71 Challenger, 2.76's, 27" tires.

Stock 5.9L Magnum with RPM airgap. Idles at 20"Hg, Timing is 16° - 35° by 2800, Vac advance is in use

Carb: Slayer 600 VS

PV - 8.5 (was 6.5, too much throttle required for enrichment)
PVCR - .041 from .052 (was dropping from 14:1 to 11:1 at open, now drops to 12.2)
Mains - 70 (was 68)
Secondaries - 71 (was 74)
IFR - .028 from .031 (was only 1/4 turn open on idle screws, now 1 1/4)
Spring - Brown (second stiffest), was yellow
Bleeds - should be OK, AFR does not drop or climb through the RPM band during light accel.


-Idles at 12.5:1 at 650 RPM
-Moderate Tip-in still has a hesitation with the pink and orange cams, even though accel pump squirt is instant.
-Off idle through 2800 rpm stays between 14:1 and 15:1 as long as acceleration is light, staying above about 10"Hg.
-Cruise is 80mph at 2800 rpm, 18"Hg. running about 14.5:1. Smooth and happy.
-Moderate acceleration (~5"Hg.) causes a nasty, sustained bog above about 2000. AFR reads 12:1 and runs TERRIBLE unless I go WOT. It will sustain this bog as long as I hold about 5"Hg, which is easy considering it can barely accelerate since it is running so bad. If I go WOT, it clears up in about a second and pulls very nicely to 5000 and maintains about 12.5:1. The secondary spring is brown, the second stiffest, and it made almost no difference over the soft yellow. I haven't tried the black one yet.

The mid-range bog is about to drive me to EFI. I can't leave a stoplight at anything other than Grandpa or Punk Kid, and it lean pops no matter what at tip-in. Passing a slower driver results in a sustained bog/backfire unless I go WOT to get out of it.

Ideas?

Sounds like typical secondary bog, but I'm almost topped on the springs. I have LOTS of vacuum, but vac secondaries are tied to velocity thought the carb barrels causing vacuum under the venturis, not manifold vacuum.

Get a real/better carb from someone who knows how to tune em and you will forget about EFI...........

I have a set of SV1 carbs that give me a problem when slowly tipping the throttle open.From Idle to WOT it's good.I spoke with the designer of the carbs and got some great tuning advise.
In your case you need someone like THUMPER to get your carb happy so you van be happy and keep your hair!

What is a "Slayer"? Edit, never mind, I looked it up as that is a new one on me. I would be calling Holley Tech first, sounds like a defective carb, has it always done this?

Dom,

Do you have an engine mild enough to test/tune my carb on? I can meet you any afternoon for a hand-off. I've got co-workers who live in Victorville that could deliver or at least get it close. I'm just west of you in Quartz hill and work at Plant 42. I may even throw in a Holley Ultra HP 950 that needs to be tuned for a 625HP Chevy 427 to be a driver, not a drag racer...

RE: Holley tech... No help. I wrote a 2 paragraph explanation of the issues and all changes, and happend to ask what size the factory IFR size was. I got no actual tuning help, but they did, however, provide me a cool list of all the factory parts and sizes.


SL-600-VS
MAIN BODY PRIMARY SECONDARY
PUMP NOZZLE 0.031 N/A
BOOSTERS 45312-1 45312-1
B-PIN SIZE 140 140
HIGH SP AIR 0.031 0.031
IDLE AIR 0.073 0.033
INTER AIR
SLOT RES
600 main body
METERING BLOCK hr block/cast plate
MAIN JET 68 74
POWER VALVE 6.5
PV REST. 0.052
EMUSION .028/.028/.028
KILL BLEED 0.028
IDLE FEED RES 0.031 0.042
CROSS CHAN. .144
FLOAT BOWL

NEEDLE/SEAT 100 100
FLOAT TYPE BRASS QFT NOTCH
THROTTLE BODY
1 9/16
ACC. PUMP 30cc
CAM PINK
Throttle Shaft round slabbed

1-1/2 turns out on mixture screws

It sounds like to me that you need to lean down the primary side power valve restriction channel by around 1/5 of the current diameter down to .030 or so
That should lean out the AFR at 5.0 vacumn at part throttle cruise enough to make it not bog on the transition on both the primary and power valve circuits IMO You know your motor likes 12.5 or leaner at part throttle cruise, correct
Doesn't AFB Plant 42 have new exotic testing equipment?

What if you had a leak, between the main body and the baseplate.

(right about now is when somebody says it never happens)


A stock engine really shouldn't need to idle at 12.5:1. I understand if the mixture screws were enriched in as a test for driveability effects.

Cab, if this was a jet, we'd be in business...

What do you mean by "at 5.0 part throttle cruise"

I'm already down to a .041 62% of the original .052 PVCR area. Do you mean more? 2/3 of my .041 is a .033.

I edited my post to make it a little clearer, hopefully
Some motor like rich AFR and some don't, most of mine like lean AFR

maybe it's a fuel pressure issue. I've seen borderline high pressures overcome the floats ability to control flow. this is very noticeable at WOT.

In my original post I mention that everything except idle is 14 - 15:1 until the secondaries or P.V. come into play. Even 85 - 90 mph is sitting right on 14 - 14.5 turning about 2800 - 2900 and pulling 18 in.hg.. Secondaries opening/open and or accelerating enough to get below the 8.5" PV point is 12's.

I'm not inclined to think so. I rn a Holley red all the way back at the tank. The bog is perfectly repeatable. A fuel pressure issue with an electric pump would not be, and would tend to be worse at lower speeds with less fuel being used or air moving. I can transition in and out of the bad spot at will.

Shoot for 12.5 or leaner AFR on the transition on the part throttle driving Test, test and tests some more until you love it
How many people in Quartz Hill now? How about Pear blossom ?

I'll throw in my .02 and that's twice what my advice is worth.

In my entire life, I've NEVER seen an application where a vacuum secondary carb is called for. I know some carb Giants and gurus like David Vizard leg hump those carbs to death, but I've used enough of them in real life to know its a [censored] to make the secondary side happy. In fact, I've been on the dyno several times with decent street/strip stuff that at 7000 didn't pull the secondaries all the way open. Just worthless. A double pumper is more tuneable than a VS will ever be. The fallacy that you can run a bigger VS carb is complete horse crap. 99% of the time, you operate on the primary side, so how did the VS help?

That said, you have to work with what you have, or buy a better carb.

I'd start over and unhook the O2 sensor. Then I'd tune the big out of it and make it run. Then put the O2 back on and tune from there.

I'm going to say that the best money you'll ever spend (unless you enjoy working on stuff just to say you did it) will be spent send the carb to someone like Thumprdart or Mark Whitener and let them help you. It will be cheaper and quicker in the long run.

FWIW, I trust my ability to read a plug long before I trust any sensor. But I'm very comfortable reading plug. I'd make it run first and then tune it. The O2 isn't perfect, and can screw you.

For all the screaming and whining I hear about no two flow benches or dynos read the same, why would anyone think that every O2 sensor reads the same? Is it leak free? Is it mounted the same? Who knows?

Make it run and then tune it. And where it runs the best is the numbers you use for your O2 sensor. Timing lights read differently. And whatever you do, don't flow Holley jets. You'll see what production tolerances look like.

Don't get caught up in sensor numbers until the car performs.

One last quick thought...did you every verify cruise manifold vacuum? You may still be bringing in the PV circuit too late. I'm betting you cruise at 18 inches, maybe a bit more. That's a huge drop from 18 to 8.5 and that delay means you have to cover that hole with accelerator fuel or fuel from somewhere.

Here's my original request to Holley for some info...


Your Question Was:
Slayer 600: Excessively rich idle and WOT

Idle mix screws only 3/8 turn out, but still 12:1 idle A/F, cant get it to target 13.5. Engine runs excessively rich cruising anywhere below 2300 RPM, but then leans out nicely to 14:1 at 2500, then falls below 11:1 any time the secondaries are open. I have already backed the secondaries down to #71''s. Main jets were fattened to 70 to get the 14:1 before secondaries open. Previously was 15:1 or higher with 68''s. I need to restrict down the idle system.

I know I can increase the idle air bleed size to get the mix screws back in range, but I would like to know the factory idle feed restrictor size to test reducing it as well. PV has been checked and is not blown.

Thank you,

Dan


Holley's response:
ifr .031



WOW. Thanks Holley.



Yes, cruise vacuum is high teens at just about any speed. Verified 18 at 2800 rpm steady state doing 80 on level ground. I dropped the PV opening for a few reasons. Whether they are correct or not remains to be seen.

1) The engine is not high power, meaning even small accelerations require a fair bit of throttle, dropping the vacuum significantly and hitting the PV unnecessarily.
2) The PV was dumping in so much fuel is would go from 15:1 to 11:1 with the factory .052 PVCR's. That doesn't work AT ALL with mild acceleration.
3) The secondary bog seemed to be from opening too soon, so as I delayed the secondary opening to a higher load/throttle position, I moved the PV opening with it.

I'm with Zippy here, double check for vacuum leaks. I had a vac secondary carb that i had to throw a really odd tune at because it had a leak at the body/baseplate. worst tendency was a lean backfire or lean stumble, i jetted that thing up like 6 steps before i realized the vacuum leak..and it was actually driving good at that point.

now on the truck, I have a QFT HR650 (mech sec) on a basically stock 318, it's been quite nice on my truck. cruise rpm is around 2800, idle vacuum is about 18.5"
only thing with the carb is I only have the idle mix screws about 1/2 turn out, that was after dropping the IFR to .028 (oddly the ifr change didn't really change where the motor liked the idle mix screws). the .028 was just a touch lean but I left it for a long time.

Recently the truck started running a little bad, especially when cold, lean stumble and then it got to where it didn't want to drive smooth at partial thorttle opening.
I drilled the .028 IFR to .0292 and it helped a bit. Then I got to thinking, let me go and tighten up the manifold bolts and the carb bolts. BAM, the thing is a freaking pleasure to drive again, even when the motor is still cold now...

I've always run 9.5 power valves in that motor...

Are you SURE that the bog is due to the secondaries opening? Is it possible that the issue is with the primaries? Have you tried unhooking the secondaries? Have you tried locking the secondaries to open manually with the primaries?

I suggest all this to try and have some impact on the bog, for better or worse. And to verify that you are blaming the right culprit. Once you can impact the bog with a specific action, you know what area to concentrate on.

The idle would seem to be an easy fix with a smaller IFR. And the cruise is usually acceptable around 14 and you know what to do to dial it on in since it responds well to your changes.

A quick and easy way to test an engine's response to a smaller IFR is to insert a strand of wire stripped from a piece of 16 or 18 guage wire. I usually use one piece 2 or 3 inches long to go from one IFR to the other. It's easier to handle and can't get lost inside the carb.

Try as small a strand as you can find because it doesn't take much on the IFRs to make a big difference. Even .008 or .010 will probably be too much, but it will verify that you are doing the right thing.

The wires can be used in most any bleed or orifice to experiment. Right now, finding what impacts your bog directly is job one.

Don't need a "mild" motor to test on and most 4150's just get modded, assembled and shipped unless they're a BLP with a dual pattern base plate. Hit me up and I will set ya up and give you enuff BLP jets and bleeds to keep ya busy..... 760-900-3895.....