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Discussion Starter #1
Ok, I've read for days about the idle circuit but cannot figure this one out.

I have a 396 engine. It had a 850dp on it but was too much carb for the 4k lb automatic truck that it was in. I took 2 different carbs and put on it from my other toys and the truck ran great and idled fine. So I decided to build this engine it's own carb. I started with a 80508S (750 vac sec). I added a rear metering block kit and a complete rebuild kit. The 396 has 8'' of vacuum at idle so I chose a 3.5pv. I put 72 mains in the front and 80's in the rear and a 31 squirter with purple spring. It runs great but won't idle! It will idle fine with 2 of my other carbs but not with this 80508. I tried a 4.5pv and a 6.5pv with no luck. It will only idle around 2k rpm with the 80508 carb. It will idle at 800rpm with the other 2 3310 carbs that have a rear metering block added.

Can anyone help me with this?
 

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Just a couple of quick checks....

If it has an electric choke it's not optional to leave it disconnected. It has to be connected to a switched 12V source.

That carb has a full manifold port hidden underneath the front right corner in addition to the one that is exposed on the back. If either is left unplugged or unused it's a big vacuum leak.
 

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Discussion Starter #4
Just a couple of quick checks....

If it has an electric choke it's not optional to leave it disconnected. It has to be connected to a switched 12V source.

That carb has a full manifold port hidden underneath the front right corner in addition to the one that is exposed on the back. If either is left unplugged or unused it's a big vacuum leak.
The ports are plugged. I will hook up the 12v choke and check this, thanks.

Check sec butterflys and are u 100% sure have the correct gaskets.
I thought all holley metering block gaskets and bowl gaskets were the same. Hmm, this may be my problem. I will check this, thank you
 

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The ports are plugged. I will hook up the 12v choke and check this, thanks.

That's probably part of it then. It's a thermal choke and if you hit the gas before you start it, the choke closes and the throttle goes to fast idle position. There is a little cam inside it that drops it every time you pat the gas to come off of fast idle. Without 12V hooked up, the choke cannot heat up and open.
 

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As you've deduced, the problem is in the carb somewhere.

If it will only idle at 2000 RPM, the throttle blades are cracked open pretty good, and the idle circuit is out of play.

There's a parts mis-match (someone above said wrong gasket(s), very possible), or serious blockage somewhere, float problem, etc.

Regardless, I'd do a tear-down of the carb and start all over with a new kit designed for your carb (always use a Holley kit).

Rebuilding a Holley only takes about an hour, and that's including the R&R of the carb.

Good luck!
 

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Discussion Starter #7 (Edited)
It's a thermal choke and if you hit the gas before you start it, the choke closes and the throttle goes to fast idle position. There is a little cam inside it that drops it every time you pat the gas to come off of fast idle. Without 12V hooked up, the choke cannot heat up and open.
I've got the choke turned where the butterfly stays open so I dont think this is the problem.

As you've deduced, the problem is in the carb somewhere.

If it will only idle at 2000 RPM, the throttle blades are cracked open pretty good, and the idle circuit is out of play.

There's a parts mis-match (someone above said wrong gasket(s), very possible), or serious blockage somewhere, float problem, etc.

Regardless, I'd do a tear-down of the carb and start all over with a new kit designed for your carb (always use a Holley kit).

Good luck!
I used a Holley rebuild kit for a 750vac sec carb. I've rebuilt dozens of carbs before. This one is just stumping me. I've been in it 3 times. I will re-check the part number of the rebuild kit and see if it was for a 80508. Thanks so far. When I find out what it was I will let yall know.

I used this kit: http://www.summitracing.com/parts/HLY-37-1542/?rtype=10
And this metering kit: http://www.summitracing.com/parts/HLY-34-13S/
 

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I clicked on your link that shows the Holley Rebuild Kit. I clicked the "Application" button on the same page and I didn't see your 80508 carb listed (or I'm blind,..entirely possible).

You sure that's the right kit for your carb?
 

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Discussion Starter #9
Update:

Sorry guys for the brainstorming question. I looked over all of the gaskets very closely and found the base gasket that I used was not the exact one that came off of the carb. It had 2 holes that didn't line up properly. My carb idles fine now. The "kit" came with 3 different base gaskets and I guess that I overlooked these tiny holes. Glad I found it, thanks to all of your help! :thumbsup:
 

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I knew about the base gasket..got caught like that some yrs back...and it was a tiny hole from memory on the front edge...
Ever since then I have always made my own gaskets...
And that way i can also 'blank off' and keep the ports I want.
 
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