Fine tuning the reverse-idle 4160/4180 hybrid carb

[mrriggs]

In the book Super Tuning and Modifying Holley Carburetors by Dave Emanuel it has a step-by-step rebuild of a 6619-1 with a metering block identical to mine.

[Walking-Tall]

The modified 2-stage power valve definitely made a difference. The flat spot is not as consistent as it was before. Rolling on the throttle in second gear is the same as before but in third gear it only has a tiny hole between 5-7"Hg. Still seems like I'm trying to Band-Aid over the real issue.

I'm sure Walking-Tall could elaborate more on this. From what I've gathered, inside this metering block there are brass "emulsion" tubes with a bunch of holes below the fuel level. The purpose of this is to increase high end fuel flow to the boosters through smaller main jets. The downside is that it delays the main circuit start-up which would explain the transfer slot extender holes in the main body. The holes that I compromised by swapping to a thicker throttle body... then filled in with JB Weld.

If this is correct then the solution would be to either extend my transfer slots or eliminate the excess emulsion holes to get the main circuit flowing sooner.

The purpose of "emulsion" bleeds (I prefer 'booster air correction bleeds') in either case, with single up-high bleeds and tubes, or with traditional "emulsion" bleeds... are a perfect part of the original design that work in conjunction with the main air bleeds, to counter a booster in a venturi's tendency to exponentially flow more air:fuel than is necessary for a flat air:fuel ratio (ie. 12.5:1 air:fuel ratio for WOT) from the point you put your foot down and the mains/booster start doing the fueling, up to whatever the maximum rpm of the engine is... and when correctly calibrated, that's exactly how the good old ones work... a flat air:fuel ratio that is load dependent, not rpm dependent, and neither any kind of "fuel curve" (usually blobbing rich to begin with, and then veer lean up the rpm scale... the most potentially dangerous situation for a fully loaded engine and revving up to it's upper limits) that all the new-and-improved models provide...

[Walking-Tall]

Thanks for the feedback, Thomas. Spit-balling is much appreciated. If we bounce around ideas long enough we're bound to nail it sooner or later.

The airbleed/emulsion circuits on this carb are not typical of other 600cfm carbs. I did PM Mike about what it would take to make them more traditional so there is a solid baseline to work from. I'm sure he's a busy dude. I can wait.

Until two weeks ago, the secondaries were tied shut. Enabling them made no difference to the flat spot. The secondaries are opening pretty late with the "plain" spring. I'm not going to mess with that until I get the primaries figured out.

Bigger jets or quicker power valve will likely fix that one issue but I'm reluctant to do so because the "steady-state" tune does not warrant it. When cruising at light load or holding it at 8"Hg, I am not experiencing any lean surge that would indicate that it needs bigger jets. So by fixing the one issue, I'd be creating another issue, poor gas mileage.

This spring's rush is proving quite busy. I'm juggling five carburetor builds all at once at the moment!

Poor gas mileage rarely has much to do with (reasonably) bigger main jets, unless the car's got 2.26:1 rear gears, 30" tall rear tires, and you're in overdrive, and your foot needs to be deep into the throttle enough to actually be running on the mains, or worse yet also the PVCR's...

Do you know what size the primary main air bleeds are? I've seen variations between 0.025-0.028" with or without e-tubes, all with 0.046" PVCR's, and all originally with #642 primary main jets... where some juggled compromise also goes on with secondary main air bleed size...

[Walking-Tall]

On the top of the metering block it has "L6619" with "7492" under it on the left side and "7204" on the right.

I've seen a number of screw-ups... and a block incorrectly stamped isn't above Holley's infinite wisdom, lol...

Hopefully there actually are tubes with e-bleeds in the main wells, because in combination with booster kill bleeds, the ones up high in the dog legs would most innocently act as vapor vents, but worse also probably act also as delay, and then allow the boosters to feed veering rich with rpm. Flat top caps on top of the main wells? Can you see brass in through the up high bleeds?

[mrriggs]

Do you know what size the primary main air bleeds are?

Just ran out and measured them, 0.026".

[Walking-Tall]

In the book Super Tuning and Modifying Holley Carburetors by Dave Emanuel it has a step-by-step rebuild of a 6619-1 with a metering block identical to mine.

I see that in the book here too. I dunno what to tell ya, I haven't met one like it. It's possible the kill bleeds etc in the book block and like yours were to work with and coincide with certain size (smaller) primary idle air bleeds and a differing flow area (bigger main body holes than others, wider/longer slots than others...? No idea...) of the virtual primary transfer slots...

[Walking-Tall]

Just ran out and measured them, 0.026".

Okay, makes sense with a metering block with tubes (smaller main air bleed, ultimately richer acting main jet), because Holley's "Numerical Listing" shows one single 6619-1 and a single listed primary main jet size of #642, otherwise known as a close-limit #64 main jet. The only variations of 6619-1's are no other dash numbers, but earlier/later date codes, which is probably the variations I've seen...

[Walking-Tall]

If I were you, a new 600 metering block from AllState Carburetor ($30 US + shipping) is what I'd do. You get 0.046" PVCR's and 0.026" down-low visible idle feed restrictions and no kill bleeds... block with jb-weld the up high bleeds into the main wells (image will be below) because they are unnecessary where there are no e-tubes... then drill the regular idle ~0.062" idle mixture screw (your "air screws") tip passages out to what your reverse-idle passage holes are... if memory serves, reverse-idle mixture screw tip passages are ~0.100"... measure yours and duplicate...



Link to new inexpensive (choice of gold or silver) block: https://allcarbs.com/product/holley-...block-600-cfm/


Last time I got one I got the classic gold version, which went into a 700 double pumper, so I drilled the PVCR's to 0.053" and installed adjustable 0.031" idle feed restrictions due to the stock/mild combination that the carburetor went onto. Here shows the blocked unnecessary up high bleeds into main wells:




Just watch out for (and remedy) any Holley F-up's like below...

This side, fine:


This side, not so much, LOL! Oops, upper angle passage never drilled... needed drilled to connect with the idle well:



Then there are no unknowns buried in idle or main wells, that may or may not be clean and clear and also maybe causing issues, etc... then put some #64 or #65 primary main jets and whichever vacuum/load level power valve your combination requires for the beginning of full jets+PVCR enrichment, and she ought to make more sense and behave better... keep us posted...

[mrriggs]

Thanks for jumping in here, Mike. I didn't realize it was that easy to modify a standard block for the air screws.

Grabbed an 80457-2 off the shelf that came from a parts car. Found this inside the bowl...



Uh, yeah... NEXT!

Pulled the metering block off an 1850-3 parts carb instead. BINGO! It's got all the standard e-bleeds.

[mrriggs]

Had an interesting discovery today. Turns out I was too hasty in dismissing the effectiveness of blocking the anti-siphon bleeds. I just shoved the wires in there, took a quick spin around the block and called it a flop.

Well... driving to work this morning I realized that it was now stupid-lean when cruising. On the drive home, I cranked in the air screws to richen up the transfer slots which cured the cruise mixture but also made it fat and blubbery on tip-in. When I got home, I slapped in some 65 jets then put the air screws back where they were. It is now running better than ever!

So what's going on here? If you're cruising on the transfer slots then why are changes to the main circuit affecting it? I think the answer lies in the fact that the idle/transfer circuits are not fed fuel directly from the float bowl but rather from the main wells. When you are cruising there is air moving through the venturis which causes a pressure drop in the boosters. The pressure drop isn't great enough yet to pull fuel up and out of the wells but they are still presenting a low pressure to the wells.

The anti-siphon bleeds add a bit of high [atmospheric] pressure to the tops of the wells which counters the low pressure from the boosters. When I blocked the anti-siphon bleeds it lowered the well pressure while cruising which means less pressure feeding the transfer circuit so it ran leaner. Idle and tip-in mixture remained exactly the same after blocking the anti-siphon bleeds [and after bumping up the jets] because the tiny amount of air going through the veturis at idle creates no pressure drop so the main wells see only atmospheric pressure.

Current setup;
65 primary main jet
39 secondary metering plate
"Plain" vacuum secondary spring
6.5 power valve
0.051" PVCR
Pink accelerator pump cam on #1
35 accelerator pump shooter
0.016" accelerator pump bleed
0.000" anti-siphon bleeds
3-1/4 turns out air screws
1-3/4 turns out primary curb idle screws
1-1/2 turns out secondary curb idle screws

[85MUSTANGTGT]

Glad to hear you're having some success.

I need to spend some time reading Mike's post and try to retain some of it.

[mrriggs]

Still tweaking and massaging this thing. Making little changes then driving for a bit to get a feel for it. Stepped down to a little smaller main jet and went back to the [unmodified] CE-130 two-stage power valve. Also drilled out the primary idle air bleeds from 0.045" to 0.052" to get the air screws in a bit.

Current setup;
63 primary main jet
39 secondary metering plate
"Plain" vacuum secondary spring
Motorcraft CE-130 two-stage power valve
0.051" PVCR
Pink accelerator pump cam on #1
35 accelerator pump shooter
0.016" accelerator pump bleed
0.000" anti-siphon bleeds
0.052" primary idle air bleeds
2-1/2 turns out air screws
2 turns out primary curb idle screws
1-1/2 turns out secondary curb idle screws

[Walking-Tall]

Still tweaking and massaging this thing. Making little changes then driving for a bit to get a feel for it. Stepped down to a little smaller main jet and went back to the [unmodified] CE-130 two-stage power valve. Also drilled out the primary idle air bleeds from 0.045" to 0.052" to get the air screws in a bit.

Current setup;
63 primary main jet
39 secondary metering plate
"Plain" vacuum secondary spring
Motorcraft CE-130 two-stage power valve
0.051" PVCR
Pink accelerator pump cam on #1
35 accelerator pump shooter
0.016" accelerator pump bleed
0.000" anti-siphon bleeds
0.052" primary idle air bleeds
2-1/2 turns out air screws
2 turns out primary curb idle screws
1-1/2 turns out secondary curb idle screws

.............

[mrriggs]

I went up a step on the main jets, put the modified CE-130 power valve in it, and closed up the primary curb idle screws a bit. It's running NICE! Crisp throttle response, strong acceleration, smooth everywhere AND I've picked up 2-3 mpg.

Current setup;
64 primary main jet
39 secondary metering plate
"Plain" vacuum secondary spring
Modified two-stage power valve
0.051" PVCR
Pink accelerator pump cam on #1
35 accelerator pump shooter
0.016" accelerator pump bleed
0.000" anti-siphon bleeds
0.052" primary idle air bleeds
2-1/2 turns out air screws
1-1/2 turns out primary curb idle screws
1-1/2 turns out secondary curb idle screws

[Walking-Tall]

Excellent! If we keep this sorta stuff up, we'll subvert a lot of the (mis)information on the internet, LOL