Author Topic: Edelbrock 1406 adjusting Air Fuel Mixture  (Read 13785 times)

Offline 1979C20

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Edelbrock 1406 adjusting Air Fuel Mixture
« on: July 28, 2011, 11:58:46 AM »
I was wondering roughly how far out to turn the mixture screws to get about the right mixture on a 350, stock engine, no egr or other emissions equipment, stock exhaust and intake manifolds. My brother picked up his 77 with a brand new edelbrock on it and the guy said it needed to be adjusted. So, once we got a temp gauge on it and saw it was running at 130, I realized the mixture was low. Well, the mixture screws were all the way in! We backed them out a turn and now its running a lot better. About 170 deg and it has all 8 cylinders strong now. 6 and 7 were weak.
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline beastie_3

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Re: Edelbrock 1406 adjusting Air Fuel Mixture
« Reply #1 on: July 28, 2011, 12:07:32 PM »
They say to turn one in at a time until it starts running poorly, then turn it back out a half turn or so, then repeat for the other screw. Thats about it IIRC

Offline beastie_3

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Re: Edelbrock 1406 adjusting Air Fuel Mixture
« Reply #2 on: July 28, 2011, 12:08:15 PM »
you can download their manual online

Offline 1979C20

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Re: Edelbrock 1406 adjusting Air Fuel Mixture
« Reply #3 on: July 28, 2011, 12:11:01 PM »
Well, that doesnt help me much. When I backed them out 1 turn my idle shot up and I had to back it back off. It didnt run poorly. So, does anyone remember how far out your screws are? I need a base line to go off of and then I will fine tune it according to the plugs.
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline jaredts

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Re: Edelbrock 1406 adjusting Air Fuel Mixture
« Reply #4 on: July 28, 2011, 03:34:03 PM »
Your idle speed should jump up.  That tells you that you are currently too lean.  You adjust the screws for maximum rpm and then use the idle speed screw to lower the rpm back down, then repeat.  At the end they tell you to turn the screws back in just enough to lower the rpm by 20 or so.  Mine came set very close to where I ended up but I don't know where that was...1 1/2 turns out maybe?  That really doesn't tell you anything--you need to follow the procedure.  You can't use your plugs to set it as there are way too many other variables that affect plug condition/color than just the idle mixture.  Remember that's all they are for is mixture at idle.  The air fuel mixture in all other circuits are mainly recalibrated using different jets/metering rods/springs.  Here's the process:

1. Fully warm engine and ensure choke is fully open.
2. Air cleaner in place.
3. Set desired speed with the air screw.
4. Adjust the IMS on ONE side to get the maximum possible RPM. Do not go rich
beyond the maximum speed point.
5. If the above changed the idle speed more than 40 RPM, then readjust the speed.
6. Adjust the side OPPOSITE of that in Step 4 to get maximum RPM.
7. Reset the speed.
8. Carefully trim each IMS to again get the maximum idle RPM.
9. Go leaner just enough to get a 20 RPM drop in speed.
10. Reset the speed to the desired RPM.
11. This is a Lean-Best Idle Set. Setting richer than this will not improve idle quality or
performance, but could tend to foul plugs.

Offline reload

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Re: Edelbrock 1406 adjusting Air Fuel Mixture
« Reply #5 on: July 28, 2011, 03:44:21 PM »
I was wondering roughly how far out to turn the mixture screws to get about the right mixture on a 350, stock engine, no egr or other emissions equipment, stock exhaust and intake manifolds. My brother picked up his 77 with a brand new edelbrock on it and the guy said it needed to be adjusted. So, once we got a temp gauge on it and saw it was running at 130, I realized the mixture was low. Well, the mixture screws were all the way in! We backed them out a turn and now its running a lot better. About 170 deg and it has all 8 cylinders strong now. 6 and 7 were weak.

Running lean (screws all the way in) would make the engine run HOT.  Not cold.  Just my two-cents.

Offline 1979C20

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Re: Edelbrock 1406 adjusting Air Fuel Mixture
« Reply #6 on: July 28, 2011, 03:50:39 PM »
Well, your .02c holds no value! Because the more fuel in the chamber at idle the hotter the combustion. If the timing is too far retarded it will run hot. But, the less fuel in the chamber the less heat is produced. It was sitting at 135 with the idle screws all the way in. And at 170ish with the screws out a turn.
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline reload

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Re: Edelbrock 1406 adjusting Air Fuel Mixture
« Reply #7 on: July 28, 2011, 04:03:14 PM »
Well, your .02c holds no value! Because the more fuel in the chamber at idle the hotter the combustion. If the timing is too far retarded it will run hot. But, the less fuel in the chamber the less heat is produced. It was sitting at 135 with the idle screws all the way in. And at 170ish with the screws out a turn.

Actually you are wrong.  For someone about to open a shop, you should understand the basics.  How much do you understand about air/fuel ratios?

Offline 1979C20

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Re: Edelbrock 1406 adjusting Air Fuel Mixture
« Reply #8 on: July 28, 2011, 04:04:58 PM »
In this specific scenario, that is how it worked out. I dont know why.
1979 SCLB C20 Q-jet 350 SM465 14b F.F. 4.10 G80
1989 GMC Suburban V2500 TBI350 TH400 4in lift 35's 14b SF

Offline reload

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Re: Edelbrock 1406 adjusting Air Fuel Mixture
« Reply #9 on: July 28, 2011, 04:12:08 PM »
I understand.

I would go to Edelbrocks site, and download the 1406 owners manual. 

Here is a good video explaining the idle/air mixture adjustment.  Also on youtube are the actual videos Edelbrock includes with their carb's, you will have to hunt around a little for those. 
http://www.youtube.com/watch?v=EEeKYZS-Stg

Also, more fuel will cool the combustion.  Have you ever been around alcohol or meth running engines?  They run extremely cool, and one of the reasons is they can run so much more fuel. 

When you adjust the idle mixtures, you will have to re-adjust the idle. 

Online VileZambonie

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Re: Edelbrock 1406 adjusting Air Fuel Mixture
« Reply #10 on: July 28, 2011, 05:06:28 PM »
Well, your .02c holds no value! Because the more fuel in the chamber at idle the hotter the combustion. If the timing is too far retarded it will run hot. But, the less fuel in the chamber the less heat is produced. It was sitting at 135 with the idle screws all the way in. And at 170ish with the screws out a turn.

1979C20

Your comment is inappropriate. YOU are incorrect in your assumptions. For the record your idle mixture screws are for exactly what it says. Idle - Adjust them to attain the best idle quality and lowest possible emissions. This requires accurate timing, choke adjustment, idle speed etc. Use a vacuum gauge and an exhaust gas analyzer to set properly. Since you probably don't have the necessary equipment, set your timing, and attain the best idle quality that you can by adjusting them outward from home
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Offline reload

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Re: Edelbrock 1406 adjusting Air Fuel Mixture
« Reply #11 on: July 28, 2011, 05:20:19 PM »
Well, that doesnt help me much. When I backed them out 1 turn my idle shot up and I had to back it back off. It didnt run poorly. So, does anyone remember how far out your screws are? I need a base line to go off of and then I will fine tune it according to the plugs.

Back-stepping a little bit here, but bare with me. 

Now this is just my opinion, so keep that in mind.   But I would forget going off the plugs when trying to fine tune a street engine these days.  There is so much crap in fuel that wasn't there years ago, it's going to make a true reading almost impossible on pump gas.  I am in Nebraska, and we have a mandated 10% ethanol blend, some pumps will sell 89/90 un-blended, but it costs a lot more.  It's crap but its the way it is.  The EPA knows best, just ask them.

If you wanted to run some oxygenated race fuel, on a brand new set of plugs you could get some good results, but otherwise I think you are wasting your time and money. 

FWIW.

-Matt

 


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