Edelbrock 1406 failed emissions

[Georgeb]

Well, I was worried I had a Crack, turns out them bolt holes go all the way through the top half of the carb. I got in there and took a pic, man what a relief. I'm guessing the gasket is is toast.

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Sorry to cause panic. Glad it's just a gasket!

 

[rich weyand]

Those are the standard jets and rods, so they are probably the stock 5" springs.

The issue with the springs is that these engines pull so much vacuum, you are always in power mode with 5" springs. I stretched the 8" springs by 1/4" to get them to more like 9" springs. The springs should be half of your idle vacuum. So with an idle vacuum of 16" or more, you should use 8" springs.

Here's the thing. A lot of people don't calibrate carbs the way they should. If the carb is running on the raw edge of lean all the time, you can burn valves. So the Edelbrock carbs are delivered rich as hell so that no matter what engine someone puts them on, they won't burn it up.

Your plan is backwards. Leave the .095 jets in the secondaries or you will run lean at WOT. That's not good. And you will still be rich at idle, cruise, and half-power. Put the .092 jets in the primaries, and then go to the 65/57 rods. That will lean the carb out enough for the high vacuum signal it gets from these truck engines.

When you lean it out, since a lean mixture burns slower, you can also put in more advance. I am running 16-17 degrees BTDC with stock HEI and no problems. More advance gives a longer burn time and also helps with emissions.

 

[VAL]

Those are the standard jets and rods, so they are probably the stock 5" springs.

The issue with the springs is that these engines pull so much vacuum, you are always in power mode with 5" springs. I stretched the 8" springs by 1/4" to get them to more like 9" springs. The springs should be half of your idle vacuum. So with an idle vacuum of 16" or more, you should use 8" springs.

Here's the thing. A lot of people don't calibrate carbs the way they should. If the carb is running on the raw edge of lean all the time, you can burn valves. So the Edelbrock carbs are delivered rich as hell so that no matter what engine someone puts them on, they won't burn it up.

Your plan is backwards. Leave the .095 jets in the secondaries or you will run lean at WOT. That's not good. And you will still be rich at idle, cruise, and half-power. Put the .092 jets in the primaries, and then go to the 65/57 rods. That will lean the carb out enough for the high vacuum signal it gets from these truck engines.

When you lean it out, since a lean mixture burns slower, you can also put in more advance. I am running 16-17 degrees BTDC with stock HEI and no problems. More advance gives a longer burn time and also helps with emissions.

I see the reasoning in that, when you say to put the 92 primary and leave the 95 secondary jets where they are. But what the reasoning behind the factory 98 primary and 95 secondary. I'm trying to figure out why the primaries are larger than the secondary from the factory.

 

[rich weyand]

They want the mixture rich across the board for people who don't tune the carb, so they don't burn up their valves and blame the carb. Also, our truck engines have very high vacuum compared to high-compression/high-overlap engines. So they are going to run richer on the same settings.

There is no time when you are running on the secondaries alone, you are either running on the primaries alone, or the primaries and the secondaries together. Consider the throttle opening range of each set of barrels, where - is the primaries and = is both the primaries and secondaries:

Throttle low -----> throttle high
---------------============

So making the primaries rich makes the mixture rich across the board. So the primaries are rich from the factory, while the addition the secondaries give is about right.

By taking the primaries down to .092, you lean out the mixture over the entire throttle range, not just when the secondaries are in, and that's what you in particular need to do to get your emissions in line.

 

[rich weyand]

One additional note. The Carter carb (the Edelbrock's origins) was a production carb. The auto manufacturers did not test and tune each engine. They came up with a set of settings that worked for a prototype, and then tuned all of those cars the same on the production line. Same rods, same jets, same ignition timing.

That's why I think my carb setup, which I got with a lot of tuning work with a very nice A/FR meter, will probably just plug and play on your (very similar) truck.

And it surprised the hell out of me how lean I had to go to get the mixture numbers down to where they should be. That's because of the high vacuum of these engines.

 

[Camar068]

Good info Rich, thx.

 

[VAL]

One additional note. The Carter carb (the Edelbrock's origins) was a production carb. The auto manufacturers did not test and tune each engine. They came up with a set of settings that worked for a prototype, and then tuned all of those cars the same on the production line. Same rods, same jets, same ignition timing.

That's why I think my carb setup, which I got with a lot of tuning work with a very nice A/FR meter, will probably just plug and play on your (very similar) truck.

And it surprised the hell out of me how lean I had to go to get the mixture numbers down to where they should be. That's because of the high vacuum of these engines.

Well Sir, that makes alot of sense. I'm gonna do what you recommended. Thanks Rich.

 

[Georgeb]

Rich makes tuning fun!

 

[rich weyand]

Well Sir, that makes alot of sense. I'm gonna do what you recommended. Thanks Rich.

Let me know how it works out. There are some options I'm aware of (like I switch to 062/052 rods in the winter for a richer mixture -- probably not an issue in Tucson), and I'll try to help if that doesn't get you where you need to be. If you quote one of my answers above in your update, I'll get an email notice and won't miss your update.

 

[VAL]

Let me know how it works out. There are some options I'm aware of (like I switch to 062/052 rods in the winter for a richer mixture -- probably not an issue in Tucson), and I'll try to help if that doesn't get you where you need to be. If you quote one of my answers above in your update, I'll get an email notice and won't miss your update.

Hey Rich, I just got my kit this morning, earlier than expected. I just put the 92 jets in the primaries, will it still be ok with the elevation here in Arizona?

 

[rich weyand]

Yeah, use the .092s. You might want to start with the 62/52 rods, though.

 

[rich weyand]

Yeah, use the .092s. You might want to start with the 62/52 rods, though.

Wait a minute. That's backwards.

At higher altitude, you have fewer air molecules per volume, so you need LESS gas, not more.

Yeah, start with the 092 jets and 65/57 rods. We might be able to go a touch bigger on the rods to lean it out, like the 70/57. If you have to lean it out more than that, you will need to go to a still smaller jet, like the 089, 086 or 083, because the rods only go so big, and you'll have to get back into their range.

 

[VAL]

Wait a minute. That's backwards.

At higher altitude, you have fewer air molecules per volume, so you need LESS gas, not more.

Yeah, start with the 092 jets and 65/57 rods. We might be able to go a touch bigger on the rods to lean it out, like the 70/57. If you have to lean it out more than that, you will need to go to a still smaller jet, like the 089, 086 or 083, because the rods only go so big, and you'll have to get back into their range.

So it's 92 primaries, and 95 secondaries?. According to edelbrock, the 7547 rods I have, are the largest size they come in.

 

[rich weyand]

So it's 92 primaries, and 95 secondaries?. According to edelbrock, the 7547 rods I have, are the largest size they come in.

Yeah, and with 092 jets, those will be too lean in cruise and too rich in power.

 

[VAL]

Finally got into the carb, after seeing what was in there, I'm surprised it ran at all.

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The discoloration of the floats, I'm guessing, is from boiling fuel?