Power valve
- Thread starter Bird 426
- Start date
Canadian1968
Well-Known Member
Probably not a good idea !
steve340
Well-Known Member
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.
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.
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!
Thanks for helping!
451Mopar
Well-Known Member
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.
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 !
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
Well-Known Member
Two carbs is bad enough to sort out an issue but three you really need to know your stuff.
Texas97
Well-Known Member
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?
451Mopar
Well-Known Member
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.
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.
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BSB67
Well-Known Member
To the OP, you’ll need to provide much more description and details around your two problems if you want meaningful help. Assuming there isn’t anything wrong with your carbs (other than tuning) your two issues are likely unrelated.
Exactly when is it rich, and how do you know? There are essentially 4 different circuits that can affect the A/F ratio at different operating conditions.
Describe in detail when and how the bog presents. We need to establish if it’s a problem with the center carb, or the rate at which the outboards come in. The latter is common when dropping the hammer from a roll when using the yellow tip springs in the outboard carbs. Car weight, gear and converter will effect this as well.
I’ve run the 6 pack set up on mild and wild 383, 440’s and 500 inch roller cam motors. My general take-away is that it is surprising how little adjusting is needed.
Exactly when is it rich, and how do you know? There are essentially 4 different circuits that can affect the A/F ratio at different operating conditions.
Describe in detail when and how the bog presents. We need to establish if it’s a problem with the center carb, or the rate at which the outboards come in. The latter is common when dropping the hammer from a roll when using the yellow tip springs in the outboard carbs. Car weight, gear and converter will effect this as well.
I’ve run the 6 pack set up on mild and wild 383, 440’s and 500 inch roller cam motors. My general take-away is that it is surprising how little adjusting is needed.
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#13. Yes, it is amazing to me how some have little to no problems, and like me, nothing but problems.
I need to do more testing as suggested here.
I have come to not trust the AFR's, plus they always are fouling, don't think that they like carbs!
The car is a '69 Dart, 4-speed, 3:55's, 255x60x15 SS street radials
I don't know how far to go into car/engine details here, but I can.
Stroker SB, 418, trick flows, roller cam, whole engine spec'd out by B3. I don't or haven't bothered Mike about tuning, the Sixpack wasn't his choice for carburation.
The bog is a hit at 2,500 rpm. If I walk in at say half throttle, I can feel the ends coming in without hesitation, that was kinda a test, I didn't stay in it. Sorry, keep forgetting to look down at the AFR's when I hit it, things happen fast.
I'm going to try post #12's suggestions
Also need to get 2 or 3 sets of new spark plugs. I haven't gone out and did a wot hit, shut it off and check the plugs.
Everything right now is about the same as when I first built the engine and it ran fine, but rich, no hesitation at the hit.
I will stay in touch and try and write all of this down. Or we can exchange phone numbers.
Thank you guys! But I too seem to have a bog! I have 3 cars, you that have more than one know that it's difficult to keep them maintained. The Hemi Road Runner isn't even together yet, and it has definitely been a distraction.
I need to do more testing as suggested here.
I have come to not trust the AFR's, plus they always are fouling, don't think that they like carbs!
The car is a '69 Dart, 4-speed, 3:55's, 255x60x15 SS street radials
I don't know how far to go into car/engine details here, but I can.
Stroker SB, 418, trick flows, roller cam, whole engine spec'd out by B3. I don't or haven't bothered Mike about tuning, the Sixpack wasn't his choice for carburation.
The bog is a hit at 2,500 rpm. If I walk in at say half throttle, I can feel the ends coming in without hesitation, that was kinda a test, I didn't stay in it. Sorry, keep forgetting to look down at the AFR's when I hit it, things happen fast.
I'm going to try post #12's suggestions
Also need to get 2 or 3 sets of new spark plugs. I haven't gone out and did a wot hit, shut it off and check the plugs.
Everything right now is about the same as when I first built the engine and it ran fine, but rich, no hesitation at the hit.
I will stay in touch and try and write all of this down. Or we can exchange phone numbers.
Thank you guys! But I too seem to have a bog! I have 3 cars, you that have more than one know that it's difficult to keep them maintained. The Hemi Road Runner isn't even together yet, and it has definitely been a distraction.
Texas97
Well-Known Member
im following this whole heartedly. i built my 6 pack setup based on what i have in my Charger now, vacuum etc. But ive not run it yet. Will be installing in the next few weeks.
@Bird 426
quick question, when was the last time you checked timing? what's your initial timing and your all- in timing?
@Bird 426
quick question, when was the last time you checked timing? what's your initial timing and your all- in timing?
BSB67
Well-Known Member
Good grief.
You still have not answered the question of when is it rich, and how do you know it’s rich. Dont say “the plugs”, as that is not helpful. Here, for starters, pick one of these three, idle, or cruise, or WOT.
Knowing your cam specs would be helpful too
Your bog at stab at 2500 rpm is one of two things: 1) center accel pump, or 2) outboard diaphragm springs are too light. First check that the pump is adjusted properly and is squirting, then put the black springs in the outboard diaphragms, as a test.
You still have not answered the question of when is it rich, and how do you know it’s rich. Dont say “the plugs”, as that is not helpful. Here, for starters, pick one of these three, idle, or cruise, or WOT.
Knowing your cam specs would be helpful too
Your bog at stab at 2500 rpm is one of two things: 1) center accel pump, or 2) outboard diaphragm springs are too light. First check that the pump is adjusted properly and is squirting, then put the black springs in the outboard diaphragms, as a test.
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The spark plugs are black with soot. Shows up driving or wot, do not know about idle, do not check them at idle. Until this problem showed up, the tall yellow was fine, that is why I haven't gone to a brown or black.Currently has a purple.
The accelerator pump is working, white cam, same as when it ran good
Cam is Howard's hyd. roller, 1.6 rockers
see cam specs
AFR'S
Idle, mid 14's
Cruise at 2000 rpm. Mid 13's
Wot, not sure with current jetting, have just been driving on the 2 barrel
Plug picture is #8 and #1
It's difficult here to say all of the things that I have done, because a lot of it to me gets contradictory. That's why I am so confused, there's a variable that I can not put my finger on.
Once I pig richened it across the board, at the hit at 2,500 it ran like it did the first time out, great, I've found it, but the next time that I drove it, it was just rich with the same bog.
I'm sorry, but something is wrong that is going to be difficult here to find. I'm 75, and with 95° temps here, I'm not running out here to work on it with a hot engine.
I know, your trying too.
The accelerator pump is working, white cam, same as when it ran good
Cam is Howard's hyd. roller, 1.6 rockers
see cam specs
AFR'S
Idle, mid 14's
Cruise at 2000 rpm. Mid 13's
Wot, not sure with current jetting, have just been driving on the 2 barrel
Plug picture is #8 and #1
It's difficult here to say all of the things that I have done, because a lot of it to me gets contradictory. That's why I am so confused, there's a variable that I can not put my finger on.
Once I pig richened it across the board, at the hit at 2,500 it ran like it did the first time out, great, I've found it, but the next time that I drove it, it was just rich with the same bog.
I'm sorry, but something is wrong that is going to be difficult here to find. I'm 75, and with 95° temps here, I'm not running out here to work on it with a hot engine.
I know, your trying too.
steve340
Well-Known Member
From what you have written - this carb set-up once ran good - correct?
If so start with the float adjustments on all three carbs.
Check the carb air bleeds are not blocked.
Test and see what has happened - same, better?
If so start with the float adjustments on all three carbs.
Check the carb air bleeds are not blocked.
Test and see what has happened - same, better?
Yes, that is correct, it hit like a freight train. I checked the floats about a week ago, bottom of the sight hole, but the engine wasn't really heat soaked, will check that and fuel pressure again.
I do the air bleeds check on the end carbs for fuel/air screws, Promax base plates.
Yes, I probably should take the carbs apart, soak and clean. Some people say that the ignition can act similarly, but don't believe that is it. When it hits after the bog, it's not running like before the problem started.
I do the air bleeds check on the end carbs for fuel/air screws, Promax base plates.
Yes, I probably should take the carbs apart, soak and clean. Some people say that the ignition can act similarly, but don't believe that is it. When it hits after the bog, it's not running like before the problem started.
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