Pig rich mixture at idle 2 x 4 Gen 2 hemi

[Beekeeper]

 

[RemCharger]

Looks good if you've got gaskets and the pipes are tight.
You could pull the plugs and tighten the gaps to 25-28.
Also, dual point... I haven't worked much with those, but they have to be set just right I believe..

 

[RemCharger]

Pipes sure look clean

 

[Beekeeper]

Pipes sure look clean

Good eye but that’s before I fired it up with the O2 sensor and pipes.

 

[Beekeeper]

You are running a cold plug and they can foul easy on a hemi probably even more so with a Stage V manifold and all that idle fuel and points. Granted you have high compression, but you might want to try a hotter plug as you sort this out.

Hotter than a NGK 5?

 

[moparedtn]

Pardon my ignorance here, but would a 19.5:1 A/F be excessively lean?
Seems like I recall a better target being around 14:1 at idle and maybe 13:1 at full pull?

 

[dvw]

There is no way the O2 readings are anywhere close to accurate with pipes that short. Never had trouble with two Eddys idling with stock air bleeds, even with a [email protected]" cam. If the blades are open to far to maintain idle speed. A; initial timing is to low. B; converter is to tight. C; vacuum leak. You can drill the throttle plates to increase airflow with the blades closed down to maintain the correct transition slot gap. But I've never had to do it with a pair of Eddys.you can always solder the holes shut if you want to go back. 3 cars all running 600 or 750 Eddys. All drive and idle fine. Smallest cam is a [email protected]".
Doug

 

[RJRENTON]

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.

IMO....contrary to popular opinion, idle and off idle fuel transition circuits ARE NOT CONTROLLED BY THE PRIMARY JETS OR PRIMARY METERING RODS, THE STEP UP PISTONS AND SPRINGS. On origional Carter and aftermarket Edelbrock/Weber remakes, ALL idle and off idle fuel is controlled by the primary booster venturii assemblies via internal non adjustable metering orifices. These internal orifices CAN BE enlarged but reducing the sizes is almost impossible.
Do the carbs you are using have an adjustable main air bleed or a throttle stop screw on the linkage side. If, the idle mixture is too rich and the mixture screws have little affect, auxiliary air bleed holes may have to be drilled into the primary throttle plates opposite the idle transition slots in the primary bores. Is your setup opersting like the origional HEMI setup? The front half of the rear carb is the primary carb and the front half of the front carb is not used to control the idle, but has a stop screw on the primary throttle plates set to a dimension. 90% of the idle adjustments are done on the rear carb. But if your setup uses both front and rear carbs in unison, then both carbs require simultaneous adjustments to balance air and fuel flow for equal division of function. Just my opinion of course.
BOB RENTON

 

[Beekeeper]

Doug,
Are your 3 cars dual 4 barrel setups? Only reason I ask is Khryslerkid mentioned you helped him with his setup. Thanks for replying here for (A) does 18 degrees initial sound low? (B) no converter it’s on the run stand (C) It”s possible it could have a vacuum leak does it seems that the vacuum gauge would not be steady if it did? I’m pretty much a newbie when it comes to a hemi and also to dual 4 barrel setups.

 

[Beekeeper]

Bob,
The carbs are 1905/1906 edelbrock 650 AVS2 carbs. I’m not a carb expert by any stretch but I do understand how the idle circuit works in these carbs. If I have to drill the primary throttle plates I will but only as a last resort. I think my biggest issue is I can’t get this beast to run without opening up the primary throttle plates so much that it’s exposing too much of the transfer slot. Now why that is I’ve yet to determine. I will be running g it some more this evening and trying a few things mentioned in the thread I’m hoping you guys can help me get it sorted out. And to answer about the setup no not like the original hemi setup these are 1 to 1 on a stage 5 single plane intake.

 

[dvw]

Doug,
Are your 3 cars dual 4 barrel setups? Only reason I ask is Khryslerkid mentioned you helped him with his setup. Thanks for replying here for (A) does 18 degrees initial sound low? (B) no converter it’s on the run stand (C) It”s possible it could have a vacuum leak does it seems that the vacuum gauge would not be steady if it did? I’m pretty much a newbie when it comes to a hemi and also to dual 4 barrel setups.

Yes all 3 are dual 4 barrel. But they are also AFB not AVS. My bet is the idle feed restriction and air bleed sizing is similar. Where are the idle mixture screws set? If the throttle plates are open excessively it need more air at idle. You could try wedging something in the secondary throttle plate stops to hold them open a touch to raise the idle speed.. Then see if the mixture screws function with the front plates nearly closed. If that works make it permanent or drill the plates 3/16".
Doug

 

[pnora]

I suspect a massive vacuum leak.

 

[RJRENTON]

Yes all 3 are dual 4 barrel. But they are also AFB not AVS. My bet is the idle feed restriction and air bleed sizing is similar. Where are the idle mixture screws set? If the throttle plates are open excessively it need more air at idle. You could try wedging something in the secondary throttle plate stops to hold them open a touch to raise the idle speed.. Then see if the mixture screws function with the front plates nearly closed. If that works make it permanent or drill the plates 3/16".
Doug

I concur that there are differences between the AFB vs AVS designs. To my knowledge, I'm not aware of any secondary throttle stop screws on either existing designs, but do the current Edelbrock AVS designs offer throttle stop screws like the vacuum operated Holley carbs have? I don't think so. To "temporarily" hold open (any amount) the secondary throttle plates would be very difficult to accomplish with any degree of consistency and repeatability.
What was unclear to me was: did the OP have the PCV system connected and functional to either or both carbs? As the PCV system is a significant air bleed, IF, say, only one of the two carb's PCV system was functional, would the second carb's UNCONNECTED PCV system be providing the rich idle fuel mixture, to the point of being unable to lean out the overall idle mixture. It would be interesting to know just how rich is "pig rich" actually is in terms of the idle A/F ratio.....fouled spark plugs or just exhaust "smell" or ??.
Blocking open the secondary throttle plates a slight amount, may be the first step, but which carb? Front carb or rear carb or both? If that helps to reduce the overall rich mixture, then ideally, if one could determine the overall area increase by holding open the secondary throttle plates of both carbs, then the actual size of the of the holes to drilled in PRIMARY throttle plates of BOTH carbs could be accurately determined in terms of AREA. Total area required divided by four (4) to determine the drill size used to use. By drilling the holes in the primary throttle plates of BOTH carbs would tend allow for a more balanced air flow thru both carbs. Just my opinion of course.....
BOB RENTON

 

[Beekeeper]

Bob,
I did have the PCV connected to the rear carb. The reason I called it Pig rich is because It’s smells rich not lean and all the plugs are black and fuel is going into the crankcase and needless to say but consuming a lot of fuel. I originally fired the engine up the first time without
the PCV connected still the same mixture though I have a carb sync and did sync the carbs.
With the comments and suggestions here I think I need to look at the ignition spark and the plug heat range and timing. The dual point distributor was rebuilt and recurved and setup on a Sun distributor machine by our very own Halifaxhops (Ray). I think having to open the primary throttle plates to get it to run is what I need to determine. I truly thank and respect everyone’s help and suggestions with my engine.

 

[dvw]

If the transfer ports are uncovered to far it'll be rich. There shouldn't be more than 1 -1/2 turn of throttle plate screw to obtain idle speed. I'd use feeler gauges on the rear blade stops. Do it on both carbs. I've used the new AVS in single carb applications. One did require holes in the primary blades. The other did not. More than a few guys running them in N/SS with fairly large roller cams. When used in pairs the amount of idle air us doubled which normally allows for good idle. I know my racecar (2 750 Eddys) with a [email protected]" cam would idle at 800 rpm in gear if I wanted to turn it down that low.
Doug

 

[Fran Blacker]

Like dvw's idea on opening secondaries. I'd use a length of wire to hold secondary throttle plates open. Start small to see how it works. Wrap the wire around a screw so it doesn't go in engine, duh. If you end up drilling throttle plates I'd start at 1/16" or 3/32" holes in primaries because you have 4 of them, me I'm cautious about going big on first try.

 

[Beekeeper]

Thanks Doug I will use feeler gauges between the secondary throttle stop on both carbs to see if I can close the primaries up some.
Thanks

 

[Beekeeper]

Thanks Fran,
I’m trying to be sure that drilling is a last resort mod I have no problems doing it just want to be sure that indeed they are gonna require it. I’m really starting to wonder since Doug has them running well without the need to drill. Great idea on the wire to hold the secondaries open.

 

[RJRENTON]

Bob,
I did have the PCV connected to the rear carb. The reason I called it Pig rich is because It’s smells rich not lean and all the plugs are black and fuel is going into the crankcase and needless to say but consuming a lot of fuel. I originally fired the engine up the first time without
the PCV connected still the same mixture though I have a carb sync and did sync the carbs.
With the comments and suggestions here I think I need to look at the ignition spark and the plug heat range and timing. The dual point distributor was rebuilt and recurved and setup on a Sun distributor machine by our very own Halifaxhops (Ray). I think having to open the primary throttle plates to get it to run is what I need to determine. I truly thank and respect everyone’s help and suggestions with my engine.

Just an additional thought....using a carb synchronizing device is a great idea. But, you indicated that you did not have the PCV system innitially but now its connected to the rear carb. What about the front carbs PCV connection....is it plugged or capped off? Because the carbs are basically dedigned for a stand alone installation, connecting them in tandem, operating in unison unless the rich idle fuel mixture from the plugged PCV of the front carb, is accounted for, the resultant overall rich mixture you are experiencing, will be the result, IMO.
I'm a big fan of the Prestolite dual point distributor....which is what is in my GTX. Mine is recurved to yield ~ 36° total all in at 2400 RPM with 15° initial NO vacuum advance. Yes...initial advance will definitely effect low RPM and idle stability. But, I believe your issues are carb related as previously discussed. I'm definitely interested in how you resolve the problem. Please keep us posted.....
BOB RENTON

 

[AR67GTX]

I’m with Fran on initial hole size if you drill. With 4 of them, start small and increase as needed.