Where is IFR in this metering block

It's a 6361 metering block. I believe its in the idle well, maybe cast in or a pressed in restrictor. How hard to modify or replace ? thanks

The dimples in the slots on either side of the PV plug do not show the idle feeds drilled. Is that the secondary block?

Yeah, that's what is puzzling. It's the primary. Carb is 4668.

Are the 4 brass plugs at the top all “cups”, or are the inner two “flat”?

If they’re flat like in the pic I posted, those are likely “idle tubes”, like what are used in 3 circuit 4500 carbs.

If they’re cups, I’d just pull one out and see how the main well is configured.
Replacement plugs are readily available.

The “If it were me” answer is........ if I wanted to hit the easy button to do some experimenting, I’d just buy one of these and see what happened:
https://www.holley.com/products/fue...metering_blocks_and_plates/parts/134-155

I might have another one I could sacrifice if I want to open it up.

That's an early 70s emmisions carb.
Lot's of things were done different and very specific for the application.
If you have the whole setup, and are running close to stock, you can prob do some minor tweaks to increase the range of adjustment.
That stuff was all set up for fine adjustment of relatively lean idle (14.2:1) and high idle rpm.
Shop manual and theMTSCs cover most of those changes.

If you want it to be more like a normal pre-emissions carb. Take a look at what Mike did here.
https://www.tapatalk.com/groups/racingfuelsystems/list-4668-t1344.html

Take note of the booster notch and other staggered restrictions Mike found - that's specific to work with the intake manifold for best distribution.

Might be an option. Does this have replaceable idle jets ?
The metering block in question is off the 383 stocker engine

Thanks for that link !

If you want it to be more like a normal pre-emissions carb. Take a look at what Mike did here.
https://www.tapatalk.com/groups/racingfuelsystems/list-4668-t1344.html

Well well........ that is an odd duck.
It doesn’t look like the idle well is drilled at all....... at least, not from the top.

IMO, anything “oddly” done(compared to “normal” performance metering blocks), was to address something emissions related.

For what you’re doing........ I’d def be experimenting with a more traditional and user friendly metering block.

Edit:
There’s a lot of good info in that link Mattax posted.

However........ I don’t see how all those mods would put you further ahead than just using a more tradition block.

I see in the specs for the original block that the ifr in the idle tube was .022”.
That’s not going to work at all in a Stocker build.

I’d also be very careful examining both the primary and secondary idle feed circuits, since there was a mention in the link of the primary idle curcuit interacting with the secondary side.
I would insure those were isolated from each other.

It has to be done as a package with the main body. A lot of work.
When I was looking at the late 69-70 predecessors to the 4668, the transfer slot circuit was seperated from the idle circuit.
Transfer slot got its own air bleed in the main body and IIRC fixed restriction.
The idle circuit has an adjustable but hidden restriction after the air bleed. The air bleed in those cases was externally adjustable.
IMO its best to use that carb for its original use, with relatively minor mods if there's no reason/desire to keep the emissions characteristics. I'm not suggesting emissions control is always bad, but some of those early setups were tradeoffs for fuel economy and even sometimes NOx in favor less HC and CO. I wouldn't blame anyone who wanted to run a richer stronger idle at lower rpm and a more normal initial timing to go with it.

I don't have a '71 service manual, but that's probably the one with the details of this carb's secrets

Did you see there is also an older thread where Hank is working on a 4668
https://www.tapatalk.com/groups/racingfuelsystems/viewtopic.php?p=12160#p12160

Thanks for the info guys. Mattax, this is a stock eliminator race engine.

I've done a fair amount of working on this carb and it's functioning "OK" but could use quite a bit of fine tuning. As far as the IFR goes, the engine idles decent, but has wanted to die when put in gear. So I'm pretty sure it's lean. The idle rpm is pretty hign, 1300ish. I wonder if I could simply reduce IAB and have the idle mixture screws a little further out ?

The OP is running the carb on an NHRA stock eliminator car.
The factory low speed calibration is totally out to lunch for that application.

The rules dictate the correct carb has to be used, and that fuel metering mods are legal(but not the addition of 4 corner idle).

Like I said previously......if I were doing it, it would get a set of new std performance style metering blocks, and then I’d do the same types of mods to the main body/baseplate that were done in that link.

There is no need to try and work on “part throttle cruise” in this application.
It needs to start well, idle decent in gear, do a burnout okay, and have decent manners when staging........along with providing a good fuel curve at WOT.

I’m pretty sure the main issues the OP is having are related to how the motor runs when in other than WOT operation.
Which after seeing how they’re calibrated...... makes perfect sense.

After looking thru those two threads....... for even modest performance use...... it appears the low speed circuits on those carbs are a mess.

I need to better understand the circuit before suggesting anything permanent.
It looks like the IFR is in the bottom of the tube and from what you're saying the IAB's are in the normal location.
Are the idle mix screws in the standard location etc?
A relatively easy experiment would be to stick some wire in the IABs.

Are you using the Direct Connection 'Tach Drive' distributor?
Could be losing timing with rpm if idling at 1300 with any distributor, but the race distributors its a little worse.

I just took a quick look at a '71 Plymouth FSM.
A couple questions I have now is
1. how the hot idle compensator works. The text says this opens an air bleed, but does say how.
2. Is there a second air bleed for the transfer slot or not. Description says there is one but I'm not seeing it or a third circuit. Of course the text is covering 4 different 4160 carbs...


As far as the idle mix screw goes, take one out and see if it has a needle valve tip or looks like the ones Mike found.
My guess is that the flat tip worked to increase the effect of restriction within the 270 degrees it was originally limited to.
I'd take a note of how the flat runs, and also be very gentle when closing it to the bottom. It probably doesn't shut off flow completely like a needle tip would. Not that you need to shut off the flow, but when experimenting its common to run the screws in until engine slows.

The IAB and mixture screws are in the normal locations. not sure about the transfer bleed. timing is locked out at 37

The hot idle compensation is a curved piece of sheetmetal the bends as it get hot and opens an air bleed to dump below baseplate. I've plugged it.

unplug that hot idle compensation and let it suck air,jet up as needed and your car will go faster.
but fix your problem first or you will have more trouble

Thanks. So the compensator is not a bleed in the traditional sense (into the circuit) but more like a variable on the PCV or bypass air.

I think if there is a second transfer bleed it will be visible near the regular IAB's, and seperate path to the transfer slot. That would be visible on the body facing the metering block.
37* locked out is, IMO going to make it more difficult to get the idle producing more power. I'm sure that's very close to what is needed at WOT during the run.
But whether that much is really needed at idle I don't know. A richer fuel mixture at idle will be stronger but will also burn quicker.

When you say IFR are you wanting the idle fuel feed restrictors or intermediate, transition, fuel feed restrictors?

Cab, I'm looking to richen the idle. I think richening the transition portion is probably needed, although I'm not sure how to evaluate that. I have a WB, but I doubt I can pull any intelligent data from that. If I can improve the idle quality, so it seems cleaner, chrisper, and the rpms don't drop excessibly when I put it into gear, that'll be great. If nothing changes, it's good enough to race it now. I'll experiment with the bleeds and see if it improves things.

I don't know if you should or shouldnt open the hot air bypass. But, if you need to reduce the throttle position, then the hot air compensator can be opened and used as a bypass. It will be like an 'idle-eze' setup in a different location.

As far as experimenting, measure some wire, measure the idle air bleeds with a pin gage or drill bit shank. Then stick the wire in each idle air bleed and see what happens. Write everything down.
The easy way to retain the wires is run them up over the choke tower (assuming its still there), then under the aircleaner gasket. I actually prefer to use one wire for both bleeds. It takes a little more time to bend and fit.

Opening the hot idle comp is a great idea for WOT, but would hurt me with trying to richen the idle. I'll have to save that idea for later. I'll update this after I do some adjusting.

is this a factory mopar holley? if so the idle jet is probably a tube in the main well and can be seen by removing the jets. and, if i'm correct they are very lean and reducing the idle air bleed helps.

Yes it is. thanks I'll have a look.

So I've tried tried putting wire in the idle bleeds. The original bleed size is .066" I used .014, .018, .030 wires. I gained about 50 rpm in gear, but did not really see much of a change. Vacuum is around 12 in. idleing. Mixture screws were 1.5-2 turns. Throttle plates all are drilled .120 and transfer slot closed up nicely, open about .030" I may try putting the timing at 20, 25 to see if it helps. Locked at 37 now.

It is. We can see it in the photos in the linked threads. There's a photo with the jets removed.

50 rpm less drop in rpm is progress.
.066 IAB = .00342 in sq
.030 wire = .00071 in sq
Equivalent of .059 IAB
You could try larger.
.035 wire would be equivalent of .056

However it is looking like what will be needed is larger IFRs.
I think the engine will like a little less timing at idle, but very well may need even larger IFRs then.
I've not removed the tubes from blocks, but several guys on RFS have. Besides Tuner, Deeproots, Hank, Mike all have with varying luck in not damaging them in the process. So its definately possible. I can try to put you in touch with one of them if you want. Mark who posted earlier in this thread, and Dom (Thumperdart) may have experience removing them also.

if you're allowed to change metering blocks, that might be the easiest solution, assuming all of the circuit connections line up.

the relationship between the idle jet (tube in the well) and the idle air bleed are screwed up on those mopar holleys. I always do the idle jet half the diameter of the air bleed, the old way was to just reduce the air bleed size. this was done by tamping a piece of #4 lead shot into the air bleed hole and drilling the lead. in this case the air bleed would end up at .044". I've done this before but really believe you need to go after this in both directions. reducing the air bleed gives a stronger signal to the idle circuit but those small jets will only flow so much fuel. the last one I did for a six pak I drilled out the idle jet to .028" (was .0023") and reduced the air bleed to .056" with the lead shot. those brass tubes won't allow a proper diameter jet but area wise small changes can make big differences in area. the hard part is going thru the bottom of the metering block to get to the idle jet and deciding how to plug the hole up. I used 6-32 set screws thinking I may want to get back in there to clean a jet up. I was afraid of removing the idle jet from the metering block and damaging them and not being able replace them. quick fuel makes a universal metering block that might be easier if nhra tech allows it.

Great info. I like the idea of going thru the bottom of the metering block. I will give it a shot. I could probably just change the metering block, but modifying the original will be much more fun

I would check and see if they will allow a replacement cast block be used, a Holley 11180 block will allow you to put adjustable lower idle feeds in.

i was looking on line sometime back and found some aluminum plugs for carb holes, believe it was Mikes Carbs, if you don't want to do the set screws. set screws will need to be sealed. I've found that playing with the air bleeds can help some but in the end it's fuel volume you need and the only way to increase it is bigger idle jets. I really go after idle jets anymore for lower rpm.

Unless the rules have changed, you aren’t allowed to drill the secondary blades.

I also don’t recommend “asking” if you could use different metering blocks.

i haven't messed with one of those carbs in 50yrs but I do remember not getting it to work properly. I lot of that was lack of knowledge when I was 22yrs old. this is off topic but I remember having real fuel control issues with those fixed needle and seats. I think they are something like .075" seats and they didn't like pressure. if you keep in mind that those engines came with 3-5psi fuel pumps and most of those pumps wouldn't do 5psi you can see were a problem could arise with a 6-8psi pump which is what I used back in the day. I don't know if there's a way to get creative here but I doubt that .075" seat can provide enough volume without overpowering it with pressure. the carb i played with had a small brass balance tube between the primary and secondary bowls. that brass tube may be necessary for the fixed needle and seats but might become an issue if you do get creative with different needle and seats.

Actually I don't understand how this would help at WOT. It's just a small air passage. Yes?
At idle, consuming 4 to 6 cfm, or maybe 8-10 with a high idle rpm, the compensator will flow a small but noticible percentage of that.
At mid to high rpm, WOT, its going to be a tiny fraction of a percent.
(It's not like a bleed into the circuit which alters the pressure difference and the density.)

Here's some of Mike's tips on removing those tubes without damage.

https://www.tapatalk.com/groups/rac...signs-and-assuming-not-t1793.html#p17512

That might be easier than drilling from the bottom unless you have a cross vise on a milling machine or drill press and can index the well accurately???

another thing that can help the situation is to open up the idle feed restriction in the secondary metering plate. the old bulletins say to open this up to .070"; that's a bunch considering it's probably .036". I would try this to help compensate for the primary side but I don't think i'd jump to .070" if I was doing the primary side mods. going to .40"-.045" would make a noticeable difference in area.

It's a pretty good size passage, I might try it sometime.

So I accessed the idle jet from the bottom of the metering block. It is indeed .022" I opened it up to .033" I've JB welded the set screws and will give it overnight to cure before it start it up again.

Thanks again guys for all the tips.

If you clicked on the first link Mattax posted there are some good pics of the baseplate.
I don’t know if all of this list number carb were the same as that one, but that carb had no actual secondary “idle” circuit.

There were only some slots/feed holes positioned well above the throttle blades....... so they contributed no additional fuel at idle....... so making the feed restrictions for that circuit bigger shouldn’t have any impact on the idle a/f ratio.

In one of the other links where another person was playing with one of these carbs, they also referred to the lack of that circuit, which is also used to keep the fuel in the secondary bowl refreshed.

don't be afraid to play with reducing the idle air bleed i.d.

I based my comments on a 1971 race bulletin carb mods. maybe the bulletin and me are off base,....lol.

I guess I would have used a fuel resistant pipe thread sealant.

.033 is a good starting point. Maybe a littlke larger than I would jchanged to in the first test but that's OK. That should give you room to drop the idle timing. Even if it means 10"Hg manifold vac, the restriction is less it may all work out.

As far as IAB and IFR. They do pair together. If you find the fueling is too rich off idle, or it needs a little trimming at idle, open the IAB up.
Don't forget you can also get some adjustment on the idle fuel ratio by changing the transfer slot exposure slightly.
So take the time to try different combos before drilling again.

I’ll just add this, as a reference on where you might need to end up with regards to ifr sizing.......

In my experience, when using cams similarly sized as what the OP is using...... if one had a normal Holley aftermarket performance carb that had the traditional 2 corner idle circuit....... like a 4777(650dp), or older model 4779(750dp, before they came with 4 corner idle), or a 3310(750vs), you would find that those carbs would have marginally acceptable idle circuit capacity(it wouldn’t be good enough to where I could leave it with the stock calibration).
And those carbs all had the fixed secondary idle discharge ports contributing to the fuel flow, in addition to having a more performance idle calibration(as opposed to the factory emissions calibration with a stock cam that provides nearly 20” of idle vacuum).

What I would do to solve the idle quality issues on those carbs in motors with big cams, where the rules didn’t prohibit it, is to install 4 corner idle....... which nearly doubles the idle fuel flow capacity.

You can’t do that for Stock....... but you could get creative with some replaceable idle feed orifices installed in the secondary side of the main body or baseplate.

While a std performance Holley carb with a normal 2 corner idle circuit would definitely be an improvement over the factory 383 carb in terms of low speed operation........ if you swapped it out for a carb with 4 corner idle you’d see how much better still it could be.

Right now, with the tiny ifr and lack of any additional idle fuel flow from the secondary side....... I’m going to say the low speed operation bar is set extremely low.

I agree on trying to come up with an idle feed for the secondaries. I don't think it could be that difficult. I can't get those taptalk pictures (keep getting 500 ERROR,....?) but I know from working with a factory avs with no secondary idle circuit that hoops have to be jumped thru to get enough fuel for even a higher vacuum stocker. I don't think a .033" idle jet by itself will cover 4 holes letting air in; especially with low vaccum, but it's a bunch better than .022". I think i'd find a standard vacuum secondary holley and study the circuit and see if it can be duplicated. bet it can.

Here ya go Lew.....

Notice the trough that allows primary idle mixture to also be discharged into the secondary side.

Secondary side has transfer slots sitting high on the baseplate.
No discharge ports below the blades.

so if no fuel goes thru the secondary slots, and I can see were there may not be much with slot not being on the suction side of the throttle blades, then what does the slot do? my thoughts were; if there's an idle bleed boss on top of the body it can be drilled, and the body had a passage down to the base plate, then why couldn't it all get connected. . tricky part will be the base plate. of course without something in hand to look at I know i'm making some assumptions. IIRC the metering plate was similar to a 6pak and I know back in the day I understood the idle feed restriction, but i'm sure I didn't understand the relationship between all the parts and passages. anyhow, it's all a thought.

I know from playing with a factory 440hp avs with no secondary idle circuit and switching to an edelbrock 1407 that does have a secondary idle circuit there's almost night and day difference in low rpm engine burn and vaccum. I never thought a lot about how dramatic the difference was until this discussion. I know from playing with 6paks the primary carb circuit is really screwed up and needs mods. none of us do the mods so we just compensate for the problem by going after the secondary idle circuit which I think makes the engine burn dirty. I know the 1407 burns a lot cleaner than the avs. circumventing ma-mopars smog crap can be a brain teaser.

First thing I’d do is get a performance calibrated 4160 carb body(like a 3310) and see exactly how the secondary idle ciduit is done on one of those, then duplicate it....... along with using a tunable secondary metering plate.

In the past, when I’ve used those with big cams, I’d just remove the plate and swap to a block...... and then add 4 corner idle.
Which is also what the guy did to the carb in the link.
However, neither of those things are legal for Stock.

i don't think it would be rocket science to duplicate the 3310 or similar design.

For sure.

The carb in the link had the secondary air bleed channel drilled all the way through to the bottom of the main body and into the baseplate where the transfer slots are.

I don’t recall the 3310’s being that way(but they might be).
That’s really the main thing I’d be looking at.

Finally got to fire it back up. Previously I left the idle at 1400. So now after warming it up, 150F, the idle is at 1100 and sounds rougher. After adjusting the throttle back to 1400, mixture screws are pretty ineffective, best setting is 1 turn, before was 1.5-2 depending on what wire I had in the bleed. I think it's now too rich, so I will open up the bleed. Any suggestions ? These are the stock bleeds, so I don't want to go too far, but I dont want to do this in 10 steps either if I can help it.

Can you stall it by closing the mixture screws?

Judging by the pics of the baseplate, the primary slots look rather long.
My guess is....... there is too much showing after you opened the blades more to change the idle speed from 1100 to 1400.

Have you qualified any of the other low speed concerns?
Still starts good?
Idles any better/worse in gear?

Also, what is the idle speed in gear, and what is the vacuum reading idling in gear?

1400rpm is too high to try and adjust the mixture screws. i'm skeptical about being too rich if the only idle feed is two .033" jets. you don't think your pushing thru the needle and seats do you? I have you measured the seat orifice to see if it's in that .075" range? you may have more than one issue going on.

Before I opened up the restriction, I could stall it no problem. Only about .03" of the slot was exposed. Now, you can;t stall it. I'm sure I now have the throttle blades opened up enough to be on transfer system. It was hard to start this last time. Before that easy to start. RPM in gear hasn't changed much. Now idle speed in gear is 1100 10.5 vac. Idle is 1400 13 vac

With this cam, not sure how low the idle can go. Before I opened the restriction, mixture screws were responsive. Remember the throttle blades drilled, so I don't have to open the throttle too far. Except for now since I opened the restriction

That’s amazingly high vacuum in gear for that combo.

My 383, with slightly more cam was about 7-8” in neutral and 4-5” in gear.

I’d probably start by just lowering the idle speed a bit and seeing how it behaved.

I'm impressed too. guess I finally got the intake sealed......

I have a choice of .069 and .072 to open the bleed from .066. going to try .069 now and see what happens

The idle quality now is much rougher. It's not going to like lowering it.

I guess the question that may not have been asked is......

If it was idling fine before, with the blades in the proper position, mixture screws in the proper range, and it was starting well, had plenty of vacuum, etc....... exactly what was the issue you were trying to cure?

Leaner idle mixtures often run “smoother” and quieter...... but the idle in gear isn’t as strong(the motor won’t stay running in gear and the engine speed just starts to fall off).

My good reworked 850DP sounds like you added 10* of camshaft duration compared to using most normal carbs(at idle and low speed part throttle)....... but it actually makes the motor idle stronger in low vacuum situations.

I would say your idle vacuum is unusually high for a typical Stocker(I have no idea why that is).

Going to a richer idle circuit is a crutch to provide adequate idle fuel when the signal(vacuum) is quite low.

13” is more in line with what I see in a typical hot street/strip car.

As I already mentioned "I've done a fair amount of working on this carb and it's functioning "OK" but could use quite a bit of fine tuning. As far as the IFR goes, the engine idles decent, but has wanted to die when put in gear. "

At .069" started it up and idle went to 1700 and sounded much better. Lowered it to 1400, screws 1.25 out. idle vac12.5 in gear at 1150 10 in. So basically idles in gear at the same rpm, but sounds good and doesn't seem like it's on the verge of dying. Might be done with this experiment.

i'm not convinced .033" IFR is too large. I didn't think you could go that big on that tube, but .033" IFR with .066" IAB isn't outrageous. I think there's something else going on. I know this isn't apples to apples but this morning I took the plugs out of my '65 coronet 440 with two edelbrock AFB's. I run four .036" idle jets plus whatever the secondaries are doing and that's a lot of idle jet area. I couldn't be happier with plug burn.

ok, I just ran some numbers. going from .022" to .033" increased the area 225%, that's a lot. so going from .066" to .069" is about 9.5%. so maybe a 9.5% correction isn't bad at the IAB. i'd still look at stuff like leaky power valve (fluttering), float level/fuel pressure vs small needle and seats. i'm done; good luck!

ok, I thought I was done. the 225% is high (I think). the .022" jet is 44% of the .033" jet, so maybe about 150% change. still a lot and further than I have gone.

Obviously iiwii....... and if it’s working good that’s really all that matters........ but it seems really odd to me that adding 003” to a .066 hole(+.0003197sq/in)in an idle air bleed would change the idle speed by 300rpm.

The rise in rpm surprised me too. Hey, I'm at a loss in explaining any of this stuff, just reporting what I'm seeing.

The .033" is really a shot in the dark. But you know once I think about it, did I just only change how much the mixture screws are screwed out ? I started at .022/.066 with screws at 2 turns out. Now at .033/.069 at 1.25 turns out ? Surely there's more to it than that, can't be that simple..........

as fuel volume increases (more jet area) then more control may be needed (mixture screws). the mixture screws are like a faucet; they control volume. you did a very noticeable volume increase.

You’re right..... it’s not that simple.

The air bleed/ifr relationship determines the A/F ratio mix of the circuit.

The mixture screws adjust the volume of that mix to the discharge ports.

No ? kinda does sound that simple to me. To change the ratio, I have to increase the quantity of fuel, which I did with the bigger jet. To compensate I ended up closing the mixture screw which reduced the fuel and air. Same amount fuel in both cases. Of course I"m generalizing here, but on a course level that what it seems to be. But you guys are the experts, I'm just trying to learn. thanks again.

If you say so.

Does it idle in gear better than before?

If so...... then it’s not really the same...... is it?

I don't know Dwayne. Idle quality is pretty subjective. But since I've been working on it, it must be better In all seriousness, I'm not sure I accomplished much in how the engine runs at idle, but I've learned a little.

The way I look at it is this......

It’s a race car. It doesn’t have to have the drivability of a Camry.
At the same time, having to do a bunch of fancy foot work with the brake and gas pedals isn’t acceptable to me either, or having it try and die after the burn out.

If it starts good, idles reasonably well in gear, doesn’t try and die after the burnout, and requires a minimal amount of two footing while driving around in the pits...... in my mind, for that application....... it’s fine.

When it was a race car with a rowdy cam, I’d never leave my car idling in gear for any length of time.
I’d click it into neutral and let it bounce happily along at 11-1200.

Only during the times when it had pretty mild cams in it did I ever leave it idling in gear at stoplights, etc.

Agreed. The car does all those things. I take that from your prospective nothing was broke, and I get that. But I like to tinker with stuff and trying different things is how I learn.

I imagine with a .022” ifr it would have been a little finickier than I would have lived with.

I would have probably tweaked it too.

Here's something out of the FSM concerning the secondary idle system

I don’t know how your particular carb is set up, but the one in the link, that i posted the pics of the baseplate of....... that carb doesn’t have the constant idle discharge ports.

The guy working on the one in the second link didn’t have pics, but commented how his carb didn’t have them either.

Also, the FSM diagram of the secondary idle circuit air bleed system doesn’t coincide with how it’s described to be routed in the first link.
Instead of being directed into the secondary metering plate, it goes straight to the bottom, into the baseplate....... and the author of the thread describes and has pics of how he re-routed that part of the circuit.

Are they all like that? Who knows.

You have two of those carbs, right?
Maybe you could see if yours is like the one in the FSM, of the one in the link.

As seen here...... no constant idle discharge port:

Here’s an old 3310 baseplate....... it has the constant idle discharge ports:

i thought it was stated that the metering block didn't have a IFR,...? the schematic shows different, but that schematic has a different metering plate than what I thought those HP383's had,....? anyhow, from what I see I think the discharge port, IFR passages can be added. no secondary idle fuel circuit sure makes'em more difficult to tune.

That’s what I was saying earlier.
If the carb being used here doesn’t have the constant idle discharge ports...... I’d be adding them, along with whatever mods to the main body were necessary to facilitate the proper function of one of the aftermarket metering plates that can utilize std jets(like a QFT 34-2).

Here's my baseplate. It looks like the idle port is fed from the primary side, I think Dwayne mentioned that. The secondary metering plate idle channel lines up the air bleed and into the baseplate as a slot above butterfly.

Maybe the diagram from the FSM for a 440. The manual says the diagrams for the 4160 for both 383 and 440 is generic. Just saw that mentioned in the manual. My bad

I have the QFT plate in it now. It's idle well matches up the hole in the body. I'm thinking the slot that is fed by it is really functioning as a transfer slot since it's covered up at idle. Not sure about that though....

Even if there was a constant idle feed port on the secondary side, below the slot(like the 3310 has)....... if the channel in the main body goes straight through from the air bleed to the transfer slot well in the base plate........how much fuel could possibly be pulled from the rear idle well with that set up?

Frankly, I don’t see how the rear idle circuit is functional at all(at idle) with it feeding only the slots, which are well above the vacuum source.

However, making that circuit functional at idle is just going to make it richer...... and from what you said previously...... that doesn’t seem to be what you’re looking for.

Adding secondary idle fuel would be used when you couldn’t get a decent idle from the primary side idle circuit, and/or you’re way out on the mixture screws and they were basically ineffective and the idle was still lean.

Since you’re only out 1-1/4 turns on the mixture screws....... it doesn’t seem like you need more idle fuel.

My guess is, the added area of having 4 discharge ports pulling on the ifr is a reason why it’s working with such a small ifr.
Similarly to how using boosters with larger feed holes(all else being equal) will be richer than boosters with smaller feed holes...... when using the same jet size.

whether you chose to complete a secondary idle circuit or not is your choice but I did do some more thinking. the quick fuel plate you have does have an idle jet, IIRC .036"; or at least the ones I have do. I don't like those plates because they wouldn't let the float in my 6pak end carbs work freely. I know you have side pivot floats so that may not be an issue. if you look at the fuel passages from the jets to the booster discharge tubes on the QF plates they are of small volume, like 600 or 750 holleys. the instructions I had said to install the plates directly to the bowl gasket/carb body; not using the spacer plate and gasket that holley uses. this allows the bowl gasket to squish inside those runners consuming more runner volume. so, the secondary system is much larger, throttle bore/venturi, with more air flow but doesn't have the fuel passage volume of the primary. so what was gained? if it were me i'd rather have something like a factory 6pak plate which has much larger runner volume, using the factory spacer plate and gasket which also has a .036" idle jet and some are .093" which I think is about all you need. this would be similar to factory stock. to my knowledge all the big vacuum carbs, holley 3bbl/6paks, came with the larger runner volume plates.

If you buy the QFT plate kit for the side hung bowls, it comes with a clearanced float.

And I agree with the gasket getting squished into the channels could be an issue if higher fuel flow is req’d, and that using the steel plate with the thin gasket is preferred.

I’d probably shorten the Jets a little if it would give me enough to add that steel plate & gasket back on the carb.

Although, I’m pretty sure that if you buy a new generic 4160 carb(3310/1850, etc), the steel plate and thin gasket are no longer installed in those carbs.

My original plan was to use the QFT plate and make it easy to change the main jets. Then when I have the jet size figured out, I could modify the stock plate and put it back in. The rule book says you can modify the fuel and air passages. So I don't know if it's a big stretch or not, but it would make things much more servicable if I can leave the QFT plate in there and also use replaceable air bleeds.

The plate did come with a modified float. I don't like it as I'm not confident of what the float level is. It's a different design and I don't think the factory dimension applies. This added to the fact the bowel has no sight plugs or externally adjustable floats makes hard to know where the level really. In the FSM they show a cool site glass that use one of the bowl screw holes as a source.

I like the idea of the 6 pack plate.

I'm still trying to understand just how the secondary idle air bleed, idle restriction and slot are supposed to work. Is it really a secondary transfer system ?

look into the 6pak plate and the option of using short drilled 6-32 brass set screws for removable jets; available on amazon. I don't think that would be difficult and the "jet" entry point would be lower in the fuel bowl than the QF plate which would be a plus on the secondary side. the only real plus I see with the QF plate is jet extensions if needed.

Thanks. do you know the holley part number ?

the plates I have have a 34r-6153-b number. they also have a 35 stamped on them that used to indicate orifice size but it seems holley may have gotten cheap on the re-pops and one size fits all. anyhow, that's no big deal. the largest orifice is .093", which I think may be ideal, but if it isn't those orifices can be opened up. the 6-32 set screw thing gives you options. one option is drilling and tapping the power valve channel restrictions for the 6-32 like the race carbs. doing this will allow you to do the power enrichment from the power valve, which is it's job, and not rely on the main jets for power enrichment which is not their main job. think of the carb as having and idle circuit, cruise circuit (jets), and power circuit (power valve channel restrictions). I think using the main jets as the sole source of enrichment just muddies everything up. looking the 1971 race bulletin it shows using #69 main jets on the primary side. that's pretty large for the size of those venturi and throttle bores. bet they weren't looking at playing with the power valve channel restrictions.

I looked at some plates I have. The one with the largest main well and jet is stamped 45. The well measures .115 x .160 and the jet is .097. The main well in the QFT is smaller, .115 x .122 I would really like to use the 45 plate for multiple reasons.

The power valve is plugged. Seems easier to tune for WOT without it.

Does your race bulletins list any staggered jetting for use with the stock cast iron manifold ? I've heard that staggered jetting in necessary, but I don't see how I could figure that out with just a WB. Maybe one day I can put it on a dyno with headers that have EGT sensors.

taking the power valve out is like giving the carb a lobodomy. whoever the dumbass is that told you to do that quit talking to him!!!!! that puts the carb in the power circut full time. don't do that on the primary side UNLESS the engine won't make enough vacuum to use a power valve; your engine makes enough vacuum. this could very well be part of your problem; maybe most of it. there is a proper way to remove the power valve and i'll bet it's not done correctly. tune power thru the power valve channel restrictions not the jets.

the service bulletin i have doesn't give any staggered jetting. it does give some crummy advice for tuning the accelerator pump system. those iron intakes don't flow much air and i do think they have distribution issues. the only correct way to tune for this is EGT at each exhaust port or knowing how to read the plugs after a run. i think you have other issues to deal with first.

Yes that's all the secondary slots do on most carbs.
The metering plate (yours has a metering platte?) has an IFR and may be placed to give a little extra shot of fuel mix from the well as the secondaries open.

With photos of the main body faces and the metering block and plates it would make it easier for us. Use some air or carb cleaner to figure out connections that are not clear.

It is interesting they did not include a weep hole on the secondary side. if nothing else it helps insure fuel is replaced in the carb even when driving around town,

I agree with Lew. Work on fuel distribution later - using the spark plugs and mph results at the track.
The carb already has fuel distribution modifications in it that go with that intake. That's what the notches and tabs on the boosters are for.
If the intake is modified, then the boosters may need some changes again. That's often what you see in the DC /MP bulletins.
Some of those are here: http://www.moparts.org/Tech/Archive/fuel.html

As far as using the PV or not, if everything is idle to WOT it could be OK. I know some guys do that. But if there are times that during staging or burnouts not at max load wot, then maybe not so good. Shouldn't be effecting the idle either way, however sometimes it does.


As far as the idle mix screws, IFR and IAB goes, these are not linear relationships.
IFR controls all the liquid fuel going from main well to idle tube in your case. The IFR is always submerged so changes in restriction should d owhat you'ld expect.
Then the IAB (assuming just one) bleeds a little air into the fuel (when the manifold is at lower pressure.) As long air mixes in as tiny bubbles it moves the fuel along faster and reduces the density.
Some of this fuel, in fact a fairly good portion of the stream is goes to the transfer slot where more air is being bled in from the top of the slot.
The rest goes to the idle port and can be trimmed with the idle mix screws. In this carb's case, special idle mix screws.

That advice came straight from AED. I spoke with the head tech guy. His advice on a drag only car, if foot-braking use a PV, leaving on a 2-step as I do, remove the power valve. As I have mentioned, this carb has no big problems. There are 3 areas where I want to improve.

First improve the idle quality and reduce the tendency to die when placed in gear. Still in the middle of this. I

After launching, there is what I will call a flat spot. Not a bog. You can see it on an rpm graph. It's not significant, but it's there. I've tried pretty much all the different vac pod springs.

Fine tune the A/F at wot. It started very lean, now it averages 13.0 so I'm getting close. The left and right are always different, that's why I've mentioned staggered jetting.

Just thinking out loud here, but I wonder if increasing the contribution of the secondary transfer slot will help in launching the car, keeping in mind I leave off a 2-step....

It does have a weep hole, its just fed from the primary idle circuit. If we're talking about the same thing.

Game plan for now is put removable air bleeds in the main body. I have another metering block to use that uses screw in IFR, and I will use the oem metering plate I found with the larger main well passages, this will allow me to go back to the oem float. I'll post pics when test this out and then take it back apart.

I appreciate the feedback

No its not the same at all.
Its fed from the same set of circuits as the primary. It doesn't matter there are two exit ports in the secondary. The pressure difference on the restrictions and bleeds is the same.
The only advantage is distribution of fuel is possibly better.

A secondary side weep hole adds fuel from a different circuit. A full secondary system would double the fuel flow at idle (if it was identical to the primary side).
Generally secondary weeps serve to keep fresh fuel in the bowl because most people didn't actually open the secondaries often in everyday driving. A little richer at idle also was generally not a problem until reducing CO and HC out the exhaust became a priority.

Tune to performance. The WBO2 is just a reference. If its steady through the top gear on the track, then changing jets for best et and mph. MPH is more consistant indicator of top end power.
The worst cylinder will be the limiting cylinder. Best way to figure out what's going on inside is to look at the spark plugs.

How would you add weep holes to the secondary ? Here's pics of my baseplate, both sides

Same as shown on that 3310 a few posts back.
It's just a tiny weep under the t-slot.
Might have to extend the well. Can't see down in the photo.
You could try it, and if it doesn't work out, pack it with lead.

Sounds like a good idea. I'll do that. Waiting on a new metering block.

So I was looking forward to putting the carb back together with the new metering block. Not happening this week, the padded mailer showed up with the box that the metering block was supposed to be in. Box was empty, a separate package with new metering screws was in there. The mailer had been opened. Pretty annoying. Kind of strange it was just the block missing. Supposedly another one from holley is on the way. Never had that happen before. Also had a fraudulent charge on my visa a couple of weeks ago. Sign of the times ??

Question while I wait for a new metering block. Should I make a hole in the gasket for this idle air bleed hole ? Picture shows a hole in the center body that connects wiith the idle air bleed, but the "standard" gasket has that passage to the metering block blocked off.

This is why I didn't want to give any specific advice.
Show us the top, the metering block both sides.
if you have the throttle plate off show us the bottom of the boosters as well.

Spray some carb cleaner through that hole and tell us where it comes out.

One we know that, we can have some confidence about what connects to what and make some judgment calls.

It is connected to the idle air bleed and lines up as shown in the picture. I'll post pics of the new metering block whenever I get it along with lots of other pics.

New metering block, baseplate and body. Waiting on some 6-32 set screws so I can finish IFR. I'm good with dialing in the idle. Any suggestions in general or improvements as respect to launching on a 2 step, please chime in. Cheers.