1406 edelbrock tuning - Pontiac GTO Forum
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post #1 of 11 (permalink) Old 10-21-2019, 02:03 PM Thread Starter
 
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1406 edelbrock tuning

Just a reminder I have a 68 GTO with a 400, RPM intake, mild cam, MSD ignition. I've jumped through all the iginition hoops, including Lars advice.

I think I’ve determined I have a fuel issue and need the richen the primary rods and/or jets.

Here’s why. I tried the stiffest springs in the 1406 edelbrock kit with not much change. Out of desperation I doubled up the plain/natural springs with the stock chrome springs which stiffened them up substantially.

Well the chugging is greatly improved to an acceptable range.(It’s very subtle) I deduced a lean situation and figured I needed a thinner end metering rod and/or a larger primary jet?

The 1406 comes with .098 primary and a .070 X .047 metering rod. How much should I jump in rod size and/or primary jet?
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post #2 of 11 (permalink) Old 10-21-2019, 03:24 PM
 
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Might be a good time to switch over to a good, correctly built Q-jet. Plenty of good builders out there, as well as lots of good rebuild & tuning info available.

https://quadrajetpower.com

Also, a mild 400, with a mild cam, might run better with either an iron intake, or a Performer, rather than the RPM. Both are said to produce more low rpm power. The RPM is said to provide more top end power, especially on 455 & larger engines.
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post #3 of 11 (permalink) Old 10-21-2019, 05:12 PM Thread Starter
 
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Originally Posted by bigD View Post
Might be a good time to switch over to a good, correctly built Q-jet. Plenty of good builders out there, as well as lots of good rebuild & tuning info available.

https://quadrajetpower.com

Also, a mild 400, with a mild cam, might run better with either an iron intake, or a Performer, rather than the RPM. Both are said to produce more low rpm power. The RPM is said to provide more top end power, especially on 455 & larger engines.
Thanks BigD,

The cam is unknown and I'm assuming a "mild cam" with the familar lope at idle. The seller said it had a cam but no details.
I've worked so hard on tracking this down that for now I want to confirm that my theory is right?
The 400 is a low compression motor. 125-140psi
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post #4 of 11 (permalink) Old 10-22-2019, 08:15 AM
 
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According to the 1406 calibration chart the first step up would be a 1426 (.095) Main jet with a 1459 metering rod (.070 X .037). If you make this change, you should go back to the stock step-up springs and work from there, if needed.
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post #5 of 11 (permalink) Old 10-22-2019, 04:18 PM Thread Starter
 
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According to the 1406 calibration chart the first step up would be a 1426 (.095) Main jet with a 1459 metering rod (.070 X .037). If you make this change, you should go back to the stock step-up springs and work from there, if needed.
I'm not smart enough to decipher that chart, I think I missed something in school

I thought I could start with a pair of rods only and ordered from Summit .068 X .047. Please tell me if I'm not doing this right and I'll cancel the order and do as you said?

DO rods and jets have to be changed in pairs, can't do rods only or jets only? If someone could send me a link to purchase the next stage rich rods and jets, it would greatly be appreciated!!

Thanks!

Last edited by Red Skeleton; 10-22-2019 at 04:28 PM.
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post #6 of 11 (permalink) Old 10-22-2019, 06:25 PM
 
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The combo I gave you is 1 step richer in the power mode. If you want to changer only the rods, then 1458 (.075 X .037) will give you 2 steps richer in the power mode.
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post #7 of 11 (permalink) Old 10-22-2019, 06:31 PM Thread Starter
 
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The combo I gave you is 1 step richer in the power mode. If you want to changer only the rods, then 1458 (.075 X .037) will give you 2 steps richer in the power mode.
Is the power mode the same as slow cruise? I want to be clear as that's where my problem lies.
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post #8 of 11 (permalink) Old 10-22-2019, 08:00 PM
 
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In reading your original posting it seems that you are having problems as you are accelerating while cruising. By changing the springs it appears that you're trying to step up the rods quicker or at a higher vacuum reading. If that's true, then you're trying to gain power quicker. It appears that you're borderline with the factory setting, so I would go with my original suggestion. I'm running that carb on my '66 389 and I went with the first suggestion that I made to you, and it solved my lean problem using the factory suppled springs.

I hope that others running this carb might tell you of their experiences.
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post #9 of 11 (permalink) Old 10-23-2019, 05:27 PM
 
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I have the same carb and I can tell you that replacing the Performer RPM intake with the regular Performer made quite a difference in my 400, also with a ‘mild’ can that I have no ability to spec without a tear down.
I am still not happy with the 1406 though so I am going to have my factory original Carter Quadrajet rebuilt over the winter.


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post #10 of 11 (permalink) Old 11-08-2019, 12:51 AM Thread Starter
 
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Thanks for all your help guys! Definitely a metering rod issue. I just couldn't keep Lars' mantra out of my head "90 percent of carb problems are ignition problems". I've learned a lot from him and the fellow that sold me new rods. I highly recommend Jim who sells carb stuff on ebay https://www.ebay.com/itm/281496596883

I hope this helps someone else too.
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