6 Barrel outboard idle question

[mbtownsend]

I've read all the different 6 pack tuning articles and it sure seems straight forward enough but I'm getting an odd result when I'm setting up my idle. I just had the 3 carbs rebuilt by a holly guy in town that other mopar 6 pack guys recommended. I set the outboard idle mixture screws at 1/2 turn out. Car fires up fine. I have an AFR hooked up and the car idles pretty lean (16.0). I back the main Idle Mix screws out a little at a time all the way to 2 1/4 turns and I'm still at 14.5 to 15.0 and the car does not idle well that lean. I have a promax set up and take outboard carb idle screws out to 1 full turn and the AFR goes to 17?

By opening the idle screws on the outboards I should be getting richer not leaner? Any thoughts?

 

[68 HEMI GTS]

When you open the screws you enrich the idle. Your A/F reading sounds skewed. Go back to a 1/4 turn out. Set them by covering the IAB method. The A/F meter is a tool not gospel. Set them where it idles good and ignore the meter readings at idle. If it idles good you’re close. My meter doesn’t always give proper A/F at idle. There’s several factors that can play into it including the camshaft. The outboards are a trim control and don’t require a whole bunch.

 

[mbtownsend]

Thank You. Appreciate the input. I'll try it right now.

 

[vance.dykes]

use a vacuum gage it will tell you how the engine is running the highest reading is what you are looking for when fine tuning a carb. make sure your base timing is set first then tune the carbs. use carb cleaner small spray at base for vacuum leaks. or the hoes's hooked up are not cracked. is the oil fresh an a f r can be off if there is gas in the oil.

 

[yella71]

Are the floats set right? start at the beginning and adjust from there.

 

[mbtownsend]

I set them back to 1/4 turn. Adjusted main carb with vacuum gauge and it ran best at 2.25 turns out. still a rough idle at stop signs. Car shakes a bit. I may turn the outboards out another 1/8 turn and see if the main idle screws come in a bit.

 

[mbtownsend]

I checked floats first thing. I tried the IAB method on the outboards and got zero change either way on either carb. I also tried the IAB at 1/2 turn out and got zero change so I'm wondering what's up with that?

 

[RJRENTON]

Are the floats set right? start at the beginning and adjust from there.

I agree with the premise in that fuel level effects overall fuel delivery from idle thru w.o.t. If the fuel level is low the overall mixture will be lean. Another thing to check: is the end carb linkage correct allowing additional air flow, causing a lean condition. Is it possible that the rebuilder increased the size of the idle air bleed orfices of the end carbs? Or decreased the size of the idle feed restrictions in the metering plates of the end carbs or changed the metering plates? Did the rebuilder increase the size of the holes in the butterfly valve discs in an effort to allow for better off idle transition in the center carb? These possibilities are in addition to those suggestions by others. Its highly unlikely that there is significant throttle shaft leakage but that is always a possibility. Air/fuel ratio is nice to know but it is not absolute....its just a tool. Some people prefer setting mixture by vacuum readings, I perfer the RPM method, others like A/F ratio.
BOB RENTON

 

[68 HEMI GTS]

I set them back to 1/4 turn. Adjusted main carb with vacuum gauge and it ran best at 2.25 turns out. still a rough idle at stop signs. Car shakes a bit. I may turn the outboards out another 1/8 turn and see if the main idle screws come in a bit.

yep, very small moves now on the outboards. Sounds like the IFR might be too small on the center carb. Is it the original metering block? Also what’s the base timing and engine set combo/cam?

 

[mbtownsend]

Stock cam. Superbird. Initial timing is 10 and 34 all in at 2200.
Promax Metering block. They set it up for my location so unsure what IFR they used. Main jet is 64 center and 84 outboards per their recommendation.

 

[mbtownsend]

Stock cam. Superbird. Initial timing is 10 and 34 all in at 2200.
Promax Metering block. They set it up for my location so unsure what IFR they used. Main jet is 64 center and 84 outboards per their recommendation.

Scratch that. Just rechecked timing and it said 20 initial and all in at 41. Better back that off to 35.