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Determining correct power valve

OH71RRunner

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Quick background
440 .030 over. Around 11:1 CR
MP 509 cam
6BBL
727 with reverse manual
Used to have horrible overheating problems. That seems to be taken care of. Had timing issues. Again, seems to be rectified now. Timing is around 16 initial and all in around 2200 RPMs at 34. I don't remember exactly what the timing is. It starts fairly easy when hot and no run on when turned off. I was having what sounded like spark knock at WOT. Now it feels like it runs out of gas during WOT run after going through the gears. It falls flat on its face above 3500 RPMs in 3rd. Does great from 1st to 2nd. Can feel it falling off when I shift into 3rd.

Outboard carbs metering plates drilled by ProMax years ago
Rebuilt couple times with new gaskets last year. Twice.
Trying to get the carbs set. Main jets are 65 I believe. Power valve is 4.0. I think I should go up to 4.5 or 5.0. I was at the 5.0 but idle was really rich. Burn your eyes rich. I could lean it out a little, but the idle screws were out somewhere around 4-5 turns out. Still rich.

I finally got around to hooking up a vacuum gauge and taking it for a drive. I'm not sure I did it right, but this is what I did: tee'd vacuum between back of intake and brake booster. Taped gauge to windshield and recording readings at different times. Had the mrs. with me to write things down so I didn't have to remember. Lol
This was done after the car was warmed up to proper temps.
*Warmed up idle before driving - 7 in hg
*55mph 2500 RPM (part throttle cruise) - 14 in hg
*WOT in 3rd - 4 in hg
*Decelerating from above it went up to 16 in hg
*2nd to 3rd WOT - 4 in hg
*Part throttle in 3rd 65mph 3200 RPM - just shy of 15 in hg
*2nd gear deceleration - jumped up to 17 in hg
*WOT from dead stop - 4 in hg

After driving for about 30 minutes:
*In neutral - 8 in hg (but was increasing)
*In gear - 5 in hg
*Idling in gear is about 850 RPM
*Idling in neutral is about 11-1200 RPM

So the main question is do I need to go back to 5.0 PV and try to adjust outboards leaner, try the 4.5 again and retune, or do I have other issues?

Sorry for such a long post.

I'm still trying to learn about carburaters. I know I'm overlooking something.
Hope you all can help me figure this out.
 
I’m still trying to visualize all ur numbers; decel numbers don’t mean a thing, disregard those. Probably try the 4.5pv. Fuel pump rod worn limiting the volumn from fuel pump? (I’m still running my original pump rod with 86K on it). Also can’t comment on jetting for 6paks, sorry. What do the plugs look like & what rear gear?
 
Power valve has nothing to do with it falling flat on it face at 3500 in 3rd gear. It only opens when the vac gets below the # on the valve, and it would already be open by then if you have it floored. I have not had a vac gauge on a motor with that cam, but do those readings sound low at idle? I just put an AEM air fuel meter in 2 of my cars, and honestly don't know how a guy can properly tune a car without one.
 
Power valve has nothing to do with it falling flat on it face at 3500 in 3rd gear. It only opens when the vac gets below the # on the valve, and it would already be open by then if you have it floored. I have not had a vac gauge on a motor with that cam, but do those readings sound low at idle? I just put an AEM air fuel meter in 2 of my cars, and honestly don't know how a guy can properly tune a car without one.
Weeelll, it’s reading plugs,listening to the engine & a lot of ‘shadetree’ tuning. I’m still trying to figure out(remember?) how we did all of that with no internet help!
 
3:91 rear
I didn't check the plugs after driving hard today. I did check them the other day after a few drives. They were clean and looked normal.
The fuel pump rod and fuel pump were replaced last year because of similar issues. Carter mechanical pump and hardened rod from Jegs. Can't remember which brand it was.
 
Weeelll, it’s reading plugs,listening to the engine & a lot of ‘shadetree’ tuning. I’m still trying to figure out(remember?) how we did all of that with no internet help!

LOL. What I meant to say is that an A/F gauge really makes the tuning process a whole lot easier.
 
I'll throw this out to you. 71 440, 6bbl, 292°/.509" purple stripe cam in a 70 V-code RR. FBO ignition system 4.10 Dana, 5 speed. I changed out #62 jets I found in the center carb for #65 which is 1 number richer than the stock standard transmission #64.
Stock 6bbl about to go to Promax for a lot of their parts, for greater tuning flexibility and performance, but they currently work pretty well on the butt dyno.
Sounds like the center carb idle screws are way too far out. IIRC mine are closer to 3 turns out, if that.
Have you used the "finger blocking the idle bleeds" on the outboard carbs to set the outboard carbs idle mixture screws? Turn them a LOT less at a time to adjust.
Float levels ok?
 
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If your cruise vacuum is 14 inches you should be running a power valve around 8 to 10 inches. Your wide open in 3rd gear is 4 inches vac and the power valve is set to 4 or 5 is not opening. So no extra fuel until the secondaries open.
 
I have worked a LOT with Holley carbs over the years. The thing about power valves is that generally, they should be one of the last things you should worry about when tuning.
My best suggestion would be to put the 'stock' sized power valves in (likely the 6.5) and tune everything else before fooling around with the power valves. Most people don't even understand what the power valves do in the carb, but when in doubt, put a higher number in. Then tune other stuff before going back to the power valves.
 
I have worked a LOT with Holley carbs over the years. The thing about power valves is that generally, they should be one of the last things you should worry about when tuning.
:lowdown: regarding working with Holley carbs a LOT over the years.
Power valve # from lots and lots of reading should be 1/2 of vacuum at idle is what I have often 90+% of the time read.
I first knew I had a problem with the outboard carbs idle mixture screws when I screwed my center carb's idle mixture screws all the way in on both sides and the engine kept running, at least as well if not better than before.
Too much fuel/air? being added by the outboard carbs. I still have a problem with my carbs "creeping to too rich" over time, at least it seems that is what is happening.
Setting the idle mixture screws on the outboard carbs using the blocking of the air bleeds with your finger method was an epiphany for me.
This was the paragraph that led me to the method of tuning the outboard idle mixture screws:
20180625_220650.jpg

I plan time on a chassis dyno near my after Promax "does their thing" and I am also installing the "legendary" Carter M6903 mech fuel pump in this "round" of mods.
I'm not saying that has anything to do with your problem, I still would check float levels to be sure they are allowing enough fuel to be "stored" in your fuel bowls, and also fuel filter and or fuel vapor separator if you have one because it has a screen filter in it from what I understand.
When the Mopar/Edelbrock/Holley 6bbl is right, the rush of power (on my modest motor) is amazing and in my case I guess I have to credit the cam headers and intake systems for it pulling HARD to 6,100 with no discernable fall off in power. I have my shift light set at 5,800 and my rev limiter set at 6,200. The chassis dyno will tell me the "truth" about my A/F ratio and power band (H.P. and Torque). I would know more too about condition of tune if traction wasn't such a problem off the line thru 1st gear. I don't regret switching from stock 3.54s to 4.10 ring and pinion gears a few months after my Passon 5 speed went in, because 4.10 + .70 5th is 2,750 RPM at appx 75 vs 3,500 RPMs at 75 in 4th w/my 3.54s. It's a LOT more "fun" but certainly made 1st gear traction a greater challenge. Anything over 1,200 RPMs off the tree and I get wheel spin. My 315/35/17 Toyo Proxes TQ drag radials try, and do a hell of a lot better job than the old 285 15s T/A Radials did, but grip is elusive.
If anyone wants to try "fuel injection", in a 6bbl, this FiTech is the least expensive option by far that comes as a system, and other than an electronic fuel pump and electronic distributor you need for it to be "complete", the system comes in WAY less than any other system. If I wasn't $750 in already committed to what Promax is going to do, I may be looking hard at this FiTech.
https://fitechefi.com/products/39610/
 
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I'll throw this out to you. 71 440, 6bbl, 292°/.509" purple stripe cam in a 70 V-code RR. FBO ignition system 4.10 Dana, 5 speed. I changed out #62 jets I found in the center carb for #65 which is 1 number richer than the stock standard transmission #64.
Stock 6bbl about to go to Promax for a lot of their parts, for greater tuning flexibility and performance, but they currently work pretty well on the butt dyno.
Sounds like the center carb idle screws are way too far out. IIRC mine are closer to 3 turns out, if that.
Have you used the "finger blocking the idle bleeds" on the outboard carbs to set the outboard carbs idle mixture screws? Turn them a LOT less at a time to adjust.
Float levels ok?
Yes, finger over air bleeds on outboard carbs with no change. So those should be good. Fuel float level is just touching the bottom of the hole on all three. Since I went to the 4.0 PV, my idle adjustment screws are about 2 1/2 turns out. All the way in, and it'll die.

If your cruise vacuum is 14 inches you should be running a power valve around 8 to 10 inches. Your wide open in 3rd gear is 4 inches vac and the power valve is set to 4 or 5 is not opening. So no extra fuel until the secondaries open.
When using the 5.0 PV, the idle was crazy rich. Had to back out idle screws a lot and still was rich. I didn't drive it like that though. Should I try it being that rich? I guess I could have had a bad PV.


64 jets were in it and had pinging at WOT. PV was 5.0. That's why I went to the 65s and tried the 4.0 PV. I switched out to the 4.5 and I'll test it tomorrow.

Trial and error. Lol

Thanks for the responses. Keep them coming as I'm willing to try just about anything to get this thing running right. It's been in the garage far too long with silly issues and I'm ready to get out and drive this thing.
 
Fuel float level is just touching the bottom of the hole on all three.
My understanding is the outboard carbs float fuel level set properly, that level should have fuel coming out of the bottom of the level check "holes" if you don't have clear plug windows to visually check them. Center carb fuel level at bottom of the level check "hole".
The outboard float levels sound a little low, and that really sounds like that could be the problem!
 
The power valve has no effect at idle. If you are sure it is to rich, check to make sure that the gasket on the PV was installed correctly. Also the Promax metering plates can cause the PV to have interference problems and cause gas to leak into the intake. Your idea for using vac meter while cruising was excellent and I have done it for years. I highly recommend O2s for tuning, takes a lot of guess work out of the process.
 
QUOTE="biomedtechguy, post: 910992407, member: 16322"]Backing out idle screws (counterclockwise)
adds fuel, unless I had recent brain damage and am blissfully unaware of it.[/QUOTE]
Thanks for catching that. My mistake. Idle screws didn't do much with 5.0 PV unless it was almost all the way IN. The 4.0 PV and 64 jets the screws were out a lot.
I should've checked my notes before posting. I've done so much trying to get these carbs set right.


I should probably go back to square one and start over again since I continue to learn more and more about these things. My neighbor keeps preaching and pushing for fuel injection. I know that would be easier, but I can't give up yet.
 
My neighbor keeps preaching and pushing for fuel injection. I know that would be easier, but I can't give up yet.
When the Mopar/Edelbrock/Holley 6bbl is right, the rush of power (on my modest motor) is amazing
Hang in there.
BUT...
If you get to the point where you just can't take it anymore:
This is pretty badass, WAY less $$ than other F.I. options, and I even know an authorized dealer who is OUTSTANDING on knowledge and tech support, and may be able to save you some money too. PM me if you want his contact info.
https://fitechefi.com/products/39610/
 
Hang in there.
BUT...
If you get to the point where you just can't take it anymore:
This is pretty badass, WAY less $$ than other F.I. options, and I even know an authorized dealer who is OUTSTANDING on knowledge and tech support, and may be able to save you some money too. PM me if you want his contact info.
https://fitechefi.com/products/39610/
I love the look of that setup. IF I ever decide to go fuel injection, that's definitely the way I'd go.
 
You shouldn't be that far out on the idle screws. If more than 2 turns out, the outboards need to contribute more fuel at idle. As far as the power valve is concerned I agree it has nothing to do with idle but the correct valve should be at least 2 numbers less than whatever your vacuum reading is at idle. Now on to the falling flat, if you are sure the float levels are correct in all the carbs and you are maintaining good fuel pressure then you might take a look at the diaphram springs in the outboards. When you say it falls flat do you mean it just has no power or there is a momentary bog?
 
Have you indeed verified it is not running out of gas by the time you get into 3rd? May want to add a fuel pressure gauge and verify you have enough pump. Also given the fact you have 4” vacuum at WOT would indicate the carbs are not going wide open.
 
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