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Re: How do you have your Holley Double Pumper tuned? [Re: radar] #1516152
10/15/13 10:26 AM
10/15/13 10:26 AM
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Benton, IL.
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DaveRS23 Offline
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Just to be safe, I usually use a single wire that runs from one opening to the other. That works for me for all the metering orifices,the IFRs IABS, PVCRs, etc. The longer wire is much easier to handle and has little or no chance to disappear.


Master, again and still
Re: How do you have your Holley Double Pumper tuned? [Re: ONEBADBIRD] #1516153
10/15/13 05:41 PM
10/15/13 05:41 PM
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Balt. Md
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383man Offline
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Quote:

School me on what IFR's are? ,and why should I wire them down? In your earlier post, you mentioned PVCR's also? Power Valve Circuit something? Still learning these acronyms. Thanks, Jay




You dont have to wire them down as DaveRS23 explained what you do is insert a piece of wire a certain size in the IFR (Idle Fuel Restricter) which takes up space and lets less fuel get through that circuit and leans out the idle. Its an old trick Bill Jenkins use to do back in the 60's and 70's and it works. All the newer cars already have jets in the IFR and the PVCR and on the newer carbs all you have to do is change the jets. In fact most newer carbs have jets in the ildle air bleed and high speed air bleed circuits also for easy tunning. Ron

Last edited by 383man; 10/15/13 05:43 PM.
Re: How do you have your Holley Double Pumper tuned? [Re: DaveRS23] #1516154
10/15/13 05:45 PM
10/15/13 05:45 PM
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383man Offline
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Quote:

IFRs are the Idle Fuel Restrictors. One for each barrel. They meter the fuel to the idle screws. The Idle Air Bleeds in the throat of the carb meter the air. Together, they provide the ratio for the idle mixture. The adjustment screws are simply a volumn adjustment.

If your adjustment screws are only 3/4 turns or so out, then the mix is usually too rich. If so, then you can either size the IFRs down or you can open up the IABs. I like to size the IFRs down first, that way I don't mess with the timing of the main circuit.

The proper way to adjust the jetting on the IFRs is to drill and tap them for jets. But what I do is to mike a bunch of strands from some 12 to 16 guage electrical wire and use pieces of that inserted in the IFRs to see what the engine likes. Quick, easy, cheap and effective.

I leave them in when I get them about right, but a guy could go back and drill and tap them for the jets.

PVCRs are the Power Valve Channel Restrictors. They are the holes under the power valve and are essentially jets. The main jets plus the PVCRs add up to the total amount of fuel being fed. Which is why you step the mains up when you block off the power valve. The mains must be larger to compensate for the PVCRs no longer flowing any fuel.

The PVCRs can be drilled larger if the main jets are stepped down or can be wired down if they are too larger and providing too much fuel. Either way, the mix overall (mains + PVCRs) usually needs to remain about the same.

Holleys, in my experience, are usually close at Wide Open Throttle. But need a lot of help in the low speeds, transitions and cruise. Which is where a street car spends most of it's time. There are many, many combinations in these circuits on any given size carb. Which is why all carb manufacturers make street and track versions of the same size carb. It is not just about mechanical or vacuum secondaries.

Track oriented carbs like the DPs, are much richer in these areas than a street carb needs to be. For one thing, a track carb isn't too concerned about cruise.

Do you have Emanuel's Holley book? You will need it. And if you are going to experiment with the IFRs, IABs, and PVCRs, you will need to get familiar with Pi x r2. That gives you the area of the holes you will be modifying. So you know how much bigger or smaller you have made the flow.

This may be the longest post I have ever made. It had better help!




This is good info. Ron

Re: How do you have your Holley Double Pumper tuned? [Re: DaveRS23] #1516155
10/15/13 05:49 PM
10/15/13 05:49 PM
Joined: Oct 2003
Posts: 3,999
South Park, Pa.
68LAR Offline
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Quote:


IFRs are the Idle Fuel Restrictors. One for each barrel. They meter the fuel to the idle screws.


Not quite, They meter fuel to the transission slots.
The transission slots are the discharge ports for the intermediate circuit.


4 speed street legal. Best time 10.99 @ 124 mph on 93 octane pump gas @ 3926# total weight
Re: How do you have your Holley Double Pumper tuned? [Re: 383man] #1516156
10/15/13 10:00 PM
10/15/13 10:00 PM
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Benton, IL.
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DaveRS23 Offline
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Quote:

Quote:

School me on what IFR's are? ,and why should I wire them down? In your earlier post, you mentioned PVCR's also? Power Valve Circuit something? Still learning these acronyms. Thanks, Jay




You dont have to wire them down as DaveRS23 explained what you do is insert a piece of wire a certain size in the IFR (Idle Fuel Restricter) which takes up space and lets less fuel get through that circuit and leans out the idle. Its an old trick Bill Jenkins use to do back in the 60's and 70's and it works. All the newer cars already have jets in the IFR and the PVCR and on the newer carbs all you have to do is change the jets. In fact most newer carbs have jets in the ildle air bleed and high speed air bleed circuits also for easy tunning. Ron




You are right that you do not have to wire them down. You can buy a hand full of numbered jets or blanks and wire drill bits.

Guess which way is quicker and cheaper?


Master, again and still
Re: How do you have your Holley Double Pumper tuned? [Re: 68LAR] #1516157
10/16/13 01:14 AM
10/16/13 01:14 AM
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Balt. Md
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383man Offline
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Quote:

Quote:


IFRs are the Idle Fuel Restrictors. One for each barrel. They meter the fuel to the idle screws.


Not quite, They meter fuel to the transission slots.
The transission slots are the discharge ports for the intermediate circuit.





Some Holley four barrel carbs have seperate idle and transfer circuits and they have seperate air bleeds. Its not the same as the intermediate circuit on the Dominators.
Funny how Holley will run seperate circuits on some models. Ron

Re: How do you have your Holley Double Pumper tuned? [Re: 68LAR] #1516158
10/16/13 02:59 AM
10/16/13 02:59 AM
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Philadelphia
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radar Offline
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Quote:

Quote:


IFRs are the Idle Fuel Restrictors. One for each barrel. They meter the fuel to the idle screws.


Not quite, They meter fuel to the transission slots.
The transission slots are the discharge ports for the intermediate circuit.




Well...

The slow air bleeds also called the Idle Air Bleeds combined with the Idle Fuel Restrictions work together to create an emulsion or fuel/air milkshake. The richness or lean-ness of this mixture is determined by the ratio of these air and gas jets.

This emulsion is delivered in whatever quantity your motor can suck from the transfer slots at low throttle openings before the mains come on. The same emulsion comes from the idle discharge holes (sorry don't know the fancy acronym for that one). The corner idle screws, often called idle mixture screws by some, cannot change the a/f ratio of the emulsion. They do not mix anything they just act like a valve on a garden hose- you should be able to turn them off and kill the motor.

Looking at your carb from below the butterflies at idle you'll see the idle discharge holes and if the curb idle is set correctly you'll see around .030 or a square section on the transfer slot. If you show too much slot below the butterfly at idle it will overwhelm your idle discharge fuel and render the corner 'mixture' screws useless because the motor will suck on the t-slot for idle. Thats why sometimes you need to open the secondaries a hair at idle too.

To a certain extent the circuits all stack up- idle, transfer slot, main jet, and on low vacuum the power valve. Thats why you should get your timing right, then your idle 'mix' screws for max vacuum, then tune the T-slot for clean low throttle cruise, then go back and reset the idle screws, see how low you can get the main jets and drive like an old lady, then get the power valve to help out when you need a little more power, then tune the squirters and secondary mains for tire shredding.

This is a rare thread when I was looking for this info I got kinda vague responses and had to spend a lot of nights pouring over holley books and internet misinformation. Once I figured a few things out folks seemed to act like it was common knowledge! "Of course you have to restrict the IFRs on a street car with a holley DP"

You seem to be asking good questions and getting great answers. Please use this info as a jumping off point for your tuning- get in there and try some stuff and come back and let us know how it worked for you. Then later other folks can search and find this stuff out too

Radar

Re: How do you have your Holley Double Pumper tuned? [Re: radar] #1516159
10/16/13 03:07 AM
10/16/13 03:07 AM
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Philadelphia
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radar Offline
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By the way that was not meant to snub the fella that described the t-slots as the 'intermediate circuit'. He is right it does flow fuel after the idle and before the mains.

It's just that it's also important to understand that the IFR and IAB combine to tune the T-slot mixture and the idle screws just meter that same mixture to the 'idle circuit'. That's why when you lean out the T-slot with a leaner emulsion you need to feed the motor more of it at idle with the idle screws.

I have only tuned a handful of DPs- it is possible that there are some with seperate intermediate circuits but I haven't read anything about them in my dusty holley books and I never tuned a dominator 2 or 3 circuit...

Re: How do you have your Holley Double Pumper tuned? [Re: radar] #1516160
10/16/13 10:05 AM
10/16/13 10:05 AM
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South Park, Pa.
68LAR Offline
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Quote:

By the way that was not meant to snub the fella that described the t-slots as the 'intermediate circuit'. He is right it does flow fuel after the idle and before the mains.




Understood. I didn't want to get "into the weeds", but just to somewhat clarify a little.


4 speed street legal. Best time 10.99 @ 124 mph on 93 octane pump gas @ 3926# total weight
Re: How do you have your Holley Double Pumper tuned? [Re: radar] #1516161
10/16/13 10:39 AM
10/16/13 10:39 AM
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Benton, IL.
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DaveRS23 Offline
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The reason I did not mention the slots in my earlier response was 2 fold. One reason was that I was trying to keep from writing a book on the subject and keep it simple enough for a beginner. Secondly, the question was about IFRs. And I wanted to explain why they were called Idle Fuel Restrictors.

I always try to explain that one of the biggest challenges with tuning carbs (in my opinion) is that all the part throttle circuits overlap. So when you do any one thing, it has multiple consequences. Just look at another thread here on Moparts where changing his idle circuit balanced his wide open ratio bank to bank. I am still trying to wrap my head around that one.

I know that the idle circuit still feeds fuel throughout the range, but I never suspected there was enough to affect the WOT ratio that much.

I still stand by my recommendation (based on experience) that if he gets his idle screws close to the 1 1/2 out area, his off idle will be much closer, too.

As with so many other things Mopar, tuning a race carb for the street is a collection of compromises. A good example of that is my own carb. I converted a 3 circuit Dominator to 2 circuits for my 500" street Wedge.

It cruises on the idle circuit, not the mains. And the cruise RPM likes a very different ratio than the idle does. So, I can have a solid idle or a clean cruise. But not both, apparently. Other than that issue, it is a rockin' carb.

Anyway, I know that I left out some details on my earlier post. But it was in the interest of simplicity and brevity. And I figured that if the OP got past this intro, we could get into the next part of tuning his DP.

AFTER he bought and read a book or two on Holleys.



Master, again and still
Re: How do you have your Holley Double Pumper tuned? [Re: DaveRS23] #1516162
10/16/13 02:12 PM
10/16/13 02:12 PM
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Philadelphia
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My first post on this thread was also more like a trail of bread crumbs than an instruction manual- went to the gym after work last nite and couldn't sleep so out came the novella!

There's still a lot of people on here willing to hand out hard won info for free moparts is awesome

Re: How do you have your Holley Double Pumper tuned? [Re: radar] #1516163
10/16/13 07:56 PM
10/16/13 07:56 PM
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Overpriced Housing Central
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You may be making carb adjustments to alter the symptom and not your root issue...

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