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Re: Removing power valve [Re: fast68plymouth] #2649141
04/26/19 07:57 AM
04/26/19 07:57 AM
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varunner Offline OP
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thanks for the link. I've read some about this carb, as far as the mixture screws, I must not have the original metering block because turning the screws in will kill the motor. once I start it today I'll try to lean it out a bit with the mixture screws. I've tried adjusting the screws with a vac gage and the tach, always end up at 1 1/2 - 1 3/4 out for highest idle. Need to find some zinc additive before I start it, ran out of the comp cams additive I've been using.

Originally Posted by fast68plymouth
Okay...... we may be getting somewhere.......

If what’s said in this thread is true....... then some serious reworking of the low speed circuits would have had to be done for this application......
https://www.forbbodiesonly.com/moparforum/threads/pic-request-1971-383hp-with-factory-holley.97491/

Re: Removing power valve [Re: varunner] #2649197
04/26/19 09:54 AM
04/26/19 09:54 AM
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I’d check the sizes of the pri and sec ifr’s and iab’s....... to see if their sizes seem to make sense.


68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
Re: Removing power valve [Re: varunner] #2649316
04/26/19 02:36 PM
04/26/19 02:36 PM
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Val-haul-ass... eventually
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Val-haul-ass... eventually
Originally Posted by varunner
On the secondary metering block, my carb guy asked if I wanted one, he said some guys do it some don't , so I said sure do it. Supposedly only advantage is changing jets. If it doesn't fly I'll remove and put a plate on it. I have another carb getting done without it. So with a plate how do you richen or lean it out ? different plates or can you modify it ?

Aftermarket plates can use standard Holley jets, but you'll need to be sure the jets don't interfere with the float's range of motion.

Check Quick Fuel and AED and see what they offer.

Re: Removing power valve [Re: BradH] #2649395
04/26/19 07:28 PM
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varunner Offline OP
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Thanks for the help so far. So I started it up and set the fuel pressure at 6 psi, seemed stable for the 10 minutes I ran it. You couldn't smell any gas with it idling. I set the mixture at 1 1/4 out. It sounded ok, I shot a video of it idling, but the sound quality is pretty bad. I'll run it tomorrow at a TnT and see how it runs. Afterwards I'll check the plugs and oil. Attached are the specs I got from the carb guy, feel free to comment on it.

20190426_165550_resized.jpg
Re: Removing power valve [Re: varunner] #2649409
04/26/19 08:05 PM
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here's the video, sorry for the camera rotated.

Idle

Re: Removing power valve [Re: varunner] #2660581
05/30/19 11:17 AM
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varunner Offline OP
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I thought I'd update this thread. I've only made a few more passes with this car. At VMP I lower the 60ft. from 1.58 to 1.50. I got rid of the secondary metering block and have been working on closing the throttle plates to close up the transfer slots. I opened up the holes in the throttle plates to .150" and was able to close up the transfer slot to @.050" I further opened the holes to .180" which is I think alot. This did not allow me to close the transfer slots up any more, so I think I'm done there. Would opening the idle air bleed help with this effort ? The main issue is still there and that is liquid fuel in the plentum floor of the intake and fuel fowled plugs.
This is interesting, I had a sample of the oil tested. They could not find any fuel in the oil, but they did find lead and water. I think and hope the lead and water are from the fuel, sunoco 110. The last thing I want to mention is that, is it possible that the fuel in the intake and plugs are because of blocking the heat crossover in the intake ? The heat is to atomize the gas as I understand. So maybe a hotter plug is all I need to do........

Re: Removing power valve [Re: varunner] #2660997
05/31/19 05:02 PM
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Imo, this a classic case of where substituting a “known good” part would help shed some light of where to look.

My suggestion is to see if maybe one of your racing buddies has a known good working bracket race carb with 4 corner idle you could put on the motor........ run it for a while, get the motor up to operating temp, etc...... then pull it off and see if the manifold is wet like with the other carb or not.

If the plugs aren’t wet, and the manifold looks normal....... you know it’s simply a carb issue, and can stop looking at other items as being where the problem is.

From this side of the keyboard...... I’m betting it’s a carb issue.

My 383, which had a bigger cam than yours, and blocked heat crossover didn’t have a wet manifold plenum, and the same set of plugs were used for well over 100 dyno pulls and probably 200 passes in the car(3 seasons)....... and still looked fine.
Also...... with regards to the blocked heat crossover....... my guess is virtually every good running stocker has a blocked heat crossover(not to mention the countless other race car motors that use “air gap” style manifolds without crossover heat).

Of course, I had a good working carb with low speed calibration suited towards poor carb signal at lower rpms.

I won’t get into a debate over it, but the 2.5pv isn’t what you want.


68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
Re: Removing power valve [Re: fast68plymouth] #2661007
05/31/19 05:54 PM
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varunner Offline OP
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I agree with ya Dwayne. The atomization thought is just drawing for straws. Anyway, I made some progress. Someone suggested I check the body and baseplate of the carb for flatness. I did and the body was warped .011" So re-assembled it and I cranked down on the screws best I could without striping the threads, put it back together and ran it. The last few times I've run this engine,the vacuum floats from 8-12 in. with the rpm tracking the the vacuum. Took off the carb and there was still fuel in the intake, maybe a little less. I took the carb base plate off and the base, body, and gasket were pretty much dry. Previously they were soaking wet. Far from a slam dunk, but it's worth pursuing. I think I will try to re-surface the body and get a new gasket.

Any suggestion on a PV ?

Re: Removing power valve [Re: varunner] #2661026
05/31/19 07:21 PM
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The only thing a PV will do for that application is help keep the plugs cleaner when you’re putting around the pits.

I like the rating to be pretty high so it opens early on in the throttle opening at the starting line.

I’d also prefer it not to be real close to the vacuum reading at idle, if possible, so it doesn’t fluctuate open/closed during idle.

I’d be using something around 6.5-8.5........ and if it’s just open all the time at idle, that’s fine(usually helps with throttle response in that type of application).

Without seeing the carb myself and what’s been done to the low speed circuits, my suspicion is that the conversion from a “reverse” idle circuit to a “normal” idle circuit isn’t quite right for the application.
I’d want the primary idle/transition circuit(including ifr/air bleed sizing and placement) to be laid out just like a normal non-emmisions calbrated carb is.

In having messed with this stuff for almost 40 years........ my experience is that nothing is better for isolating a potential carb problem...... to the carb............than swapping it for a known good carb.

Basically, my viewpoint is........ if you put something like a QFT Q-750 on it......., assuming that carb was working as it was intended to........ the wet plenum and fouled plugs would go away.
And if that happened, you’d know the problem was strictly a carb issue.


68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
Re: Removing power valve [Re: fast68plymouth] #2661029
05/31/19 07:35 PM
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Here’s a post I made recently on another board about the value of the known good carb:

Quote
As a slightly off topic example of the value of “known good”.....

I tested a motor for a customer who had several new carbs to try, and one other which was supposed to be known good.
It was a new motor combo, so no previous history to judge by.
Started with the known good carb........ carb seems to need an abnormal amount of jet to get a/f ratios where they should be, and then starts to become somewhat numb to increases in jet.
We’ve got lots of carbs to try......so, install another one....... and then one or two more.
All were different Venturi diameter sizes, along with different booster configurations.

They all exhibited the same two qualities....... really really rich at part throttle...... all took way more jet than they should have to get the a/f ratios where they should be...... and were still kinda lean.......with a gradual leaning out throughout the pull.

Well, as it turned out, the known good carb had the main body substituted....... so it wasn’t exactly the known good carb anymore.

At the end of the day, we installed one of my “known good” dyno carbs.
No problems with the overly rich part throttle operation, and it didn’t require any jet changes at all to have normal wot a/f ratios.
In fact it was the richest of all the carbs tried, with way way smaller jets in it.
This carb has a tendency to slightly richen as the rpm increases, which it did on this motor as well....... the exact opposite of the tendency of the other carbs.

Prior to installing that last carb, there was speculation that perhaps the new combo was presenting some sort of unique fuel delivery issue that the carbs were having a hard time coping with.
In the end, that wasn’t the issue at all........ it was just the other carbs tunes were all that far off.
Which was made instantly clear once the motor was run with the “known good” carb.


68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
Re: Removing power valve [Re: fast68plymouth] #2661037
05/31/19 08:31 PM
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varunner Offline OP
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Agreed, it's the first thing I'd try if I had one. When I first got this carb back, I couldn't get it to idle under 2K, in order to diagnosis that I borrowed a carb that was just "re-built", it was in bad shape, coughing and back-firing. So I had an old 600 that I put on, it had multiple leaks. Nothing else local to pick from. So if I had a carb that I knew was good I'd put it on, but doing so wouldn't tell me much about the one I'm trying to fix. I'm all for swapping parts, but I'm sure my current carb is the issue. I have another carb getting done and will have it a few weeks. Looking forward to that. But I do think I'm on the right track, at least I hope so. I re-finished the carb body tonight and will try it tomorrow, although I don't have a new gasket yet.

Thanks for the tip on the PV

Re: Removing power valve [Re: varunner] #2663373
06/07/19 08:50 AM
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Ok, I have finally found the real issue here. I did end up re-surfacing the bottom of the body and that is sealed up well. My original thought was to take out the power valve, I never tried that. So after looking at the baseplate, a lightbulb flickered on. First picture shows how I originally had it put together, second one is the fix.

20190606_151045_1559910040586_resized (2).jpg20190606_151106_1559910039122_resized (2).jpg
Re: Removing power valve [Re: varunner] #2663388
06/07/19 09:35 AM
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I’m not sure what I’m supposed to be looking at that would make the light bulb turn on......... but I doubt from the factory they came with an open gasket installed between the carb and manifold.
Not that it shouldn’t work fine....... just that they also worked fine without it.


68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
Re: Removing power valve [Re: fast68plymouth] #2663393
06/07/19 09:47 AM
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varunner Offline OP
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The first gasket blocked off the passage that delivers manifold vacuum to the back side of the power valve. Manifold vacuum is what keeps it closed. The original gasket and insulator were open, not 4 hole.

Re: Removing power valve [Re: varunner] #2663397
06/07/19 09:50 AM
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Originally Posted by varunner
The first gasket blocked off the passage that delivers manifold vacuum to the back side of the power valve. Manifold vacuum is what keeps it closed. The original gasket and insulator were open, not 4 hole.


I don't think the gasket blocked anything off. Those channels expose the power valve port to manifold vacuum regardless of the gasket sitting on top of it.


Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
Re: Removing power valve [Re: varunner] #2663399
06/07/19 09:51 AM
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The first gasket does not block that cavity.
That’s what the “x” channel cut into the baseplate is for.

Furthermore....... the PV is not part of the idle circuit....... so open or closed....... does not affect the idle A/F ratio.
So, if the motor is loading up the plugs while idling...... the PV is not the source of the extra fuel...... unless it’s leaking fuel past the gasket or is torn.

But....... you’ll know shortly after you’ve got it running again if you’ve solved the problem or not.


68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
Re: Removing power valve [Re: fast68plymouth] #2663406
06/07/19 10:06 AM
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Well, the only way I can see on this carb for the PV to get vacuum is from the opening in the base plate that was covered. And if the power valve is open, that fuel would be coming out of the booster, correct ? What I know for sure is that the idle changed a bunch with the other gasket, and the manifold vacuum also stabilized. Before it would stay above 10 in. then drop to about 5 in. and the motor would almost die, then it would cycle back and forth. now it's rock solid at 9 in. plugs are dry now too. I'm not a carb expert, but changing the gasket made a big difference, that's for sure.

Re: Removing power valve [Re: varunner] #2663407
06/07/19 10:08 AM
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oh, and to add, I called holley and asked if it was a reverse idle carb and they no. hard to find any info on this carb for some reason. R-4668

Re: Removing power valve [Re: varunner] #2663413
06/07/19 10:19 AM
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I’ve seen things solve problems before, when they shouldn’t have.

But as has been said, the x channel that’s connected to that PV signal cavity in the carb is only there to provide access to vacuum for that cavity when a 4 hole gasket is employed.

Did you try the carb with the 4 hole gasket after you milled the baseplate?
The open gasket looks a lot thicker and more compliant than the 4 hole you’re using.

My guess is if you installed a std 4 hole gasket made out of the same material, and the same thickness as the open gasket you have...... it would run the same.

I’ll add this...... all Holley 4bbl carbs use that cavity for the PV vacuum...... and they all seem to retain PV functionality just fine when used with a 4 hole gasket.

The only reason I thought it had the backwards idle circuit was because of the info provided in the link I posted, which seemed like it was coming from someone well versed in that particular carb.
I’ve never had one of that list number carbs in my hands.

9” of idle vacuum is surprisingly good for that combo.

Quote
And if the power valve is open, that fuel would be coming out of the booster, correct ?



The fuel that gets added to the main circuit by the PV would only be coming out of the booster(along with the fuel from the main jet) if enough air is flowing through the Venturi to activate the main circuit.


68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
Re: Removing power valve [Re: varunner] #2663425
06/07/19 10:57 AM
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I don't like to use the 4 hole gasket unless you use a 4 hole space or the intake supporting it.the gasket could get sucked in the engine.


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