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Discussion Starter #1
So, I am done fooling with my 1403. Just can't get the idle circuit to work after a thorough cleaning and rebuild.


I want to get another Edelbrock for my '68 J code with a Shelby intake, HIPO type exhaust manifolds and mild cam. C4 auto. Want to get the Edelbrock so I do not have to mess with fuel lines or linkages


Should I stick with the 1403 for my small block as currently modified? Or would the 1406 be a better choice? I am not interested in squeezing out every last HP as I drive the car fairly gently. Open it up once in a while to"clean the carbon out", officer. It has plenty of power as it sits now.


I notice that the 1403 costs a little more than the 1406. Other than that, what might be the pros and cons of each.


Thanks.
 

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I would stick with the 1403. What are the symptoms at idle? When you state you can't get Idle circuit to work after cleaning etc. What is you vacuum at Idle?
The Pros?, you've already stated.
Not sure these are CONs, so much as they are differences.
1. As mentioned, more tuned for economy
2. It's has higher CFM
3. May need to be tuned via metering rod changes for optimum efficiency with your particular engine mods.

You state you are not interested in seeking out the last ounce of HP, while this may be true for you. you still need to tune any carb to work "happily" with any given engine. The only way to really know is to check the AFR at idle, mid-range, and WOT. It's just way it is.....
 

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I’m concerned that you can’t get it to idle right.
I’m even more concerned that a new Edelbrock carb may not fix the problem.
Like, maybe it’s not the carb?

I think 500cfm is best for your application.
If you really want a new Edelbrock carb you should consider getting one of the AVS series. They are a newer design with features that may improve your situation.
 

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I have a similar setup, but a T5 rather than a C4. ('72 302, Edelbrock performer 289 intake, mild cam, hi-po exhaust manifolds, T-5, Pertronix ignition) With my 1406, it had flat spots and stuttering with the default tune. It was set so lean it was not driveable. After setting it up with the springs/rods/jets from a 1405 default, it runs great.

I read that the 600 cfm is over kill for a 302 though. If I didn't love how it feels when I get on it so much, I would probably consider the 500 cfm. Reading the details on summit about the AVS series, I see it advertising addressing some of my negatives about the 1406 are part of it's design. That sounds like solid advice there too.

I do have a Holley 2bl 500cfm on my convertible with a 302, and it works great, but just doesn't have the get up the coupe has. Other changes too, but the get up and go is too exhilarating. Need more power.

If it were me, I would be going with the AVS2 1906.
 

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I don't think you should give up on your 1403. A good investment for tuning your carb is to install an AFR gauge. With it, you can see the AFR real time. I have the AEM model 30-0300 and with it I was able to tune my 1403.


Regarding the idle circuit, the basics are to ensure the carb is clean, timing is set, and you don't have any vacuum leaks. After these are checked, next back off idle speed screw until the throttle blades are fully closed (screw is not touching). Then turn the idle speed screw back in until it just makes contact and then add only 1/8th of a turn more to start. If you turn in the idle speed screw too much, the throttle blades will expose too much of the transfer slot adding fuel not metered by the idle mixture screws. Since you're having trouble adjusting the idle mixture, check that the idle speed screw is not exposing too much of the transfer slot.
 

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Discussion Starter #9
I would stick with the 1403. What are the symptoms at idle? When you state you can't get Idle circuit to work after cleaning etc. What is you vacuum at Idle?
The Pros?, you've already stated.
Not sure these are CONs, so much as they are differences.
1. As mentioned, more tuned for economy
2. It's has higher CFM
3. May need to be tuned via metering rod changes for optimum efficiency with your particular engine mods.

You state you are not interested in seeking out the last ounce of HP, while this may be true for you. you still need to tune any carb to work "happily" with any given engine. The only way to really know is to check the AFR at idle, mid-range, and WOT. It's just way it is.....
I just can't get it to stay running at anything under 600 rpm (not in drive). One mixture screw does virtually nothing. The other one gives best results at 4.5 turns out. Other than the idle issue, it performs great. At about 700 RPM, I get about 14 inches. At a steady 1,200 rpm i get a rock steady 21 inches.
 

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Discussion Starter #11
I’m concerned that you can’t get it to idle right.
I’m even more concerned that a new Edelbrock carb may not fix the problem.
Like, maybe it’s not the carb?

I think 500cfm is best for your application.
If you really want a new Edelbrock carb you should consider getting one of the AVS series. They are a newer design with features that may improve your situation.
I will check into that. What AVS would you recommend for my set-up? I thought the AVS series was more for higher performance. My Autolite 45 plugs have 400 miles on them and they still look brand new and a .035 gap. Dwell is right on with blue streak points and condenser also with 400 miles on them. Compression is within specs with no more than 5lb variance between cylinders. Have played with timing from 6 btdc (where I always had it) all the way to 12 btdc. Vacuum and mechanical advances are in specs and I have the vacuum advance hose on the correct (passenger side) port.



If all of a sudden I developed a vacuum leak within the stock bendix brake booster, could this be causing my problem? the power brakes are working fine though.
 

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I just can't get it to stay running at anything under 600 rpm (not in drive). One mixture screw does virtually nothing. The other one gives best results at 4.5 turns out. Other than the idle issue, it performs great. At about 700 RPM, I get about 14 inches. At a steady 1,200 rpm i get a rock steady 21 inches.
Yeah, it appears there is still blockage in the idle air circuit. Both screws should be "out" about the same, as you, probably already know.
I'm thinking you have your Dist. Vac connected to the "Timed Port" ? For optimum performance, should be connected to full vac port. With your Gauge attached to the "full" port, at approximately 600-800 RPMs, you might see a reading of approximately 16 - 18, depending on your cam events and overall engine health.
I would expect your "Drive" idle setting should be 600 with a slightly higher setting in Park/Neutral.

However first, you need to get the carb working as it should. You might look for a local shop with a "Sonic" cleaning parts bath.
 

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I had a 1406 on mine for 20 years and got tired of fooling with it trying to get it to run smoothly when at idle or not to have a dead spot accelerating out of a turn. I put on the original and best...an Autolite 4100. Aaaaand DONE.
 

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.

Where did you find the 4100? eBay?
That's correct. Got a 1.12 first, somebody local wanted it more than me, then I got a 1.08 and a rebuild kit for my 66.
 

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I'd bite the bullet and ditch the Edelbrock's in favor of a Summit M2008VS600. If you ask me, Vic putting his name on the Carter AFB/AVS was one of his stupider ideas.
 

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For what it's worth … a re-build of my original Holley did not solve the surging/flat spots I was suffering. I put on a 1906 and had Dan at the Mustang Barn recurve a new distributor with DuraSpark and all is good. As I changed three things at once, I can't place all (or even some) of the improvement on the carb.
Just my experience.
 

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For a stock 1968 302 I think 500CFM Eddy is the best bet. I've had both a 1406 and a 1403 on my 1968 J-code 302 stock engine. While you can tune both carbs to that engine it seems to me that the 1403 has a larger "sweet spot" for tuning and it also seems like the 1403 has slightly better throttle response (although that might be my imagination - both were pretty good). IMO, your options are...

(1) New 1403
(2) New 1406. If you can determine that the issue is with body of the carb and not the venturi boosters then if you buy a 1406 you can just try *both* the 1406 and 1403 venturi boosters and see which you like best.
(3) Buy a 1903 AVS2 500CFM. This has the annular discharge boosters that have gotten good reviews.
https://www.summitracing.com/parts/edl-s0004/overview/

Personally, if I were buying a new carb I would go with 1903.

Also - video on cleaning a carb idle ckt
 
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