Random low idle issue 1406 edlebrock carb

[Javin]

Hi I have an 1982 gmc 3/4 4spd 350 today it started up fine ran good just as I was pulling into work it started to idle at 450isb where it usually idles around 750. I looked at everything visible no signs of anything obvious. It’s got a 1406 edlebrock carb, it’s about a year and half old never liked it from the start really. So I took the truck out again seemed like it idled fine again but shortly it just drops off and it smells really rich. Anything off idle runs good. Could there be an issue with the carb itself? Ive done a lot of maintance things on it Over the past year ie, plugs wires distributor air cleaner fuel filter, adjustable fuel regulator so nothing is really old as far as maintance things goes. Any help would be greatly appreciated

 

[yevgenievich]

It might be loading up due to either needle/seat leaking overflowing the fuel bowl or excessive fuel pressure

 

[Javin]

It’s interesting I was taking to a guy at work about it with much more carb experience than me, he noticed my clear fuel filter only had a bit of gas in it even when running it’s only half full he figured it should be completely full? He said it maybe the floats restricting the amount of fuel coming in or low fuel pressure, my regulator is set to 5.5psi I’ve never changed the fuel pump as well. How would I check it loading up? Also I covered the carb by my hand best I could and it didn’t die which leads me to think it’s running lean

 

[crazy4offroad]

Change your filter out for a Wix paper element fuel filter if you're using one of those nifty glass/screen cleanable filters. They let a lot of garbage past and these carbs are notorious for the idle circuit getting clogged. And when it clogs it acts exactly as you're describing.

Fortunately it's an easy thing to check/fix. Run your idle air screws in, counting the turns, then once you know how many turns out they're set to, unscrew them all the way out. Apply air pressure to the ports where the screws go, regulated to 20 psi. A few blasts should do it. Run the screws all the way back in, then back them out the number of turns they need to be set at. Be sure to change the fuel filter first or you'll just be doing this again. Although don't be surprised if you do have to do it again, there are screens under the 2 needle and seat assemblies that may be holding garbage that may work its way through.

If it doesn't fix it, it may very well be the float height/drop, which isn't hard to set either. There's 3 rods with little clips on them, you have to take them off and take the rods loose (choke, accelerator pump and secondaries). Then take the 8 top screws out and remove the carb top. Have a 7/16" drill bit handy and a tape measure. Flip the top upside down and measure float height with the drill bit. Between the end of the float and the gasket the drill bit should just slide under. If it don't, bend the attachment bar between the hinge and the float to set it. I use needlenose pliers for that. Next, flip the top right side up and measure float drop with a tape measure. You should have 15/16 to 1" drop from the gasket to the end of the float. You adjust drop with the little angled stop tab at the back of the float hinge.

When you put the top back on, you may need to take a torx head driver and loosen the 2 screws that hold down the cover over the metering rod assemblies. Just loosen them a little and the cover will rotate out of the way letting the plungers and metering rods pop up. Once the top is down all the way the plungers will push down easily.

 

[Javin]

Thank u very much for all the info I’ll defiantely be doing this in the next or so, would it be possible to use one of the air in a can to clean them out? Also just to be clear you can keep the carb on the truck while cleaning out the idle circuit? I set the floats about a year ago the same time I updated a few things that would make it my 4x4 friendly but I haven’t had it apart since might be an idea to check floats as well? Also the filter I have is not cleanable but is a clear plastic filter with that paper filter inside do you think this is alright? I replaced it about 2 months ago

 

[crazy4offroad]

That filter should be alright if it looks like it doesn't have a bunch of junk in it. If in doubt though look for the Wix brand filter, that's what was recommended to me when mine was having trouble. And yes you can do all this with the carb on the truck. I tried canned air once and didn't have luck, an air compressor would be better. Volume vs pressure I think.

 

[yevgenievich]

The smell of fuel made me think too much fuel, but could be otherwise as well. Usually when carb loads up with too much fuel and idle speed starts dropping there will be black smoke out of the exhaust. Not enough fuel just as described above

 

[Javin]

So I just tried blowing out the idle screws and it didn’t seem to do anything I tried adjusting the idle screws had it running good then took it for a drive as soon as I go off the throttle it’s back to idling crappy... I don’t have time to check the floats today but I guess that’s my next step

 

[Javin]

Yeah I think it’s not enough fuel as well.. anything off idle and it runs great so you figure the floats might be off eh, what cause them to go out of alignment?

 

[Javin]

So just to update I daily drive my truck halfway thru the day she’s running good, I’m guessing something dislogged in the carb idle circuit??

 

[bucket]

Might have been old/dirty fuel. Like Curt said, Eddy carbs are very sensitive to fuel quality.

I had a similar issue once and I learned my lesson from it. From now on when I pump gas out of a vehicle I'm pulling apart, those gas cans are only used to fill the lawn tractor.

 

[Javin]

Hmm good to know Im still going to run some carb cleaner thru it and monitor it the next couple days I’ll keep an update on how it’s running

 

[crazy4offroad]

If your truck has the old rubber fuel lines you may want to change them out for urethane or some other material that isn't affected by ethanol in modern gas. When I first started noticing problems I took a long pick and cleaned a ton of debris out of the fuel passage in the carb where the fuel line connects. Ethanol breaks down rubber, and the passage had at least a tablespoon full of these tiny black specks of decomposing rubber. Since I cleaned it out and changed the lines I've had no more trouble, even with the truck sitting over the winter.

And yes, it is entirely possible the idle circuit, or even the needle-and-seat cleared the debris on its own. Hopefully it didn't make its way into one of the venturi passages or some other hard-to-clean section of the carb.

Another good telltale way to see if the idle air circuit is plugged, remove your air cleaner and while it's running, look at the primary squirters. If they have fuel trickling or spitting out of them kind of sporadically then more than likely the idle air circuit is plugged. The engine vacuum draws fuel through the idle circuit towards the bottom of the carb, and when that system is plugged the vacuum starts pulling fuel from the primary squirters, making the mixture too rich and the idle out of whack and too low.

 

[Javin]

Yeah it does have the old fuel lines might be an idea to switch them up eh, I did look into the carb while it’s running and there wasn’t fuel coming from the primary squirters but I still figure something was plugged up... I kind of want to still pull the top off the carb see how the bowls look inside as well as the float levels

 

[crazy4offroad]

Usually the fuel lines will start to feel weak and soggy, the opposite of dried out old vacuum lines. If you have a long skinny flathead screw driver you can take the fuel line loose from the carb, run it back in the passage and spin it a few times and pull it out. If it's getting a lot of that disintegrated rubber, it will be built up on the end of the screw driver.