383 Built with a "Lumpy" cam - Running too Rich - Will Change of Metering Rod Springs Help?

[Sport Fury 67]

Has anyone had any experience in changing the step up springs for the metering rods in a Edlebrock 1406 carb, in order to lean it out, so the engine does not run so rich.

Right now, my plugs are as black as a coal mine and the mileage is hovering around 8 mpg. The engine originally was configured as a 383 - 2 barrel in a 1969 T&C wagon, that was re-built with a "lumpy" cam. The carb was upgraded to a four barrel Edlebrock 1406, with a HIREV 7500 HiPo electronic ignition.

I have see articles and videos where people have changed out the set up springs for the metering rods, to a lower tension spring, based on the manifold vacuum at idle, to lean out the carb.

Some other comments state the rods and jets in the 1406 are designed for these carbs to run "rich" out of the box.

Other comments also stated you should also adjusting the timing in combination of the above.

Before I start changing several parameters, I would like to inquire if anyone has made similar adjustments on a 383- 1406 combo. The goal is to up the mileage and eliminate the damp black carbon exhaust spray on start up.

Any comments would be appreciated.

 

[CBODY67]

What are the cam specs? What idle rpm? Is the carb new or has it been rebuilt? Where is the base timing and what is the total timing at 4000rpm? What intake manifold? Does the motor oil smell of hydocarbons?

It sounds like the richness is across the board, but is it really just at idle? What jets are in the carb now? Most of the comments I've seen in here is that the 1406s might be more toward the lean side of things.

The mpg you quote certainly is low, but in what vehicle and what rear axle ratio? Is that mpg on the highway or in the city?

Just curious,
CBODY67

 

[Cartel]

THERE IS A "thumb" on the carb linkage that press's the secondaries closed. some times it needs to be tweaked so that the "finger" on the primary forces that thumb up and holds the secondary closed tight.
you may have to hold the carb wide open (engine off) and bend that thumb so the finger press's it and seals the secondaries when you let go. back the idle screw off so that it gets done without hanging up on it then set it later and recheck that the thumb is held tight and butterflies are closed

 

[CBODY67]

Is there not a spring wound around the secondary throttle shaft to keep the secondaries closed? Usually is on Carters and similar, from what I've seen. Might be out of sight, but it's there.

IF the secondaries are cracked open more than a certain amount (as the Holley 4bbls are, as they have an idle system on the normal 4160s, to keep fuel in the secondary float bowl fresher, if the secondaries never open), the hot base idle speed will be affected by that minute bit of opening.

Just some thoughts,
CBODY67

 

[Cartel]

there is but I have been here before. just a suggestion.
you can also look down the carb when its idling and look if any drips are coming out the secondary venturi's
you can also grab that thumb at idle and try to twist it closed youself and see if you hear a change in idle.
sometimes the spring doesnt cut it.
I guess I'm thinking lumpy idle and not the other functions that would make it rich going down the road.

also black smoke at start up I found is it boils the gas out and into the engine after you shut it off or too much fuel pressure

 

[CBODY67]

As you mentioned "fuel pressure", what kind of fuel pump and at what fuel pressure when running?

CBODY67

 

[MONC440]

Until the OP provides more info I will reserve my comments because there are many variables involved in tuning carter/edelbrock carbs. I have set them up many times for single and twin carbs. The hardest one was setting two up for use on a tunnel ram with a big cam that had extremely low manifold vacuum.

To answer one of your questions, yes set your timing first. Also report back what your manifold vacuum pressure is at idle. If you have low manifold vacuum and tight springs on the rods the rods will be open all the time, or open way to soon and you will run very rich.

 

[Toolmanmike]

Here's a good video for basic set up and calibration. He has many videos on the Edelbrock carbs. This one is probably the first step.

 

[57fury440]

Edelbrock 1406 carbs are set up to be on the lean side. All the advice above is good. That carb should work really nice on a 383. Are you running dual exhaust? Do you have the specs on the cam as that would tell us how mild or aggressive it is.