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Carb tuning help for a newbie

David Hawkins

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Aug 30, 2006
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50
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Mechanicsburg, PA
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1962 Ermine White Hardtop
As I continue to get deeper and deeper into our 62, I'm starting to realize how much I've forgotten about carburators. I've been a Fuel Injection guy for the last 20 years and haven't touched a carb since I stopped driving my 66 Corvair Monza with 2 1bbls.

My 62 has a Holley 4053 4bbl on it, which I think is WAY too much carb for the car (327, high lift cam, solid lifters), being a 780cfm carb according to everything I've read. The car has been pig rich since we got it and had some pretty healthy backfiring issues on the drive home from Carlisle.

I pulled the plugs (all 8 were black), set the point gap and tinkered with the carb yesterday. The mixture screws were about 4 turns out, so I turned them in and then backed them out about 3/4 turn. That helped with the heavy black smoke exiting the pipes.

I *think* from what I've read that this carb should be vacuum secondaries with an automatic divorced choke. If that's true, I think I'm missing some pieces and understand why the car was so rich - it has no choke thermostat and thus no choke...so the mixture had been turned up to compensate for the lack of a choke. If I'm right, there should be a bi-metal spring mounted to the manifold where the threaded hole is under the choke and it should be attached to the hole on the choke arm (both circled in my crude MS Paint picture).

All of that said...short of taking things apart and changing jets, what are my options for adjusting the mixture on this carburator? Just the two small screws on the front? Do they affect mixture across the board or just at idle? Can I buy just the choke spring and rod somewhere?

I'm planning to replace the carb, but would like to find the correct AFB 3296-S to do it rather than go through an intermediary carb on the way to the AFB.

Thanks for any advice - thanks to JohnZ for already answering a ton of my questions via searching this and the various Z28 forums!
 

Tom Bryant

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1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
Hi David,

Yes it's a vacuum secondary carb. That big diaphram on the side opens the secondaries. Your choke rod, thermostat and cover are missing. Without the choke hooked up or a spring holding the choke flap open it can suck closed during operation. This is probably part of your problem and most likely the cause of that black cloud following you. I ran one of these on my '67 with no choke at all with no problems. Hook a spring on that choke lever to hold it open until you can get the choke parts and you should have a good running carb. It may need a little warming up on cold starts but after that it should be fine. The choke pieces can be had from www.corvette-paragon.com .

As for it being too much carb for your 327, it may be at wide open throttle. Driving around normally it should run fine and give you good service until you can find that right AFB. 3/4 to about 1 1/2 is a good area for adjusting the idle mixture screws. Someone had them way too far out. Hook up a vacuum guage and adjust them for highest reading. Do one then the other. Then repeat again. Once you bring the engine up to a higher rpm than idle you aren't using the idle circuit any more so these have no effect on road manners. Then set idle speed to specs.

I wouldn't go messing with jets until you do this first and get that choke either hooked up or held wide open. More than likely the jets are pretty close to right unless someone really messed with the carb.

Tom
 

David Hawkins

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Joined
Aug 30, 2006
Messages
50
Location
Mechanicsburg, PA
Corvette
1962 Ermine White Hardtop
Thanks Tom. Does a divorced choke need a choke tube, or is the heat from the intake manifold the only thing that acts on the thermostatic coil?

I never thought of the choke plate flapping around...I'll get a spring on that puppy ASAP!
 

IH2LOSE

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May 24, 2001
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We Will All Meet Again
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1966,and a 1962 thats almost complete
Do you know this carb since new? the reason I ask Anytime I am trying to tune a holey I open it up to see if some one has plugged the power valve or if its an older holley to see if its blown.

Your idle adjustment are just there for idle once your off idle they are out of the circuit.

Make sure the car is in tune,then set them all the way in (softly you dont want to ruin the seat) I then mark the top of the screw with a daub of nail polish then come out 1.5 turns as a base line.

I hook up a vacuum gauge and adjust back and fourth ,side to side an 1/8th to a 1/4 turn at a time.I let the carb settle after each adjustment if I am out past 3 turns or all the way in and the car is not running good then I am looking for other thing that can effect it.

What plugs are you running ? what gap are you set at.

Look at the entire motors tune while your in there.

I have a real old book on holleys that taught me how to tune them. If I am going to help some one and they have a holley I always read it the night before as a refresher.

Good luck and keep us posted
 

IH2LOSE

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We Will All Meet Again
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1966,and a 1962 thats almost complete
I think you may have a hard toime getting the choke hooked up there with the fuel line.

I know allot of folks who wont run a choke because they are summer cars, But if your going to run a choke there are kits from holley to convert it over to an electric choke
 

David Hawkins

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Messages
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Location
Mechanicsburg, PA
Corvette
1962 Ermine White Hardtop
I haven't know the carb but for about 3 weeks. :)

The plugs are gapped to .035 and were newish Delco 45s. The points were newish also and I set their gap to .015 at the top of the distributor lobe. Static timing is 10BTDC. Everything on the tune-up side looked good (the point gaps were a little wide, but not terribly out of spec and the plugs ranged from .033-.038). I haven't had a chance to drive it since tinkering because they're tearing up my street for resurfacing...it does seem to idle and free rev better, though.

I zip tied the choke open last night. It's definitely not going to be a winter car, so I probably won't put a lot of effort into the choke.
 

Tom Bryant

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1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
David,

The divorced choke does not use a heat tube. Just the heat from the exhaust passage in the intake warms the therm. But if I'm correct, Corvettes didn't use the divorced choke until 1966 and AFBs (used 1962-1965 on 300 and 340 horse engines) all used the carb mounted choke and heat tube from the exhaust manifold. It looks to me like you have a newer intake on your car. This shouldn't effect the therm or cover but the rod length will have to be close to start with. Since you have the aluminum intake I'd order the rod for the high perf engines (350 & 365 horse). It should be the right one.

Paragon numbers: Cover 1714
Thermostat 1709K
Screw 1708
Rod W/clip 1838K

The reason I looked these up is because I need the same parts for my project. I just got the carb back from Bob Kunz and he told me to use choke parts for a 1966 300 horse with Holley. It's a 1966 Chevelle/Nova 300/327 carb. Since I'm using an Offenhauser manifold which is taller I need to get the longest rod I can and tweak it from there. Here is a picture of my setup. Very similar to yours except for the distance from the choke mounting to the choke lever on the carb.

Tom
 

Tom Bryant

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Edgerton, Ohio, United States
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1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
One other thing, My fuel fitting is on the opposite side of the carb so I don't have the interference that you do. You may be able to use a tubing bender and bend the line kit so it goes out horizonally from the carb. That would get it off of the therm pad and might swing it out far enough to clear the choke rod. The chrome plating will more than likely crack though. That may not be a issue since you are looking to replace this carb later anyhow.

Tom
 
Joined
Jan 1, 2002
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Location
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'67 Marina Blue Convertible
I don't know what intake manifold you have, but it doesn't appear to have the cast-in deep well to accommodate the remote choke thermostat, and the screw hole for it is in the wrong place.

Photo below is also a 4053 (on my '69 Z/28), with the stock remote choke and rod in place. The 4053 is WAY too much carb for either a 302 or a 327, but they were released for production only so the Trans-Am cars (which spent their life at WOT between 4000-8000 rpm) could use them. When I was having my 4053 restored, I ran a 600 Holley on the Z/28, and it was a MUCH more pleasant car to drive.

You'd probably be a lot happier with a Holley 1850 (600CFM) with an electric choke - better metering signal, crisper throttle response, and no "cobble" arrangements for a functioning choke.



:beer
 

David Hawkins

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Joined
Aug 30, 2006
Messages
50
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Mechanicsburg, PA
Corvette
1962 Ermine White Hardtop
How'd I know you were going to say that, John? :) (I read essentially the same thing in a post by you from 2001 on a Z28 forum).

Is the 1850 the same thing as the Holley 80145 that you recommended to the Camaro guys?

Would you recommend going this route over holding out for the proper AFB (although a 3296 appears to be pretty hard to come by...)?

Edit - the manifold is an Edelbrock...one of the many things that I plan to eventually replace.
 

David Hawkins

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Joined
Aug 30, 2006
Messages
50
Location
Mechanicsburg, PA
Corvette
1962 Ermine White Hardtop
Are the Carter AFBs date coded? I've found a place that has restored 3269s for $795 (seems kind of pricey, but if they're truly as rare as they're appearing to be I guess you pay for that rarity...). For that price, I want to be sure I get one that will be proper for my car.
 
Joined
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Messages
7,246
Location
Washington, Michigan
Corvette
'67 Marina Blue Convertible
The Corvette 3269S AFB used main body casting #0-1466 on very early cars, and #0-1481 on all the rest; all used air horn casting #6-1518. They're dated only on the foil tag under an air horn screw.

The #80145 I used on the Z/28 is a model 4150 that's visually identical to the 4053 (two metering blocks, dual-feed, center-hung floats, vacuum secondaries), but it's 600 CFM and has an electric choke.

The 1850 is a model 4160 (primary metering block, secondary metering plate) with a single fuel inlet, transfer tube, side-hung floats, and vacuum secondaries, and has been the Holley "universal replacement" carb for decades - looks almost identical to the 2818, 3367, and 3810 carbs used on '64-'67 Corvettes.

:beer
 

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