Fine tuning the reverse-idle 4160/4180 hybrid carb

[mrriggs]

I've mentioned my hybrid carb before. It's a
[List-6619-1] reverse idle 4160 Holley with a 4180 throttle body off a
[List-50003] truck carb. This was done so I could adjust the transfer slots with the reverse-idle [air] screws in the metering block, then fine tune the curb idle with the idle screws in the base plate.

I have been fiddling with it for some time and have found an fixed several other issues [weak ignition, timing, vacuum leaks] that were causing my "carb problems". I'd say it's about 90-95% of the way towards being flawless.

Current setup;
65 primary main jet
39 secondary metering plate
"Plain" vacuum secondary spring
Motorcraft CE-126 two-stage power valve
0.051" PVCR
Pink accelerator pump cam on #1
35 accelerator pump shooter
0.016" accelerator pump bleed
3-1/2 turns out air screws
2-1/3 turns out primary curb idle screws
1-1/2 turns out secondary curb idle screws

This is on a bone stock '84 5.0 HO engine.

It seems like 3-1/2 turns out on the reverse-idle air screws is pushing the limit of their usable range. The idle feed restrictions are buried inside the metering block and I'm not keen on dissecting it to get at them. This carb body has little holes drilled above the transfer slots. Would filling these holes allow me to close up the air bleeds a bit?

[Walking-Tall]

Yes, you should be able to turn the metering block air screws in some, if you (thin wall brass) sleeve the passages to block the small holes (or just block them with epoxy)... because just the same as taking the "race" (quite rich off-idle) out of a LIST-4412 500cfm Holley 2-barrel (same small holes in main body above transfer slots), blocking them makes them far more efficient running during transition/cruise/etc, those holes above the transfer slots make the slots function like longer than needed and than they physically are in the base plate... at very low throttle angles, the holes do act as air bleed like the tops of the transfer slots do, but after a certain amount of part throttle opening, the holes make the transfer slots act like they're too long... you'll probably end up also turning the base plate idle mixture screws in some too...



For reference, my documentation of every 6619 I've had my hands on had 0.028" primary idle feed restrictions... which when I de-reverse-idle them, is 0.002" too big for a mild or stock combination... but you're all adjustable, so no issue

[gr79]

i used 3M metal foil tape, several layers cut into small squares, to block the pv vac signal holes in the base of a carb body (pictured).
Very thin, sticky, and strong. So thin, even multi layers did not interfere with the throttle plate to body's gasket.
Reversible mod, as i did not know if i did the correct thing. Guess I did. Carb is working fine.
When i boost referenced the carb, modded a metering block channel to the pv.
The pv vac signal from under the carb, was not needed nor desired.
Blocked the holes in a quick safe way.
Nothing was needed to seal the pv cavity holes in the carb body that channeled to the base.

[mrriggs]

Thanks, Walking-Tall. The "virtual" transfer slots were probably way-way too long in this application since the 4180 base plate spaces the real transfer slots below the body. I was just afraid that those little holes were some how necessary for the reverse idle system to work properly.

We'll know for sure tomorrow. I was anxious to give it a try, didn't have any brass tube or 3M foil tape so I filled the holes with JB Weld after work today.

[mrriggs]

Definitely a HUGE difference! I took off for work this morning with no other changes but the plugged holes. It was struggling to idle and my mileage while cruising was down 6-10 MPG! Before leaving work I cranked in the primary curb idle screws to 1-1/2 turns out which fixed the idle and mileage.

I wanted to step down the jets since I have a 2-stage power valve. I pulled the metering block to drill the power valve restrictions to 0.051" only to find that they already are. Is that what these 6619-1 carbs normally have? I left them at that then screwed it back together with 61 jets. For the first time ever, it picked up a lean stumble when accelerating. Until now, it's always had a rich flat spot in the middle somewhere.

I put the accelerator pump shooter and cam back to the stock spec for the 6619-1 carb; orange cam on #1 and 0.031" shooters. An improvement but didn't totally cure it.

Played with the air screws and curb idle after most of these changes. A half turn of the air screws is all it takes to turn a slug into a snappy tire burner.

Current setup;
61 primary main jet
39 secondary metering plate
"Plain" vacuum secondary spring
Motorcraft CE-126 two-stage power valve
0.051" PVCR
Orange accelerator pump cam on #1
31 accelerator pump shooter
0.016" accelerator pump bleed
2 turns out air screws
1-3/4 turns out primary curb idle screws
1-1/2 turns out secondary curb idle screws

[Walking-Tall]

"... since the 4180 base plate spaces the real transfer slots below the body. I was just afraid that those little holes were some how necessary for the reverse idle system to work properly."
Yes, the 4180 bases have good (old school) size width and length primary transfer slots... the secondary slots, on the other hand, are astronomically long at about 0.345" as compared to good old school 0.180" length... so even though luckily a LIST-6619-1 has about the same size secondary idle air bleeds (0.044-0.046") as most 4180's, there should never, ever, EVER be any sort of secondary opening (lean) stumble even with the weakest secondary opening spring with that much secondary air:fuel transition! Those little holes in the main body above the primary transfer slots would have been more necessary with a reverse-idle LIST-6619-1 as is.

LIST-6619-1's commonly come with 0.046" power valve channel restrictions, like other common 600's, and #64 or #65 primary main jets. With 0.051" PVCR's, #62 primary main jets should be safe for WOT.

"... a slug into a snappy tire burner."
And that, folks, is how a dialed-in carburetor can hand EFI it's a$$ in all sorts of the most important departments. Good job

[mrriggs]

Hmmm... today it seems to be back to being pig rich and allergic to the accelerator pump. I'm afraid the stupid brass accelerator pump tube is leaking. I fought with this in the past and even special ordered square O-rings for it. Any time it comes apart it gets a new set of O-rings, lubed with RuGlyde, before going back together. I think it's time to ditch the stupid tube and convert it to use the standard metering block gasket.

[mrriggs]

Productive evening...





It was definitely wet in the power valve cavity. Power valve holds vacuum so it's not coming from there. Had to be those stupid o-rings.

[mrriggs]

Got it all back together tonight. Still has the same flat spot between 6-9"Hg that I've been fighting all along. I swear it's too rich; stumbles, slow to recover.

That is the point that the first stage of the two-stage power valve is open. I swapped it out for a 6.5 single-stage power valve and it made no difference.

It feels like the accelerator pump is drawn out too long. This is why I had a 35 pump shooter in it before. Kind of a robbing Peter to pay Paul approach since there isn't a lack of initial shot as is. What I need is less volume.

I switched back to the pink accelerator pump cam because it has a slower ramp. I, just now, looked at a chart of pump cam profiles and realize that I should have put it on position #2 instead of #1 to get less total volume. Anyway, with the pink cam on #1 it still has the same flat spot.

The float bowl has been modified with a replaceable bleed under the pump diaphragm. I popped off the bowl to screw in a larger bleed. When putting the diaphragm housing back on, one of the screws stripped out. Spent a couple hours fixing that. I don't have any 8-32 Heli-Coils so I drilled and [bottom] tapped the hole to 1/4"-28. Then drilled and tapped an 8-32 hole in the center of a 1/4"-28 bolt. Cut the tip of the bolt off, put a dab of Loctite on it and screwed it into the bowl. Ta-Da! Poor man's HeliCoil.

Unfotunately, all that effort didn't help. Still has the flat spot. I gave up for today.

Current setup;
61 primary main jet
39 secondary metering plate
"Plain" vacuum secondary spring
6.5 power valve
0.051" PVCR
Pink accelerator pump cam on #1
31 accelerator pump shooter
0.029" accelerator pump bleed
3-1/4 turns out air screws
2 turns out primary curb idle screws
1-1/2 turns out secondary curb idle screws

[mrriggs]

I spent most of the day swapping out accelerator pump cams and shooters. No matter what combination, it ALWAYS stumbles at 9"Hg when rolling on the throttle from cruise. There has to be something else going on here.

[85MUSTANGTGT]

How about trying a 9.5 power valve?

[mrriggs]

I don't have a 9.5 power valve but I do have a CE-130 two-stage power valve. The first stage opens at 11"Hg and has a larger orifice than the CE-126 that was in it before. I may try that just for the heck of it.

When I'm in 5th gear on the freeway I can hold it in the trouble area (6-9"Hg) and it runs smoothly. It's only an issue when rolling on the throttle.

[85MUSTANGTGT]

Worth a try, fairly easy change. Sure sounds like power valve to me though.

My car with both the stock engine and current stockish-cammed 347 seem to like a 9.5 power valve. That's also with 2 different carbs also, an 80670 and current 3310. Factory PV in both is a 6.5. Like you described, I'd roll through the throttle range hit about 9" and it would start laying down/coughing/stuttering, but push through that to about 6" where the PV opened and it would clear up and accelerate fine. The 9.5 PV filled that "hole".

[mrriggs]

Dang, I broke the CE-130 power valve. Snugged it down just a little too tight. Got the car all put back together with another power valve. After buttoning it up and leak checking it, I went and got the mail. There was a new CE-130 power valve in the mail box! How's that for timing? So I drained the bowl, again, and put in the new power valve.

I tested the old CE-130 (before breaking it) and the first stage opened at 11"Hg and the second stage at 5"Hg. The new CE-130 opens at 12"Hg and 6"Hg.

Compared to the CE-126 which opens at 10"Hg and 4"Hg. To know when each stage opens I stick the fuel side of the valve in my lips and blow while sucking on the vacuum side with a hand-held vacuum pump. The CE-126 is noticeably more restrictive than the CE-130 during the first stage so it's gotta have a smaller 1st-stage orifice.

Speaking of orifice... Since I broke a CE-130 in half I just kept breaking it until I got to the orifice in order to measure it. I was surprised to see only a single 0.021" hole. I always pictured it as two holes, I guess cause I'm used to seeing two PVCRs. Do the math on that, since you have one tiny hole feeding both jets, the first stage is equivalent to raising my 61 jets up to 63 jets. That's a pretty small jump considering the second stage is closer to 73 jets.

So how did it work. For the first time ever it's not stumbling at 9"Hg! No, now it's falling down somewhere between 10-11"Hg.

I'll pick up a 9.5, maybe 10.5, power valve and give it a shot.

[mrriggs]

We're having fun now! I made a tool to disassemble 2-stage power valves. Tried it out on a couple crusty old "22" power valves that came from '84 Mustang carbs. The orifice in them is 0.023". I got a Motorcraft CE-132 in the mail today and guess what number is stamped on it... "22".

Sweating bullets when I tried out the new tool on the CE-130, already broke one of those today. They have some crazy-strong Loctite holding the thin brass cage. It took a firm and steady effort to get it to slowly unscrew. I got it apart and drilled the orifice to 0.033" then drilled a second 0.033" hole on the other side of the plunger. That should be like stepping up to a 67 jet when the first stage opens. Half way between cruise and full enrichment.

Got it installed in the carb but it's too late for a test drive now so I won't know how it works until I leave for work tomorrow.

[mrriggs]

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.

[85MUSTANGTGT]

Making some progress sounds like. Hopefully Mike (Walking-Tall) will be along soon with some suggestions. Could try PM'ing him also. He sure has been a great help to me with my carb tuning endeavors.

I'm not the expert like Mike so just spit-balling, but wonder if 61 main jet is too small assuming that's what you're still using (from your post #9). Mike has some carb recipes floating around the forums, seems I remember a 65 was his preference for 600cfm carbs. Also, wonder if the flat spot you're seeing now could be a lean spot with secondary opening. Maybe try changing springs to see if flat spot occurs sooner or later depending on spring used. Not sure what RPM you're at when this happens. If still lower RPM, wouldn't be secondary related.

[mrriggs]

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.

[85MUSTANGTGT]

Hopefully Mike can get you an answer soon on the air bleed and emulsion circuits. Those are the two areas that are still a bit of a mystery to me.

I see and agree. If main jets are good at steady cruise then fuel needs to come from somewhere else, which would be power valve circuit. Thinking might still be worth trying a single-stage 9.5 or 10.5 PV if you can get a hold of one. Also wonder if going a bit bigger on PCVR's would help any.

What RPM range are you doing this test? Is it high enough to be on main circuit yet or low enough to still be in transition circuit? Mains coming in too late? Transition circuit running out of fuel?

[mrriggs]

I've been testing it at different speeds in different gears. The lower the gear, the more abrupt it seems to be.

I'm thinking now that it is the mains coming in late. Exercising my Google-fu, it appears that the "anti-siphon" bleeds in the angled passages that feed the boosters are largely responsible for the timing of the main circuit. On the agenda this evening is restricting these bleeds with wire to try and get it to kick off sooner.

[mrriggs]

The anti-siphon bleeds in this metering block are 0.028". I bent some 0.018" wire to stick on the holes with long tails so they can't go anywhere once it's put together. That basically cut the area of the bleeds in half. I also swapped back to the 6.5 power valve to make any differences more apparent.



There was an improvement but it was a long way from cured. I did the same thing with 0.028" wire to block them entirely. Again, there was a small improvement but the flat spot is still mostly there.

Current setup;
61 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

[Walking-Tall]

Productive evening...





It was definitely wet in the power valve cavity. Power valve holds vacuum so it's not coming from there. Had to be those stupid o-rings.

Nice work on the tube elimination. I just converted a "tube" metering block for regular duty today, with a short length (~0.310") of a brass transfer tube and jb-weld-ed in.

That can't be the original 6619-1 primary metering block. There are no regular "e-bleeds", but way up high in the "dog leg" bleeds and "emulsion" tubes (cup plugs up top of the idle wells, and flat top plugs up top of the main wells?), and I have yet to see any 600 vacuum secondary with straight leg boosters that have anti-siphon/kill bleeds like that into the angle passages to the boosters... they delay the main circuit starting up, increase the throttle angle necessity, and are really meant for use with the much stronger signal of down leg boosters. I'd be plugging those with small dabs of jb-weld... after "cleaning" the hole area countersinks with a hand-spun 1/16" and 1/8" drill bit... as well as the fact that you found 0.051" PVCR's already in there, and what I see in the picture above, they don't look like they've been drilled... back to reading further posts...

[Walking-Tall]

Side note about early carburetors, like most base LIST #'s, and/or the first no-dash and it's -1 or -2 iteration, that had "emulsion" tubes in the primary main wells, and some with and some without traditional "emulsion" bleeds: they always came with bigger primary main jets, like 4 #'s bigger than later iterations without the tubes in the main wells... because the presence of the tubes in the main wells represent pretty substantial restrictions in the well, requiring the extra fuel flow from larger jets...

[mrriggs]

That can't be the original 6619-1 primary metering block. There are no regular "e-bleeds", but way up high in the "dog leg" bleeds and "emulsion" tubes (cup plugs up top of the idle wells, and flat top plugs up top of the main wells?), and I have yet to see any 600 vacuum secondary with straight leg boosters that have anti-siphon/kill bleeds like that into the angle passages to the boosters... they delay the main circuit starting up, increase the throttle angle necessity, and are really meant for use with the much stronger signal of down leg boosters. I'd be plugging those with small dabs of jb-weld... after "cleaning" the hole area countersinks with a hand-spun 1/16" and 1/8" drill bit... as well as the fact that you found 0.051" PVCR's already in there, and what I see in the picture above, they don't look like they've been drilled... back to reading further posts...

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

[Walking-Tall]

Dang, I broke the CE-130 power valve. Snugged it down just a little too tight. Got the car all put back together with another power valve. After buttoning it up and leak checking it, I went and got the mail. There was a new CE-130 power valve in the mail box! How's that for timing? So I drained the bowl, again, and put in the new power valve.

I tested the old CE-130 (before breaking it) and the first stage opened at 11"Hg and the second stage at 5"Hg. The new CE-130 opens at 12"Hg and 6"Hg.

Compared to the CE-126 which opens at 10"Hg and 4"Hg. To know when each stage opens I stick the fuel side of the valve in my lips and blow while sucking on the vacuum side with a hand-held vacuum pump. The CE-126 is noticeably more restrictive than the CE-130 during the first stage so it's gotta have a smaller 1st-stage orifice.

Speaking of orifice... Since I broke a CE-130 in half I just kept breaking it until I got to the orifice in order to measure it. I was surprised to see only a single 0.021" hole. I always pictured it as two holes, I guess cause I'm used to seeing two PVCRs. Do the math on that, since you have one tiny hole feeding both jets, the first stage is equivalent to raising my 61 jets up to 63 jets. That's a pretty small jump considering the second stage is closer to 73 jets.

So how did it work. For the first time ever it's not stumbling at 9"Hg! No, now it's falling down somewhere between 10-11"Hg.

I'll pick up a 9.5, maybe 10.5, power valve and give it a shot.

I've never been a fan of two-stage power valves, and your findings of a single 0.021" feed hole tells me why... basically doing nothing, at whatever vacuum/load level, definitely a sizable restriction to the PVCR's, when it's the full augmentation of the PVCR's are needed at those load levels... and I'm sure between that fact, the potential unknown of whether bleeds in the e-tubes are clean and clear open, the kill bleeds, and the #61 jets, are at least where the problem is... after all, the great majority of all driving, including cruise, and quite up the throttle opening angle of part throttle acceleration, are handled by the primary idle/transition circuits... all depends when the mains start up... and if main circuit boosters are late to the party due to kill bleeds, and nano-seconds later through continued acceleration the full augmentation of the PVCR's are required due to the load on the engine...