Pig rich mixture at idle 2 x 4 Gen 2 hemi

[Beekeeper]

I’ve been working on this hemi build trying to lean out the rich idle mixture and getting
nowhere with it. 496 stroke Hemi 11.5 to 1
compression with stage V custom heads the cam is a bullet roller [email protected] .638 lift
110 separation. Two 650 AVS2 carbs will be ran 1 to1 on the linkage and want use a factory PCV.

Here’s where i’ve been on it. Plugs are AR53
gapped at .032 running factory prestolite dual point distributor Initial timing at 18 degrees it idles at 1000 rpm and won’t idle any lower it just dies.
Has 10” of vacuum and is pretty steady the fuel mixture screws have little if any control
of idle speed. I have changed the main jets and rods twice to try to lower the amount of fuel but this has had no effect on the
mixture.
I pulled the carbs to check the idle transfer slot exposure and looked like too much. So I
Back the curb idle screws out and set them 1 turn in after contact but it will not run there.

In my research on these carbs it looks as the only way to adjust the idle mixture is with the mixture screws. It seems as the main jets regulate off idle and cruise and secondary jets wide open throttle.
I know the idle circuit get fuel from the main jet but it acts as if changing them doesn’t effect the issues I’m having with rich idle.

Want to try the NGK5ES plug but was hoping to get this rich thing corrected first. I’m getting fuel in the oil and it doesn’t take very long so i’ve changed oil twice now and around 1 hour run time for both combined.


So i’m here for Help and any ideas on tuning
these carbs. This is my first ever dual 4 barrel set up.

 

[moparedtn]

I wouldn't think you'd want to idle the thing on two carbs (factory didn't, right?), but what do I know?

Engine is probably bad. I'll be happy to come by and relieve you of it if you need me to.

 

[Beekeeper]

I wouldn't think you'd want to idle the thing on two carbs (factory didn't, right?), but what do I know?

Engine is probably bad. I'll be happy to come by and relieve you of it if you need me to.

 

[Beekeeper]

My understanding is the stage v intake will not work with progressive carb set up. In looking at the intake it would lean out the front 4 cylinders.

 

[pnora]

What is your fuel pressure?

 

[Beekeeper]

What is your fuel pressure?

5.5-6 psi

 

[khryslerkid]

I have changed the main jets and rods twice to try to lower the amount of fuel but this has had no effect on the
mixture.

Have you experimented with the metering rod springs?

 

[RemCharger]

Maybe needle+seats are leaking? Or floats too high?

 

[Beekeeper]

Have you experimented with the metering rod springs?

Yes sir I have opened the covers for the rods/piston and watched them they are down and not dancing up and down. Even went as far as removing the springs completely so the rods were down for sure.

 

[khryslerkid]

Yes sir I have opened the covers for the rods/piston and watched them they are down and not dancing up and down. Even went as far as removing the springs completely so the rods were down for sure.

Float level?

 

[Beekeeper]

Maybe needle+seats are leaking? Or floats too high?

I have checked the floats 3 times on both carbs the first time they were off a little but they are spot on. With the top inverted needle valves closed I can’t blow air past them with my mouth. These are brand new carbs i know they can still have issues but they are new.

 

[moparedtn]

It would be cool to have some O2 sensing going on here...

 

[khryslerkid]

I have checked the floats 3 times on both carbs the first time they were off a little but they are spot on. With the top inverted needle valves closed I can’t blow air past them with my mouth. These are brand new carbs i know they can still have issues but they are new.

If my 2x4 was a little closer to your build I could probably help. You're dealing with a lot more compression and cam. Less vacuum also.

@dvw set me straight on what I was dealing with when I was tuning mine. He'll more than likely help with yours.

 

[Dragon Slayer]

The engine idles on the idle circuit, which has nothing to do with main jets, or rods and springs. The primary venturis have idle jets which is a tube in the primary well off bottom of venturi. You also have the idle air bleeds in the venturi body. The design is to have an over rich mixture at the idle screw ports and in the transfer slot. That way the idle screws can control the amount of fuel mixing with inlet air pass the slightly open blades. If you close off those screws and you still have an idle mixture available it has to be from an exposed transfer slot because of blade opening, or a leaking fuel into the venturi. Fuel level too high in bowl, some other issue.
You probably should have one carb blades closed, mixture screws fully in and run on just the rear carb and see if you can dial the mixture in right. Once you can, then you can turn off the rear carb and dial in the front. If you can't dial them in and the motor running rich you have to have a fuel leak somewhere, I would think.

 

[khryslerkid]

The engine idles on the idle circuit, which has nothing to do with main jets, or rods and springs. The primary venturis have idle jets which is a tube in the primary well off bottom of venturi. You also have the idle air bleeds in the venturi body. The design is to have an over rich mixture at the idle screw ports and in the transfer slot. That way the idle screws can control the amount of fuel mixing with inlet air pass the slightly open blades. If you close off those screws and you still have an idle mixture available it has to be from an exposed transfer slot because of blade opening, or a leaking fuel into the venturi. Fuel level too high in bowl, some other issue.
You probably should have one carb blades closed, mixture screws fully in and run on just the rear carb and see if you can dial the mixture in right. Once you can, then you can turn off the rear carb and dial in the front. If you can't dial them in and the motor running rich you have to have a fuel leak somewhere, I would think.

Wouldn't you be starving four cylinders and creating a super lean condition in those cylinders by closing off one carb?

I first tried a progressive linkage on my 2x4 and had a lean condition on the front four cylinders that was way too hot. That was with a working carb.

 

[moparedtn]

Looking at pics here, it appears that particular intake is open plenum from front to back, yes?
If so, then the front cylinders most certainly are getting at least some percentage of their charge from the rear
carb and vice-versa, whether at idle or not.
If that's the case, this is going to be one heck of a balancing act...

 

[Beekeeper]

It would be cool to have some O2 sensing going on here...

I do have O2 sensors on both banks and they read like it’s running lean but my nose says otherwise and the fuel is getting in the oil and the plugs are black.

 

[AR67GTX]

You must have a big cam. With the exposed transfer slot and no control over the secondary blades like a Holley, you could drill small holes in the primary blades to let more air pass while closing the primary blades down and gaining idle mixture control. Start small, no more than 1/8” to start and increase in small increments until the blades close down the transfer slot sufficiently. But some will consider that a drastic move. I would explore Dragon Slayers recommendations before drilling holes.

 

[Beekeeper]

Looking at pics here, it appears that particular intake is open plenum from front to back, yes?
If so, then the front cylinders most certainly are getting at least some percentage of their charge from the rear
carb and vice-versa, whether at idle or not.
If that's the case, this is going to be one heck of a balancing act...

Ed,
The plenum in this intake is not open front to back there’s is a small opening up high to equalize pressure but fuel isn’t gonna make it through it very easily.

 

[Beekeeper]

The engine idles on the idle circuit, which has nothing to do with main jets, or rods and springs. The primary venturis have idle jets which is a tube in the primary well off bottom of venturi. You also have the idle air bleeds in the venturi body. The design is to have an over rich mixture at the idle screw ports and in the transfer slot. That way the idle screws can control the amount of fuel mixing with inlet air pass the slightly open blades. If you close off those screws and you still have an idle mixture available it has to be from an exposed transfer slot because of blade opening, or a leaking fuel into the venturi. Fuel level too high in bowl, some other issue.
You probably should have one carb blades closed, mixture screws fully in and run on just the rear carb and see if you can dial the mixture in right. Once you can, then you can turn off the rear carb and dial in the front. If you can't dial them in and the motor running rich you have to have a fuel leak somewhere, I would think.

Dragon,
Here’s a diagram I been looking at on the idle circuit.