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I've got a fun one for you carb guys

67Charger

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Location
Erda, UT
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 12.4:1. 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.
 
I'd put the IFR back to stock to richen the transition circuit.
Also, clean all circuits and air bleeds. I have found debris in the main jet well on a new Holley carb before.
 
Is this to address the lean tip in?

With the IFR stock I could not get the idle screws to respond. 1/4 turn out was max before idling poorly and it forced me to adjust the carb blades outside of the ideal "visible square" transition slot with poor results. Right now I have a square, good vacuum, and and about 1.25 turns out with adjustability to either side. Not saying you are wrong, but that's where I started. All circuits bleeds have been blown out repeatedly. I did so every time I made a tuning change.

I can return the IFR's to stock to see how they work with all the subsequent changes...
 
Basically, I drive the car to work, have all day to think about this at work, and make my changes when I get home. I'll try these tonight, one at a time.
 
Out of curiosity what are the air bleed sizes? You also have the idle kind of fat for a stock motor. Squirter size? How much emulsion does it have? Are the IFR’s high or low?
 
Primary/Seacondary
HS: .035/.031 (was .031/.031)
LS: .078/.033 (was .073/.033)

I can't seem to get it to lean out any more at idle, but as soon as it tips in it leans to 14+.
 
I have a Holley Ultra HP 950 and a HP1000 that I am about to throw on there just to try. It may be terrible, but it might still be better than this annoyance. I could probably just disconnect the secondaries and have a kick-*** 2 barrel 475 or 500. Yes, I know it is a bad idea with poor low rpm signal, but what would it hurt?
 
If you think it is a secondary issue disable them and see what happens? You can wire the vacuum can arm down so it cant pull open, easy to do.

Have you tried going back to the 6.5 PV? An 8.5 PV is dumping fuel before you need it.
 
That I can do on the way home. I'll grab a few zip-ties and keep it shut to see how it behaves as a 300 2BBL without the secondaries "crashing" the party. Should just be a little short on the top end I would imagine.
 
Is this to address the lean tip in?

With the IFR stock I could not get the idle screws to respond. 1/4 turn out was max before idling poorly and it forced me to adjust the carb blades outside of the ideal "visible square" transition slot with poor results. Right now I have a square, good vacuum, and and about 1.25 turns out with adjustability to either side. Not saying you are wrong, but that's where I started. All circuits bleeds have been blown out repeatedly. I did so every time I made a tuning change.

I can return the IFR's to stock to see how they work with all the subsequent changes...

Yes, that should help with lean tip in. If the throttle was too far open at idle and into the transition, you might need to slightly open the secondary blades to let more air in so you can get the primary throttle blades out of the transition slot. If that does not work, maybe drill hole in the throttle blades. I usually only have to do that with big cam engines with low vacuum?
 
[going from memory from a year ago]
I had the opposite problem. The slots were almost covered. while trying to get the idle rpm to come down. I had to open them a little and dial the fuel back to almost closed on the idle screws. I dropped the IFR's to get some range back on the screws. Secondaries are totally closed. My super high idle vacuum seems to be pulling hard on the fuel slot. Like I said, I'm willing to try about anything, since I track my changes I can always return. I also hadn't done anything without research, reason, and testing for improvement. I just may not have been right.
 
Your whole tune is a bit off. Your idle settings affect your cruise. That thing should idle 13.5-14.5 or even leaner no problem. If it doesn’t, something is wrong. Then you’ll need to fatten the cruise back up because it’ll be even leaner. Tune for WOT last. Otherwise you’re just chasing your ***. I think your going the wrong way on the air bleeds. Also the position of the idle screws doesn’t bother me as long as they control to the desired A/F ratio.
 
Drop the IFR lower than a .025?

I'm hearing a LOT of people say lean it out. The current setting was established by setting the timing, then setting the idle mix and throttle screws for max vacuum, then reset timing, then reset mix and throttle screws, "wash, rise, repeat" to max vacuum. Lean it out anyway?
 
Your whole tune is a bit off. Your idle settings affect your cruise. That thing should idle 13.5-14.5 or even leaner no problem. If it doesn’t, something is wrong. Then you’ll need to fatten the cruise back up because it’ll be even leaner. Tune for WOT last. Otherwise you’re just chasing your ***. I think your going the wrong way on the air bleeds. Also the position of the idle screws doesn’t bother me as long as they control to the desired A/F ratio.
The carb sellers say they like the idle air screws 1.5 to 1.75 turns out.You don'y think that matters?? I am about to go with a larger IAB to get them out further then the less then 1 turn they are now.....
 
...right. I have a larger IAB to get the screws out, and the smaller IFR since the IABs alone weren't doing enough. I understand thet the IAB's fine tune the idle AFR and the IFR's are just bigger steps. I was at 3/8 turn out, now 1.25. I can dial them in a bit to lean out idle some more.
 
The idea is having a good balance. And in reality on the OP’s motor is should be super easy to tune. Sometimes it just depends on what the combo wants. Long as they have control in the desired AF range is what really matters. Just remember the idle screws work as a team with the transfer slots and the IFR and the IAB.

In other words don’t get hung up on say if they’re only 1 turn out if your meeting all your desired A/F settings.
 
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Fun curve ball. It runs WAY better when its warm (75° out or more) than when it is cold, (30° in the mornings). Both cases with the motor fully warmed up.
 
Drop the IFR lower than a .025?

I'm hearing a LOT of people say lean it out. The current setting was established by setting the timing, then setting the idle mix and throttle screws for max vacuum, then reset timing, then reset mix and throttle screws, "wash, rise, repeat" to max vacuum. Lean it out anyway?

Yes, why do you want the motor to idle fat? It’s hard on the engine, kills the plugs, sucks gas, etc. I wouldn’t decrease the IFR any more. Just go 1/8 turn in on your screws and see where that puts you. Go a bit more if needed. One change at a time then drive. Your cruise will also be leaner, you may need to start adjusting for more fuel at the transfer slots. Probably smaller MAB also. Bring the mains in quicker.
 
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