Idle Transfer Slot on secondaries?

[tjpatte]

I don’t see any restrictors in the main body do you?

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.

 

[340inabbody]

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?

 

[Bewy]

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.

 

[Bewy]

And...

 

[Bewy]

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

 

[Hysteric]

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.

The standard Holley metering blocks come with the IFR in the right location.

No Sir, not sure if any carbs actually come with them,

They do. I just pulled some out of a 650 HP main body as I paired it with a stock Holley base plate.

 

[Hysteric]

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?

Yes.

Are all 4150 metering blocks the same?

Pretty much.

Do they sell metering blocks with the lower T-Slot restrictor set up?

Yes, Allstate Carbs

Also what is the reason to use the Holley base plate on the Proform? Is it because of the linkages?

Depends on the Tslot size.

 

[340inabbody]

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.

 

[340inabbody]

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.

 

[Bewy]

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.

 

[340inabbody]

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.

Thanks Bewy what are you suggesting I should do about my PCV? It’s set up as stock.