Rear carb/front carb

[Bird 426]

I have the Edelbrock #7524 intake and two Edelbrock #1405 carbs on my Hemi. When I got this car, the other owner was running around on the front carb primary. I've been through the engine and was going to run on the rear carb. It has been suggested by another member here that because of the single plane manifold, that I might want to run on both front and rear primaries. Is someone else here running a similar set up? This is a street car.

 

[Geoff 2]

I would just run on the rear carb primaries. They are about as centrally located as you can get with that intake & give you the best A/F distribution for idle & cruise.

 

[Bird 426]

That's my hope, will keep a close eye on the plug color.

 

[71RRHI]

I don't have a Hemi, but I have a 440 with dual holley carbs. I have played around with the settings, I find running on the rear carb primaries, with progressive linkage the best. If I try and run of both carbs primaries, idle and and low speed cruise is too rich

 

[lewtot184]

Not a hemi. Ch28 with two 1407's. I use the rear carb as a primary. Basically set up throttle linkage like a street hemi. Drives very nicely. The smaller 1405 may be fine with straight linkage. Try it both ways.

 

[dvw]

I don't have a Hemi, but I have a 440 with dual holley carbs. I have played around with the settings, I find running on the rear carb primaries, with progressive linkage the best. If I try and run of both carbs primaries, idle and and low speed cruise is too rich

Why would running both carbs have any effect on idle? It idles on both regardless of linkage. We’ve run all our dual Eddys together, not progressive. That’s been 5 different combos.
Doug

 

[Bird 426]

I can try it both ways to see where it's happy. Bought this with the #1405's, wondering if I need larger carbs like the #1407's. Or put my wall hanger set on, they would be large enough!

 

[lewtot184]

I had a pair of 600's on the engine for quite a few years. They were ok and reliable, but i didn't like the way they cruised above 60mph. The 750's are much better cruisers and performers.

 

[Bird 426]

Thanks guys. Will see how this set up goes. May start it the end of next week. We're supposed to get a snow storm here tomorrow night.

 

[71RRHI]

Why would running both carbs have any effect on idle? It idles on both regardless of linkage. We’ve run all our dual Eddys together, not progressive. That’s been 5 different combos.
Doug

Maybe I'm not describing it right. Never had dual quad's before, and only know how to adjust carbs from what I read, and try. I have the idle air screws adjusted only on the rear carb. And idle speed screw only adjusted on the rear carb. The front carb idle air screws are all the way in, and the idle speed screw is backed all the way out. Might night be right, but my car responds best with this setting.

 

[Geoff 2]

Edel carbs do not have idle air screws.

 

[Bird 426]

I'm thinking that the front carb contributes, just like a 6-pack. I would adjust the air/fuel adj screws on the front carb. Will find out.
So what are those two screws on the front of the carb base?

 

[lewtot184]

I treat all four primary barrels the same. The engine idles off all four barrels and should be adjusted as such. Smog street hemis didn't have adjusters for idle on the front carb but still had an idle circut. If the carb has mixture screws use them.

 

[dvw]

An Eddy carb is like most carbs. 2 mixture screws and a primary idle speed screw. Treat them the same as you would adjusting one carb. All screws out equally. With 2 carbs the air draw is half. So speed settings won’t require much opening. Won’t need the mixture screws out very far either. Likely one turn +/- . We’ve had stuff with cams up to 285@.050” idle fine with a pair of stock Eddy carbs.
Doug

 

[Bird 426]

Will let you know particulars after start.
Thank again! I have my answers.

 

[Runcharger]

I set idle on both carbs. I like running both 1-1 anyway. But even if running progressive I like to have both idle circuits working.

 

[AR67GTX]

My 66 Hemi with correct model Carters is currently set to idle on both carbs. Not sure why they would have provided an adjustable idle metering circuit on the front carb if that wasn’t the intent.

 

[Dragon Slayer]

I treat all four primary barrels the same. The engine idles off all four barrels and should be adjusted as such. Smog street hemis didn't have adjusters for idle on the front carb but still had an idle circut. If the carb has mixture screws use them.

Not true. All 66-71 Hemi have idle adjust screws front and rear. 66-67 are air valve type. 68-71 Front carbs have hidden idle mixture screws, but they do have idle screws. Remove the lead plug and you gain access to the hidden idle mixture screw.

 

[lewtot184]

Not true. All 66-71 Hemi have idle adjust screws front and rear. 66-67 are air valve type. 68-71 Front carbs have hidden idle mixture screws, but they do have idle screws. Remove the lead plug and you gain access to the hidden idle mixture screw.

I've never worked on all of them but the '69 my brother had didn't have external mixture screws on the front carb.

 

[Geoff 2]

The info in post #18 tells me that Chrys was not happy with the idle system....because they kept changing it. You only do that if you are trying to make it better.