Edelbrock 1406 failed emissions

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rich weyand

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Ever since finishing the EDDY 1406 re-build, I noticed I had an off idle hesitation. So I started experimenting with the accelerator pump, tried all three settings, and it still had the hesitation. Then I experimented with different step up springs for the last week or so. My hesitation went away after I put in the 8hg springs, and the accelerator pump at its highest setting. Its running extremely well. I'm loving the gas mileage increase with the new jets. I drove to Phoenix and back to Tucson on a little over half a tank of fuel, the last time I did that before the tuning, I went through both tanks.

Yeah, that's what I'm running -- the 8" springs and the accel pump on the highest setting (i.e. richest setting, the hole closest to the pivot).

What are you getting for mileage now?
 

VAL

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Yeah, that's what I'm running -- the 8" springs and the accel pump on the highest setting (i.e. richest setting, the hole closest to the pivot).

What are you getting for mileage now?

With the 700r4, 3.73 gearing, and 35" tires, I calculated 16-18 on the freeway, averaging 70mph. Before the carb tune, it was right around 7-10 mpg. I haven't been doing much in town driving, but my guess is, it will improve dramatically also. I'm baffled by the difference in the MPGs and performance that I have now.
 

rich weyand

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So 3.73:1 with 35" tires is equivalent to 3.09:1 with stock 29" tires, plus a 700R4 with overdrive? Yeah, that's about the mileage you should be getting.

You're baffled because of a fundamental misunderstanding. Horsepower is not a function of how much gas you burn, but how much air you move through the engine. For a given amount of air, the maximum horsepower is at the correct mixture of gas. ADD GAS above the correct mixture and the horsepower and the mileage BOTH go DOWN, for two reasons. One is that the extra gas is not being burned, it's just wasted, killing your gas mileage. Two is that the additional gas displaces air that you could be moving through the engine, so the horsepower goes down as well.

This is why turbocharging and supercharging and nitrous add so much horsepower. Turbocharging and supercharging blow more air through the engine. Nitrous has more Oxygen atoms per molecule than air, so it is as if there were more air going through the engine. People don't blow GAS through the engine, they blow AIR through the engine. You need enough gas flow to keep up with the air at the proper ratio, but more gas alone makes things worse, not better.

Just some dumb numbers. Let's say you are moving fifteen parts of air per second and one of gas per second. That's about the right mixture. So you will get the horsepower associated with fifteen parts of air. Add gas, so you are running too rich, so that now you have two parts of gas per second. Well, the second part of gas won't burn, not enough air, so it's just wasted. But it's worse than that, because now you only have fourteen parts of air. The other part of air you could be moving is the wasted gas. So the horsepower goes down to what you would get with fourteen parts of air, not fifteen. So you are using more gas, and horsepower went down.

You were running way rich, because Edelbrocks are set up for a wide range of different engines, and our truck engines are a poor match to their factory jetting. (Which is also the source of a lot of complaints about Edelbrocks from people who can't be bothered to properly tune them.) When you leaned it out, the gas mileage improved a lot AND the horsepower went up across the rpm band. BTW, going to 8" springs delays the point at which the rods pop up and richen the mixture, so that was also a move that leaned out the engine.

An engine will almost always run OK rich, but go too lean -- above about 17:1 air/fuel ratio -- and the fire goes out. Which is what happens if the accelerator pump isn't set correctly. You open up the throttle and air rushes in, but the gas flow can't accelerate as quickly, so the A/FR goes above 17:1 and the fire goes out until the gas flow catches up, which causes a stumble when jumping on the throttle. The accel pump compensates by squirting raw fuel into the bores until the gas flow in the jets can accelerate up to the rate that matches the new air flow. In this case, by moving the accel pump to the innermost (shortest) hole on the lever, you richened the mixture for that brief time, and eliminated the stumble.

Horsepower is all about moving air through the engine. Fuel economy is all about making sure the right amount of gas for that amount of air is added, and not adding too much. Most people don't add too little, because the point where the fire goes out isn't a lot leaner than the optimum, so the errors are almost always to the too-rich side of things.

Anyway, congrats! Glad you got it sorted. That is very happy-making!
 

VAL

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So 3.73:1 with 35" tires is equivalent to 3.09:1 with stock 29" tires, plus a 700R4 with overdrive? Yeah, that's about the mileage you should be getting.

You're baffled because of a fundamental misunderstanding. Horsepower is not a function of how much gas you burn, but how much air you move through the engine. For a given amount of air, the maximum horsepower is at the correct mixture of gas. ADD GAS above the correct mixture and the horsepower and the mileage BOTH go DOWN, for two reasons. One is that the extra gas is not being burned, it's just wasted, killing your gas mileage. Two is that the additional gas displaces air that you could be moving through the engine, so the horsepower goes down as well.

This is why turbocharging and supercharging and nitrous add so much horsepower. Turbocharging and supercharging blow more air through the engine. Nitrous has more Oxygen atoms per molecule than air, so it is as if there were more air going through the engine. People don't blow GAS through the engine, they blow AIR through the engine. You need enough gas flow to keep up with the air at the proper ratio, but more gas alone makes things worse, not better.

Just some dumb numbers. Let's say you are moving fifteen parts of air per second and one of gas per second. That's about the right mixture. So you will get the horsepower associated with fifteen parts of air. Add gas, so you are running too rich, so that now you have two parts of gas per second. Well, the second part of gas won't burn, not enough air, so it's just wasted. But it's worse than that, because now you only have fourteen parts of air. The other part of air you could be moving is the wasted gas. So the horsepower goes down to what you would get with fourteen parts of air, not fifteen. So you are using more gas, and horsepower went down.

You were running way rich, because Edelbrocks are set up for a wide range of different engines, and our truck engines are a poor match to their factory jetting. (Which is also the source of a lot of complaints about Edelbrocks from people who can't be bothered to properly tune them.) When you leaned it out, the gas mileage improved a lot AND the horsepower went up across the rpm band. BTW, going to 8" springs delays the point at which the rods pop up and richen the mixture, so that was also a move that leaned out the engine.

An engine will almost always run OK rich, but go too lean -- above about 17:1 air/fuel ratio -- and the fire goes out. Which is what happens if the accelerator pump isn't set correctly. You open up the throttle and air rushes in, but the gas flow can't accelerate as quickly, so the A/FR goes above 17:1 and the fire goes out until the gas flow catches up, which causes a stumble when jumping on the throttle. The accel pump compensates by squirting raw fuel into the bores until the gas flow in the jets can accelerate up to the rate that matches the new air flow. In this case, by moving the accel pump to the innermost (shortest) hole on the lever, you richened the mixture for that brief time, and eliminated the stumble.

Horsepower is all about moving air through the engine. Fuel economy is all about making sure the right amount of gas for that amount of air is added, and not adding too much. Most people don't add too little, because the point where the fire goes out isn't a lot leaner than the optimum, so the errors are almost always to the too-rich side of things.

Anyway, congrats! Glad you got it sorted. That is very happy-making!

Back in 2012 when I hade the engine rebuilt, I had no idea the carb would need a tuning, and the shop that did the work never mentioned it to me. I've always relied on other people to make sure my trucks are running good. Its like they say, "if you want something done right, do gotta do it yourself".
 

rich weyand

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wamullins

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I tuned mine with an AFR meter. Here's the setup I have. It's probably close for you.

secondary metering jets: Edelbrock 1426, 0.095" (stock jet)
primary metering jets: Edelbrock 1425, 0.092"
metering rods: Edelbrock 1461, 0.065" cruise, 0.057" power
step-up springs: 8#

After installing an Edelbrock carb 1406 on my stock 305, I looked on here for some tips, I found this. Ordered everything from Summit on Wednesday, installed everything today. Truck runs great, I owe a thank you to you for doing the hard work and then posting the info on here. Thank you sir....
 

rich weyand

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After installing an Edelbrock carb 1406 on my stock 305, I looked on here for some tips, I found this. Ordered everything from Summit on Wednesday, installed everything today. Truck runs great, I owe a thank you to you for doing the hard work and then posting the info on here. Thank you sir....

De nada. Thanks for letting me know.

Curious also about what your gas mileage does.
 

VAL

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After installing an Edelbrock carb 1406 on my stock 305, I looked on here for some tips, I found this. Ordered everything from Summit on Wednesday, installed everything today. Truck runs great, I owe a thank you to you for doing the hard work and then posting the info on here. Thank you sir....

I concur, Rich is a bad ass!
 

Mikeyworks

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Sublime

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I'm confused, Val went with 95 primaries and 92 secondaries BUT Rich went with the opposite. is this a mis-type? I need to rebuild my 1405 and would love to give this a try

Rich posted on the first page "I tuned mine with an AFR meter. Here's the setup I have. It's probably close for you.

secondary metering jets: Edelbrock 1426, 0.095" (stock jet)
primary metering jets: Edelbrock 1425, 0.092"
metering rods: Edelbrock 1461, 0.065" cruise, 0.057" power
step-up springs: 8# "

Excellent. So leaning it out just a bit (98 to 95 primaries; 95 to 92 secondaries), cleaning it out, and a new accelerator pump and floats did the trick. Oh, and toss in the phenolic spacer to keep the carb from overheating and simplify starting when hot.

You might get even better mileage jumping the step-up springs from orange (5") to plain (8"). Easy thing to try.

Nice. Thanks for letting us know how it turned out.
 

86AZBurb

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I hope reviving this thread is ok as i ran into a similar issue with my 86 Burb with Crate 350 and edlebrock 1406. I was planning on following the advice given here as she does seem to be running rich and idling way too slow. She failed on CO at emissions 144/40 and the test tech gave me a pamphlet that recommended the rejet to proper jet size and check floats for the correct measurement. Well I have all the parts recommended by Rich, .92 jets, rebuild kit, 8"Hg spings. However i wanted to test the vacuum first. Unfortunately it seems to be bouncing between 5 and 10"Hg. There are also a bunch of components on the motor i am not sure what they are. See attached, any advice or wisdom would be much appreciated. I can't register it in my name until she can pass emissions, or I spend up to 450 in repairs and get the wavier. If you think i should rebuild the carb before tracing the vacuum issue, let me know. I also have some videos.
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Rusty Nail

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:waytogo:

Hay @rich weyand was just lurking about recently, let's see if we can roust him! He's a pretty good ol boy really..

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86AZBurb

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I think I got it figured out. However she still failed on CO. it did come down from 140 to 77, but that still 30 over what's allowed. Any idea's? spark plugs and wires? PCV valve?
 

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If you are only getting 8-10 in-hg at idle and it is bouncing around, you have a major mechanical issue with that engine. You need to run a compression test. Also, you should be reading vacuum from the manifold vacuum port on the front of the carb.
 

Bextreme04

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I had a similar reading when I had a broken valve spring and was only getting ~20psi of compression in one cylinder
 

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