Power valve

[Bird 426]

What if I just eliminate the power valve on a Sixpack, anyone done that on the street?

 

[BSB67]

Why? What are you trying to accomplish?

 

[Canadian1968]

Probably not a good idea !

 

[steve340]

Better to keep it. You will have trouble calibrating either the cruise or WOT mixture. The PV is the way the carb jet size can be right for cruise and when the vacuum in the manifold drops the PV opens and the PVCR adds extra fuel so the carb is rich enough for WOT operation.
If you put bigger jets in to compensate for no PV it will be pig rich at cruise.
Smaller jets to get the cruise mixture right and you may get some lean cylinders at WOT.

 

[Bird 426]

Okay, you talked me out of it. It was a what if question. I have been battling a rich, lean issue for several years and just can not get a handle on it. So I was thinking of trying something else instead of expecting different results redoing the same damn thing over and over. The engine ran like a freight train when I first built it, I have done something or something has changed, but like the song, I'm trying.
Thanks for helping!

 

[451Mopar]

Okay, you talked me out of it. It was a what if question. I have been battling a rich, lean issue for several years and just can not get a handle on it. So I was thinking of trying something else instead of expecting different results redoing the same damn thing over and over. The engine ran like a freight train when I first built it, I have done something or something has changed, but like the song, I'm trying. Thanks for helping!

Power valve is just the timing related to engine vacuum of when the carb adds extra enrichment. The amount of fuel added when the power valve opens depends on the size of the holes behind the power valve. If someone enlarged the holes it could go rich when the power valve opens. The adjustable metering plates have the holes drilled and tapped for screw in restrictions.

 

[Bird 426]

Unfortunately, for me, I have stumbled into an area that turns my brain into jello. It's no longer a main jet and turning an idle screw in or out. I'm this way with electricity too, checking ohms etc.
My 2 problems are rich and a bog when I go to wot.
Have a fuel pressure regulator , is at 5psi
Duel AFR's, mid 13's at 2000 rpm driving, need to check manifold pressure when driving
FBO Ignition, 22 intial, 34 total
No vacuum leaks, that I can tell
65 mains in carb, 4.5 or 6.5 pv
15/16 manifold pressure
Tall yellow diaphragm springs
It would be interesting if someone was close with the same set up that had no issues and swap ign to see if something was there and then carbs, I'm just in quick sand. I have read articles and tried almost everything. There is only so much you can do here in print or long distance. Wish that it was as simple as removing and installing a hub cap!
I'll keep struggling.
Thank you for the replies !

 

[steve340]

Two carbs is bad enough to sort out an issue but three you really need to know your stuff.

 

[Bird 426]

Agreed. Not looking forward to the day when the time comes to start my Gen ll Hemi. I'm getting tired.

 

[Texas97]

Unfortunately, for me, I have stumbled into an area that turns my brain into jello. It's no longer a main jet and turning an idle screw in or out. I'm this way with electricity too, checking ohms etc.
My 2 problems are rich and a bog when I go to wot.
Have a fuel pressure regulator , is at 5psi
Duel AFR's, mid 13's at 2000 rpm driving, need to check manifold pressure when driving
FBO Ignition, 22 intial, 34 total
No vacuum leaks, that I can tell
65 mains in carb, 4.5 or 6.5 pv
15/16 manifold pressure
Tall yellow diaphragm springs
It would be interesting if someone was close with the same set up that had no issues and swap ign to see if something was there and then carbs, I'm just in quick sand. I have read articles and tried almost everything. There is only so much you can do here in print or long distance. Wish that it was as simple as removing and installing a hub cap!
I'll keep struggling.
Thank you for the replies !

manifold at idle is 15-16? if that's the case, i think your PV is too low, you need it to come in earlier, so a 7.5 or 8. rule of thumb, i thought, was half of idle manifold vacuum.

also, 5 psi seems too low. id be at 6.5 psi. the other 6 pack thread the claim is fuel pressure drops as temp increases.

if both PV and pressure are too low you are super lean at tip in..

what do the spark plugs say?

 

[Bird 426]

I'm rich, really rich. I get tired of messing with it. It's going to be hot for a couple of more days. Will try something else towards the end of the week.
Thank you

 

[451Mopar]

It is time consuming, but I would disconnect the end carbs so they don't open at all. In the center carb plug the power valve, and set idle mixture and synchronize the carb flow at idle. let the car warm up and drive it easy while monitoring the Air Fuel Mixture. It should remain fairly constant with steady throttle, and richen with the accelerator squirt when moving the throttle. Try to get AFR around 14.5-14.7 through a wide RPM band. Best place is on a chassis dyno, but having someone monitor while driving helps.
This is where you want to just focus on the primary carb main jetting, and to see how much AFR varies across RPM in case the air bleeds need correction.
Once that is done, install the power valve. Usually about 1/2 of the idle vacuum.
Repeat the tests and monitor AFR when vacuum dips to where the power valve is open, AFR should goto around 12.8:1. If leaner than 13:1 the holes behind the power valve need enlarged, and if richer than 12.5:1 they need leaned out.
Next would be working on the accelerator pump discharge to where you can stomp the throttle and not bog.
Once the center primary carb is sorted out, re-connect the outboard carbs and see how the AFR is at WOT, and adjust the outer carbs as needed.
Be careful with fuel pressure, the outer carbs (reproduction) have the plastic floats with aluminum hanger arms and the arms will bens with too much fuel pressure.
The tell tale sign is when the carb fuel bowl level keeps creeping up even after adjusting the fuel level and pretty soon you run out of adjustment.
The center carb has a brass float with the brass hanger arms, and it seems to resist bending better than the other floats. You should be OK with 5PSI fuel pressure?
The car I was having issues with had 9 PSI fuel pressure.