What power valve number for 21" hg

[HOWDY69]

My new Holley 4150 (80783C) came with a 6.5 power valve. I am pulling 21" Hg at 900 RPM idle. Any idea what would be a good power valve. I have read using idle vacuum divided by 2 or idle vacuum minus 2 but I think these formulas are for engines with much lower vacuum.

4700 pound F250, 410FE, CJ valves and mild porting, RPM intake, stock exhaust manifolds with dual oem pipes/muffler, Mellings MTF-4 torque cam.

[Dragon]

It is for any Holley no matter what the vacuum. The heavier the vehicle the more times in a day the vacuum will drop low. A 6.5 is good. Now if you want to do daily driving and get better mileage get a 2 stage power Valve the 125-207. I just ordered one.

125-207 Two–Stage Power Valve For Model 4160 1st Stage Opening 10.5" Hg 2nd Stage Opening 5" Hg.
I recommended the 125-207 because of your high vacuum.
Models 4150, 4160,
1. Two-stage power valve should not be used in any vehicle which sees occasional drag strip use, or in any carburetors with power valve channel restrictions greater than .060” (this includes the 3310 and the conventional double pumper line which require high capacity power valves). Excessive leanness could result from the limited flow capacity of the two-stage valve.
2. The 125-206 or 125-208 is recommended for most applications, while the 125-207 is recommended for vehicles which will see frequent high altitude use (above 4000 ft.).
Power Valve Specifications
Part Number 1st Stage Opening 2nd Stage Opening 1st Stage Restriction
125-206 Model 4160-4150 12.5” Hg 5.5” Hg .028”
125-207 Model 4160-4150 10.5” Hg 5” Hg .021”
125-208 Model 4160-4150 10.5” Hg 5.5” Hg .028”
When the two-stage power valve is applied with these guidelines in mind, fuel economy and driveability improvements will often be realized and exhaust emissions will be unaffected.

On a note about your cam read through this whole thing. Ford Trucks Forum

[HOWDY69]

Wow…that is great information. My commute is 10 miles each way and I usually stay on surface streets because the freeway gets backed up. So there is a lot of stop and go. I had the 6.5 for three years and didn’t notice a particular problem. It was just when I started learning to tune the carb that the question about the power valve came up. A tuning guide said to get the right power valve before changing jets since they work in combination.

What is the issue with using a two stage power valve at the track?

[Dragon]

It does not flow enough fuel for anything but drag racing where the motor sits at peak all the way. On tracks where you cycle the throttle up and down It would not feed enough fuel at the low range only at the high range. So 10.5 is restricted fuel flow and 5 is standard power valve opening.

[Ranchero50]

The power valve purpose is to put more fuel in the engine under load, thus 'power' valve, it uses the engines manifold vacuum signal to determine when to add more fuel. You can change the point when you want it to add more fuel by specing a different vacuum point.

I would suggest just putting it back together stock and taping a vacuum gauge to the windshield for a couple days so you get real world vacuum readings. The 6.5" spec is when the power valve opens to put more fuel into the circuit. So if your engine is pulling above 6.5" of vacuum it's running on the main jets (and idle circuit).

Any suggestions are moot until you know your driving style by the guage and seat of the pants feel of the acceleration curve.

My best advice is to go buy a copy of Mike Urich's Holley Carburetor Handbook from HP books and read it up. Most of your questions and concerns would be self answered by reading it.

Jamie

[71cc]

The power valve purpose is to put more fuel in the engine under load, thus 'power' valve, it uses the engines manifold vacuum signal to determine when to add more fuel. You can change the point when you want it to add more fuel by specing a different vacuum point.

I would suggest just putting it back together stock and taping a vacuum gauge to the windshield for a couple days so you get real world vacuum readings. The 6.5" spec is when the power valve opens to put more fuel into the circuit. So if your engine is pulling above 6.5" of vacuum it's running on the main jets (and idle circuit).

Any suggestions are moot until you know your driving style by the guage and seat of the pants feel of the acceleration curve.

My best advice is to go buy a copy of Mike Urich's Holley Carburetor Handbook from HP books and read it up. Most of your questions and concerns would be self answered by reading it.

Jamie

Good advice.. If you are jetted close to lean you will actually feel the power valve open. A single stage power valve flows the equivilant of 6 jet sizes. That is why it affects fuel economy. The ideal setup is to jet rich enough that you don't have to get so deep in the throttle to get your power.Overly rich actually hurst throttle response. You should be able to jet down 2-4 sizes safely. At about 6 jet sizes it will begin bucking at light throttle heavy load, and will have a surge of power at power valve opening. The two stage power valve helps bridge the gap from lean to rich by opening "gradually". Step down in jet sizes in steps of 2. It is a waste of time to go 72,71,70 etc.. Ambiant temp usually varies enough to prompt jet changes from summer to winter.

[HOWDY69]

First of all thanks for the help.
Ranchero50: I will definitely get and read the book and will put on a temporary vacuum gage.
Dragon: Thanks for the HolleyTV link it has been a big help.
71cc: Thanks for the additional explanation.

This is where I am. I installed a new carburetor yesterday and I have never tuned a carb before. I live at sea level and the temperature has been between 40 and 50 F. Here is what I have done in chronological order.

I bench adjusted the low idle screw to show about 0.020 of the slot. I adjusted the secondary throttle plate so the light gap was about the same. This adjustment required about ¼ turn of each screw to open the plates a little more than out of the box.

I replaced the stock jets (67/73) with the 69/75 set that was in my old carburetor. I removed the Ford Automatic parts from the old carburetor and put them on the new one.

I installed the carburetor, connected a vacuum gage to the base plate and connected a RPM meter.

When I started the engine it ran a little rough and the high idle did not work properly. I held the truck at high idle using the throttle until it warmed up. Once warm it idled a little rough.

I adjusted the primary mixture screws to achieve maximum vacuum and rpm. The screws ended up open 2 full turns. Low idle was 900 rpm at 21 in Hg and drive idle was 750 rpm. Idle was smooth.

I drove around the area for about 10 minutes and the truck ran OK. I pulled into the driveway, turned off the truck and immediately restarted the truck without any problem.

Today I went out to start the truck and it would turn over but would not start. I turned the primary metering screws in 1/8 of a turn (I can not remember where I read to do this because I have been reading from a lot of sources) and was able to get the truck to start. Again the electric choke did not set to high idle and I warmed the truck up by holding the throttle at high idle. The metering screws are now open 1 and 7/8.

I drove the truck around the block (about 1 mile) in first gear at 20 miles per hour which would be about 50ish in 3rd gear. This seemed like a good way to keep the rpm’s up but keep close to home. I pulled into the driveway and shut off the engine. I pulled two plugs and they read lean, they looked essentially new with white porcelain.

I am headed to get some vacuum line so I can install a gage.

[Dragon]

First of all thanks for the help.
Ranchero50: I will definitely get and read the book and will put on a temporary vacuum gage.
Dragon: Thanks for the HolleyTV link it has been a big help.
71cc: Thanks for the additional explanation.

I bench adjusted the low idle screw to show about 0.020 of the slot. I adjusted the secondary throttle plate so the light gap was about the same. This adjustment required about ¼ turn of each screw to open the plates a little more than out of the box.

You should have left the secondary idles screws alone. In over 120 Holleys I have played with, only my Dual 950 3 barrel setup required the secondary idle speed adjusted. That was because a 950 is a 4160 and I added the double pumper rear metering block to each carb as the carbs were mounted sideways. The secondary of 1 carb and the primary of the other carb were on the same side of the manifold. Each group of barrels rode right above the runners for each two cylinders on one side.

The front and rear idle speed adjustments are not supposed to be the same. The secondaries will not run the engine. The reason the plates are open is to allow a slight amount of airflow to start the fixed idle feed and transition circuits to bleed enough fuel so that when the secondaries do open the main wells are pre-filled with air fuel mix.

Every Holley I pulled from a box needed the idle mixture screws slightly adjusted whether at high altitude or sea level.
Every electric choke I have had needed the fast idle speed adjusted up. You need a 1/4 inch open end wrench.

[HOWDY69]

OK here are some initial vacuum results. I drove around the neighborhood and on a few surface streets up to about 50 mph. The engine temperature was 160 for all readings.

High idle 22.0
Low idle 19.5
In Drive 16.5

Mellow driving, mild acceleration 17 to 22
More typical acceleration 14 to 17
Goose-it 10ish
Kick down 4.5

I checked two spark plugs after returning home and spark plug porcelain was white.

Most of the driving was between 17 and 22 in Hg. My conclusion is primary jets are lean. Book says the spark plug should be tan or light brown. The power valve (6.5) only opened when I accelerated hard enough to kick-down into second. So I think I need to increase jet size even if I choose to go with a two stage power valve.

Does this make sense?

[Ranchero50]

check the floats before doing anything else and close the secondaries until just before they start sticking. Then readjust and retest.

Those two setting will change everything.

Also find a quiet industrial area and do a full throttle run, then cut the ignition before slowing down. Check the plugs. Lean driving isn't really bad and the color checks went out the window can be anything under the sun with the gas mixes now. They should have a little tan to them after the full throttle run. They will also be lighter with the good ignition.

How did it drive? Smooth acceleration? Idle decent?

The choke, loosen the cover screws and rotate the black cap so the choke will click to fast idle when cold and you open the throttle slightly.
Jamie

[Dragon]

Go up one jet size. 160 is not good for a street motor too low. Fuel will puddle in the intake runners leaning the engine even more. Even tunnel port and SOHC motors had 180s in them for racing from factory.