Power valve

[texas69bee]

I have the slightest hesitation(lean) from idle to wot. I’ve been working with the opening of the secondaries and I believe it’s where it needs to be as well as jet size and pump nozzle size.I have 14hg of vac, which tells me I need a #7 power valve. Some would say subtract 1.5hg then divide that by 2. That would give me a #6.

So here is my question...
If I want the power valve to open sooner, do you go up in size or down?
I am thinking up in size cause at idle I am at 14hg and the system has to go from 14hg and work it’s way down.

 

[vintage chromoly]

Up in inches opens sooner.

 

[69 GTX]

You can also change the accelerater cam & even install a 50cc pump. If itsi a Holley. Also make sure your timing is correct

 

[texas69bee]

Up in inches opens sooner.

So my thinking was correct. Go from a 6 to 7

 

[texas69bee]

You can also change the accelerater cam & even install a 50cc pump. If itsi a Holley. Also make sure your timing is correct

It’s a QuickFuel. Right now I’ve been working with the pink cam that it came with but have the others on hand.

 

[65-440]

14" at idle ? You do not want your power valve to match idle vacuum ! .... drive with a vacuum gauge and see what the reading is when the stumble occurs. My dart idles with 13" vacuum, I'm running a 9.5" power valve.

 

[hunt2elk]

It’s a QuickFuel. Right now I’ve been working with the pink cam that it came with but have the others on hand.

I got much better results on my cars by swapping out the pink cams. Whites and reds worked better for my motors. As far as power valves, the number on them is where the vacuum has to get down to before they open. So if you go to a higher number, it will open quicker. You need to run a hose into the cabin and drive around with a gauge hooked up. I'm certain with your idle reading you will be able to use a higher number valve. You want 2-3 inches less than wherever is the lowest reading during normal driving is.

 

[vance.dykes]

when the car is in drive what is your vacuum ? that is the number you cut in hafe . holly gives you the way to set and auj the accelerator pump lever bolt and lever

 

[texas69bee]

when the car is in drive what is your vacuum ? that is the number you cut in hafe . holly gives you the way to set and auj the accelerator pump lever bolt and lever

4 speed, so in neutral it’s at 14hg. When on the highway at a steady Speed, 21 hg

 

[hunt2elk]

4 speed, so in neutral it’s at 14hg. When on the highway at a steady Speed, 21 hg

What does it do when taking off and going through the gears normal driving? I bet you could put in a 10.5 valve with no issues.

 

[texas69bee]

What does it do when taking off and going through the gears normal driving? I bet you could put in a 10.5 valve with no issues.

Right now.. I put in a 8.5 power valve, still have the pink cam in. Hesitation is gone but running fat at wot. Getting 11 for AF ratio. AF at idle=14.5 steady cruise=14.2 secondary open=13.5

 

[65-440]

Looks like it's time for some jet changes !

 

[texas69bee]

Looks like it's time for some jet changes !

I was thinking about a pump nozzle change. All other areas seem to be fine except at wot. There is a .031 in it right now but the next smaller size is a .028.

 

[hunt2elk]

Squirters wont change your wot a/f. Try a couple size smaller secondary jets and see what happens.

 

[65-440]

Squirters wont change your wot a/f. Try a couple size smaller secondary jets and see what happens.

Bingo.. I would say go down 2 sizes and see how it changes

 

[texas69bee]

Squirters wont change your wot a/f. Try a couple size smaller secondary jets and see what happens.

Would a cam change, change AF at wot?

 

[65-440]

Would a cam change, change AF at wot?

Accelerator pump cam ? No, not at all. That only affects the duration and amount of initial pump shot. Important yes but no affect during WOT ..

 

[texas69bee]

Accelerator pump cam ? No, not at all. That only affects the duration and amount of initial pump shot. Important yes but no affect during WOT ..

Here is an article that supports what you and hunt2elk are saying. I’ll make the changes and report back but much needed rain is in the forecast.
https://innovatemotorsports.com/resources/carb-tuning-hero.php

Thanks guys!!!