Technical Edelbrock 1406 only idles on primary circuit... Questions? Ideas?

Hey all,

Firstly, I hope Im posting this in the right spot - Ive come to my wits end and after lurking I've decided to post.

Im doing a 1947 International Pickup build, initially the plan was to keep it original, but the motor was just too pooched. So instead I dropped in a Kijiji find 350, and have been cobbling together parts to get this thing running.

Well she runs.... sort of. I cannot for the life of me seem to get it away from idling on the primary circuit through the transfer slots? (hoping my terminology is right here). I've read a number of tech articles that state you shouldn't have more than a square of those visible with the throttle closed. If I back the idle off, no matter what I do with the mixture screws it bogs out and dies. Almost like its not getting enough air. Its chugging through gas - something to the rate of 300ml per 10 minutes of run time. Its visibly rich, with all spark plugs sooty, and the fumes stinging my eyes.

I can get it to idle no problem with the mixtures screws fully turned in, at about 800 RPM. If I dial back the idle screw, and let out the mixture screw, it wont idle. Conversely, if I play with the mixture screws at 800 rpm it prefers them almost all the way in, maybe 1/4 turn out. Vacuum seems to be ok. In order to get it to idle, I've blocked everything off - not using power brakes so plug in the rear. PVC either plugged or routed into valve cover (breather on opposite side) but it doesn't seem to make a difference. Passenger side port plugged, drivers with my vacuum gauge on it. At 800~ it pulls about 15 inches, and runs smooth but rich. The timing it pretty tough to read, as its hidden down there, but I believe I'm at about 10-15 degrees of advance (distributor advance not hooked up). Adjustment here doesn't seem to do a whole lot, as I attempted to give it more advance with the idle turned out, but the mark was way over. Compression is a wildcard - my chinese compression tester showed 85-97 PSI across the board, which seems wayy too low. However, it seems responsive when running. Battery was low when cranking, other plugs still in, and throttle closed. So id imagine its higher, but still close.

Im hoping someone here has an idea - I've heard stuff like advance timing more, or drill holes in the butterfly to let more air in. I've got two of these carbs, and tried with both, both have been cleaned and put back together. Im wondering at that point if I should just be ok with the butterfly exposing the transfer slot and run it with the mixture screws all the way in??

 

Check fuel pressure.

 

Like saltflats says, check fuel pressure, and also check to make sure that the needle's are staying down in the jet while at idle and not bouncing. It wouldn't hurt to check the float level and drop too. Are the jets and needle's stock or have they been changed, or what is the set-up you're running now?

 

NO!!!!!!.........don't do that and don't go drilling holes in the butterflys!! NO...NO...NO!
First......check for a vacuum leak around the base of the carb.
Get it running some how,,,,and spray carb cleaner around just the base of the carb where it bolts to the intake. IF it speeds up OR dies replace the carb gasket.
AFTER that check (If no change) remove the top of the Edelbrock "carefully...don't lose the little cotter pin and notice which hole the accelerator pump is in... Is the bowls full of fuel? Is there crap in the bowls? Remove the air mixture screws (NOTICE how many turns they are from closed/seated)
Squirt some carb cleaner in the holes and see if you can blow out any debris. Re-install the screws and GENTLY seat them. Then screw them back out 2 1/2 turns. Put top back on and check to be sure the metering rods are not bent .
IF it still don't run right try advancing the timing (turn the distrib) a few degrees.
Once its is running....turn the distrib some more and see if it gets better and engine revs up!
Check back and let us know!
6sally6

 

Had a Edelbrock that wouldnt idle. Turned out it was the accelerator pump. They have a plastic stem that hooks to the linkage,and when they get old they take a curve which must cock the inside seal screwing things up. Start it,and push the stem straight with your finger,and see if it suddenly idles correctly.

 

Needles are down, fuel pressure is good. Tried it with a gravity feel bottle as to no overpressure - no change. Remove and cleaned mixture screws. Still no change.
Will try with spray tomorrow and the accel pump suggestion.

Rods and jets are the factory ones - at least I believe so.

After tuning properly, when you flip over how much of the transfer slot should be visible?

thanks all

 

This is a carb that came on an engine but was missing some linkage, thing looked new other than the linkage. I took the top off (removing the metering rods and springs first) gave it a once over, all parts were stock and accounted for, floats set right, I replaced the missing linkage and stored it on the shelf.
A friend stopped by wanting to borrow a carb because his was pouring fuel out, I let him have this one, he said it ran perfect without touching it and he used it all season before returning it. Here's how the slot looks.

 

Is this carb new or at least rebuilt? Verified clean?

 

You didn't mention what intake manifold you are using.
Most of the time you need an adapter plate when using the edelbrock carb.
Even when using an edelbrock intake.

 

^^^^Edelbrock manifold, 1406 carb, EDELBROCK gasket! ^^^^

 

I've run into this several times with Edelbrock carbs. I'm surprised that no one has mentioned what E10-E15 fuel does to the low-speed idle circuit on these carbs...so much so that the fuel mixture screws will eventually do nothing. Time for a rebuild/cleaning or a new replacement.

To avoid and fix this, a buddy turned me on to Star-tron...a fuel additive for 2 stroke engines. 2 tanks full will usually clean up most of the problem, but you should see improvement on the first 1/2 tank with the additive.

 

I was getting there. But OP never came back.

Most of them I have opened up lately have been full of "gel"

 

Hey all!

Thanks for the responses - I’ve been tinkering.

I have been flipping between 2 x 1406. One was on a running 350 Sbc. And the other was rebuild by me. I was a Qjet guy in the past, so not overly terrible at rebuilding carbs.

Metering rods checked and work on both. Running a standard 80’s Sbc manifold with everything plugged. Using the correct 4 hole edelbrock spacer to adapt it. All gaskets are new and good. Have also replaced plugs and plug wires, rotor and cap look good. I am wondering if its a camshaft issue, as I have no idea what the previous owner put in it and could see the front cover has been replaced recently, as the rear frost plug had been into at some point...

Sprayed around the base of the carb with cleaner today, and base of manifold. No detectable leaks.

After playing around a bit I pulled the PCV hose. When I did that it was audibly sucking air in and the idle sorted right out. I was able to back off the idle speed on the side (to a position where the transfer slots were closed, or nearly closed) and finally the mixture screws were responsive to the point that I could tune the car and achieve 14” of vacuum.

Of course the problem is, it’s pulling all its air off the pcv valve hose (bad) and fuel from the idle circuit (good). If I plug the pcv back in, the only was to get it to idle is to crank in the idle screw so that it’s running off the primary circuit again. PCV seems to jiggle audibly, which I believe means its OK.

Not really sure where to go from here… but I will say it was extremely nice to be able to have that vehicle at idle for an extended period of time and not have my eyes burning! So I guess that’s progress.

 

Do you see fuel dripping from the boosters at idle with the PCV disconnected?

 

take the idle adjuster screws out and blow with compressed air.I just went through this carb cleaner would not do it but air did. Runs great now.

 

Did not check for fuel drip from the boosters at idle….

I have however removed the mixture screws and sprayed multiple times.

 

How many turns out are your mixture screws from gently seated closed?

What is your observed ignition timing at idle?

What is your desired idle speed?

 

With the pcv hose off, and the transfer slots closed 1.75 turns out. Approx 7-800rmp. Base timing is 10 degrees. Vacuum around 14-16”

with the PCV on and idle screw where it should be, unable to obtain idle for longer than 30 seconds. Vacuum at approx 8”

with the pcv on, idling off of primary circuit, best idle is with the mixture screw fully close, 10 degrees and 14-16”. Approx 7-800 rpm.

 

Did you pull the top and check the float levels?

 

Turn your screws out to 2-3/4" turns.

 

These are not fuel control screws. They are air and fuel control screws.

Too far out and too far in are both bad.

Since it idles better with more air coming in, you are either restricting the idle air too much, or you have fuel dumping in. That requires a float level check.

An Edelbrock carburetor is like a bathtub. The can only really spill over the top. If your float level is too high, it will end up in the engine.

 

That is excess fuel delivery.

There are only a few ways to get that at idle with an Edelbrock:

Fuel pump pressure overcoming needles, pushing them off of the seats, over filling the bowls, and dumping over into the barrels. Edelbrock carburetors can have no more than 5.5psi.

-or-

Float levels outright set wrong.

I find them wrong all of the time:



7/16" clearance, using a drill bit of that size as a go/no-go gauge. As measured in the center of the long side of the float.

That should equate to 15/16" to 1" drop.

 

I’ll recheck the floats. Did them this way the first time. I still feel like it’s a “not enough air” condition. Does the idle circuit draw air in from anywhere else besides through the main butterflys?

 

That is not where it draws air from.



Find where it says "air bleed", and "low speed passage".

 

Shown here:

 

Make sure and double check your fuel pressure reading, it needs to be 5 - 5.5, nothing more or it reaks havoc.

 

I suspect this isn’t the first time gimpyshotrods has come through! Thankyou sir.

Was able to get it tuned up today, removed the top, took special care and attention to the passages he mentioned. Used a piece of welding wire to really get in there.

Also, after looking at his picture with the float set with a 7/16 bit under it, I tried it that way. I had previously set the new floats to 7/16 at the leading edge using the little paper sqaure. Leading edge is now quite a lot lower, but the drill bit contacts 1/2 thru.

Thankyou for everyone who helped me out…. Was getting ready to pull my hair out. And goes to show that you can do something right a ton of times, but do it wrong once and you’ll be chasing your tail!

 

Every once-and-a-while I get one right!

 

I use 1oz of Star-tron with every fill up which is usually 12 gallons in a 17 gallon tank. I’m not sure if it has helped but in 8 years with 1953 WCFB’s it sure hasn’t hurt because they run perfect.

 

Late to this thread; but glad you got it. I went through a carb that was abandoned by PO because it was "junk". Float level and float drop were both way off. Blew carb cleaner through air bleeds, and the removed mixture screws. Re-assembled with original parts and gaskets and it ran fine.