020, 08:45 PM	#11
tubman Senior Member Join Date: Dec 2013 Location: Minnesota, Florida Keys Posts: 10,303	Re: What are the symptoms of a bad power valve in a 94 model carburetor? "Flatjack9" - I always like to get all of the information about something when I can. As I stated in another thread here, I like to use a vacuum gauge to set the timing in a modified engine, since the factory specifications probably no longer apply. Do you think that this method will a produce the extra advance you are referencing?

05-11-2020, 08:06 AM	#12
flatjack9 Senior Member Join Date: May 2010 Location: Oshkosh, Wi Posts: 4,526	Re: What are the symptoms of a bad power valve in a 94 model carburetor? I would think so. Then you have to be concerned about the total advance. I install a timing pointer on all the engines I build.

05-11-2020, 10:50 AM	#13
Charlie ny BANNED Join Date: May 2010 Posts: 3,019	Re: What are the symptoms of a bad power valve in a 94 model carburetor? The pointer issue is so critical in modified early motors. The use of an air/fuel gauge is just as critical. Most a/f meters come with a weld in bung that locates a foot or so back in the exh pipe. I hay wire the meter into the cab and a buddy records data as I drive. It is a poor mans dyno but it works. It would take some far out guess work and seat of the pants to beat an O2 sensor delivering infio inside the pipe Charlie ny