Idle Transfer Slot on secondaries?

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340inabbody said:
I don’t see any restrictors in the main body do you?
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No Sir, not sure if any carbs actually come with them, think they just drill them to a predetermined size.

If I were you, I would just start with squaring the primary Tslot and close the secondary until your idle lowers. After you get there see where you’re at.

I think you’re idle is too high right now. Listening to your engine I have a rougher cam, 251/258 at 50, and I can bring my idle down to 750 if I want. I use 900 to keep the cam lubed at idle.
 
Ok the link with explanation is good and I understand it. This modification moves the IFR to below the fuel line making idle smoother for a lower vacuum system because it is submerged and less affected by air pressure?
I see this modification can be done on both carbs as a typical modification by many people. Saw a video on this as well.

I assume if I mess it up I can get a replacement metering block worst car right? Are all 4150 metering blocks the same? Do they sell metering blocks with the lower T-Slot restrictor set up?

Also what is the reason to use the Holley base plate on the Proform? Is it because of the linkages?
 
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Holleys came with FIXED air bleeds for DECADES....& people like me were tuning them just fine....
You have started in the WRONG place with this. You get the idle timing dialled in, THEN work on the carb. With 11" of vac, it wouldn't surprise me the engine needs 35-40* at idle. The extra idle timing will increase idle rpm, allowing the t/blades to be closed more at idle & THEN the mixture screws will hopefully work in adjusting idle quality. If not, blades may still be too high, exposing too much T slot. The fix for that is bypass air; one method is drilling holes in the t/blades. Some TQs & AVS production carbs reqd bypass air, which was obtained by holes in the plates or body.....or both.
First step is to increase timing at idle, in gear, until the highest rpm is reached. That is what the engine needs for best efficiency/smoothest idle. I suggest you do this & report back.
The reason T slots were added to the secondaries was to bleed a small amount of fuel out of the bowl so that there was always fresh fuel in the bowl.

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And this guy picked up 2" of vac by giving the engine the idle timing it wanted.....

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tjpatte said:
Do this to both carbs regardless of which one you wish to use. This will calm down your idle circuit and make tuning exponentially easier.
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The standard Holley metering blocks come with the IFR in the right location.
tjpatte said:
No Sir, not sure if any carbs actually come with them,
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They do. I just pulled some out of a 650 HP main body as I paired it with a stock Holley base plate.
 
340inabbody said:
Ok the link with explanation is good and I understand it. This modification moves the IFR to below the fuel line making idle smoother for a lower vacuum system because it is submerged and less affected by air pressure?
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Yes.
340inabbody said:
Are all 4150 metering blocks the same?
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Pretty much.
340inabbody said:
Do they sell metering blocks with the lower T-Slot restrictor set up?
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Yes, Allstate Carbs

340inabbody said:
Also what is the reason to use the Holley base plate on the Proform? Is it because of the linkages?
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Depends on the Tslot size.
 
Bewy, I hear and have seen how A significant Advance like 43° at idle can smooth out the idle. But if the mixture is off due to lack of airflow because of the throttle plate exposing to much of the T-Slot then it seems to me (not claiming to be an expert here) the added advance to compensate is not the right approach. It masks the fundamental problem of a bad mix.

Seems like tuning is an iterative process going back and forth from carb adjustments to timing tweaks.

I did buy the Progression Distributor so I will easily be able to modify the curve at will and on the fly. But I need to have a tuned carb that isn’t way off like I feel it is right now.

Does this make sense? I am trying to learn here and this thread has been excellent for me.
 
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By the way here is a sample of one of my distributor curves. I haven’t played much around with it yet because of large idle drop going into gear and fouled plugs.

IMG_3426.png
 
340,
It is all about the tuning sequence. With a project liker yours, you do the idle timing FIRST, because all the other adjustments flow from this. Forget about the carb for now. As long as the engine will idle [ well enough ], do the ign test in post #53.
A 440 I set up, had similar idle vac to your engine, reqd 42-44* at idle. It was a turd with the factory 10-12* BTDC.
Also, you need to check the PCV if you are using one. It may be pulsating with the low vac, changing the amount of air been ingested at idle, causing havoc with idle adjustment.
 
Bewy said:
340,
It is all about the tuning sequence. With a project liker yours, you do the idle timing FIRST, because all the other adjustments flow from this. Forget about the carb for now. As long as the engine will idle [ well enough ], do the ign test in post #53.
A 440 I set up, had similar idle vac to your engine, reqd 42-44* at idle. It was a turd with the factory 10-12* BTDC.
Also, you need to check the PCV if you are using one. It may be pulsating with the low vac, changing the amount of air been ingested at idle, causing havoc with idle adjustment.
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Thanks Bewy what are you suggesting I should do about my PCV? It’s set up as stock.
 
PCV. Once you have the idle timing correct, adjust idle mixture as best you can.
With the engine idling, in gear, remove the PCV [ it will probably be in the valve cover ]. If it is rattling, it is not working; there is not enough vacuum to overcome the internal spring.
If the pintle is not moving, gently push on it with a small screwdriver. If the pintle moves, it is not fully seated, which is also bad, because the pintle has a tapered seat, so the air being drawn past it idle will vary & make it hard to get a consistent idle.

Bottom line: PCV pintle needs to be pulled in with no movement at idle.

Fix for low vac there is an expensive Wagner adj PCV....or what I have been doing for many years: get a 3/8" bolt, & cut off about 5/16-3/8" length; drill a 1/8" hole through it. Push this into the PCV hose. Job done.
 
Or you could put an 800 AVS2 on it and be did wif all dat, yo. lol
 
Bewy said:
PCV. Once you have the idle timing correct, adjust idle mixture as best you can.
With the engine idling, in gear, remove the PCV [ it will probably be in the valve cover ]. If it is rattling, it is not working; there is not enough vacuum to overcome the internal spring.
If the pintle is not moving, gently push on it with a small screwdriver. If the pintle moves, it is not fully seated, which is also bad, because the pintle has a tapered seat, so the air being drawn past it idle will vary & make it hard to get a consistent idle.

Bottom line: PCV pintle needs to be pulled in with no movement at idle.

Fix for low vac there is an expensive Wagner adj PCV....or what I have been doing for many years: get a 3/8" bolt, & cut off about 5/16-3/8" length; drill a 1/8" hole through it. Push this into the PCV hose. Job done.
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I have made my own 4 cylinder/carburator manometer using welding tips I see what your trying to accomplish with making a restricter to smooth out a potential problem from the PVC.
Not sure I need to worry about the PCV as I am having more basic issues like the fuel mixture screw not being effective. That’s a carburetor issue from what has been explained here. The solution is tuning the carburetor. If the PCV however is causing bounce which I certainly am having can’t I simply disconnect temporarily from the carb and plug it and move on dealing with the tune? If the bounce stops that will also tell me that indeed the PCV is causing that.

Remember I do have a somewhat reasonable distributor curve one that I should be able to tune the idle circuit with. Its no 48° at idle but it is 28°.
 
I am about to put my carburetor back on and then was wondering. Is it possible that I have clogged pilot air or fuel passages? Is there an easy way to test this? I do have an ultrasonic cleaner maybe tossing the blocks in there before I put it back on a good idea? The pilot jets on my motorcycles get clogged as often as Biden says “folks”….
 
You can run without PCV. But these carbs are designed to pull about 3 cfm of the ~20cfm of idle air from the PCV. Without PCV, the air has to come from somewhere else...such as small holes in the t/plates.

I no nothing about Progression Ign Dist......but if it does not allow you give the ign timing at idle that the engine wants, then that is not Progression....that is going backwards.
Sometimes the simple ways are the best ways......like a std dist with adj vac adv; also very reliable.
 
FWIW, I used a feeler gauge between the idle stop lever for the secondaries to experiment with the idle speed screw of the primaries. It works, no holes required.
 
DON BURKHOLDER said:
FWIW, I used a feeler gauge between the idle stop lever for the secondaries to experiment with the idle speed screw of the primaries. It works, no holes required.
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It dies and if you noticed like me it’s VERY SENSITIVE! Small fractional turns moved idle a lot!
 
Nice. This wasn't around in the seventies. I eventually used a finishing nail to create a screwdriver by grinding a flat blade on both ends, phased 90 degrees apart Then I bent it in a "Z" shape to reach up in the screw hole with the carb installed. If you can't engage the slot of the screw, flip it over. Yes, it doesn't take much of a turn. Then go back to the primary idle screw and back it off.. Had a cammed 68 340 Barracuda S with 3.5 inches of vacuum in gear at idle that would burn your eyes out because the power valve opened at 6.5 inches on the Holley 650 double pumper
After a power valve change, a secondary idle stop adjustment, an MSD 6 and with Roads Lifters, I could idle down to 700 RPM..
 
DON BURKHOLDER said:
Nice. This wasn't around in the seventies. I eventually used a finishing nail to create a screwdriver by grinding a flat blade on both ends, phased 90 degrees apart Then I bent it in a "Z" shape to reach up in the screw hole with the carb installed. If you can't engage the slot of the screw, flip it over. Yes, it doesn't take much of a turn. Then go back to the primary idle screw and back it off.. Had a cammed 68 340 Barracuda S with 3.5 inches of vacuum in gear at idle that would burn your eyes out because the power valve opened at 6.5 inches on the Holley 650 double pumper
After a power valve change, a secondary idle stop adjustment, an MSD 6 and with Roads Lifters, I could idle down to 700 RPM..
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@RustyRatRod
 
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