Edelbrock air-fuel adjustment

Chuck71RS

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Lifetime Gold Member
Nov 24, 2012
1,826
Houston, Texas
Have an Edelbrock 1406, w electric choke

Engine has been firing right off but wanted to adjust the a-f mixture using a vacuum gauge. At idle the engine was running kinda rough but this is not a recent change. Idle rpm is about 800.

Drove the car till full warmed up. With the engine running, the RH screw was fully seated but no change in engine running. Then the LH screw was fully seated and engine rpm increased and ran smoothly.

Removed the needles and sprayed carb cleaner into the openings. The LH had a whistling sound but not the RH. On the needle tapered end, I felt some roughness with more on the LH needle. Inserted needles fully then backout 1 1/2 turns and started the engine. Fully seated the RH then LH needle with the same results.

Sprayed carb cleaner around the cab-intake gasket with not rpm change

Circuit blockage? More carb spray? Compressed air? Watched a YT video about Edlebrock a-f adjustment having no affect due to the transfer slot being exposed due idle and fast idle adjustment settings?

Bad needles? Do the rough spots mean the surrounding carb surface is damaged?
 

Twisted_Metal

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Feb 26, 2004
31,226
Bloomington, MN
Have you looked at the transfer slot?

The exposed slot should be “square”.

If the exposed slot is longer than its width, it is (basically) bypassing the idle circuit… Which makes the idle adjustment screws ineffective.
 

jeff swisher

Veteran Member
Apr 26, 2018
1,957
Yukon Oklahoma
If it was mine I would set timing to be 18"-24" at idle.
Then see what the RPM is.

Make sure the secondary side is closing all the way on that carb.
I have seen bent linkage arm hold the rear open a bit
I would then set the carb idle speed.
And then adjust mixture screws.
I usually end up at 2 turns out or more.
More things.
Make sure the boosters are not dribbling fuel at idle.
Loosen the cover screws for the metering rods turn the covers sideways and remove the piston and rods.
Not bent?
Reinstall them.
Slide cover over the pistons but not all the way and snug the screw a bit.
You should see the piston because the cover is not on all the way.

Fire it up.
That piston should suck down and stay down at idle.
Blip the throttle and the piston should jump up.
That last has nothing to do with your idle but more about performance.
Run the heaviest spring that will allow the piston to be down at idle in gear.

If none of the above works you may have debris clogging the idle/emulsion tubes.
You will need to pull the top off and pull the boosters and check and clean.
 

1980RS

Veteran Member
Jun 17, 2006
6,253
MN
Change your 1406 to 1405 jetting specs, you will like it much better. The 1405 has a fatter fuel curve for most engines.
 

Chuck71RS

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Nov 24, 2012
1,826
Houston, Texas
The carb situation I am dealing with presently is a-f mixing. RH has no affect when turned from 1 1/2 turns out to seated and LH raising rom 150 or so when turned from 1 1/2 turns out to full seated. With both needles fully seated the engine fires right off and idles fine.

Removed the mixing screws, filled with carb cleaner, blew compressed air in, saw a fine mist come out of the carb surface but same mixing needle condition

Vacuum leak? Float adjustment?
No vacuum leaks. Capped all four vacuum fittings, and vacuum reading same as before (15). Sprayed carb cleaner on the gasket edge with no rpm change. Gauge on ported registered 0 as it should

Have you looked at the transfer slot?
Have to remove the carb to see the transfer slot

And then adjust mixture screws.
The RH screw has no affect when 1 1/2 turns out or fully seated. LH raises RPM 150 or so and engine runs smoother

1406 to 1405 jetting specs,
Maybe something to try later but first I need the carb basics to work
 

1980RS

Veteran Member
Jun 17, 2006
6,253
MN
The carb situation I am dealing with presently is a-f mixing. RH has no affect when turned from 1 1/2 turns out to seated and LH raising rom 150 or so when turned from 1 1/2 turns out to full seated. With both needles fully seated the engine fires right off and idles fine.

Removed the mixing screws, filled with carb cleaner, blew compressed air in, saw a fine mist come out of the carb surface but same mixing needle condition
Then that circuit is plugged with crap. You may need a wire to go in there and clean it out. I got some nice jet cleaning tools when I bought a Snow blower carb last year off of Amazon, came with the little carb for $15. So far I have used it on a few Holley's cleaning debris out of small plugged holes already.
 

Chuck71RS

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Lifetime Gold Member
Nov 24, 2012
1,826
Houston, Texas
It is possible that the needle has broken at the tip, even a minor scuff will change things
Both tips looked uniform and could not feel unevenness. Moving a fingernail on the tapered surface, I felt a few rough spots on both. Swapped each to the opposite side 1 1/2 turns out. This morning, drove to warm engine then full seated RH then LH. Same as before
Then that circuit is plugged with crap
Will get a fine wire and try cleaning out the circuit. I am using a Fram G-3 fuel filter. Fram tech said the filter is 90% for 20 microns
 

Chuck71RS

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Lifetime Gold Member
Nov 24, 2012
1,826
Houston, Texas
Does the circuit the a-f screws seat in also connect to the transfer slot?
I think I have reached the point where I need to remove the carb to visually check the slots.
 




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