Need some carb help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

72gmcshorty · 04-16-2005, 08:37 PM

I was looking at my carb (edelbrock 4 barrel) and noticed something odd (to me at least). When looking at the carb from the top, The carb has two back bowls (i think thats what they're called) exposed. The plate in front that opens and closes moves. My question is, what makes this plate move? I don't see it connected to anything. I see that the throttle has a little set screw that just touches the mechanism for moving the plate but when you step on the gas it moves away from the throttle plate thing. Anyone explain how this works or have a good pic? Please? This part in the pic. This is NOT my carb, just showing the part that I don't see hooked up to anything else on my carb

70 shorty · 04-16-2005, 10:23 PM

First off, that is a Rochester Quadrajet, second the plate on top of the cirlced area is the choke plate. It should pop closed when you push the accelerator to the floor once before starting when cold. It should then open up gradually to vertical as it is in the picture. Once the vehicle is warm, and the plate is fully vertical, it shouldn't move.

**53burb** · 04-16-2005, 10:25 PM

That is the choke butterfly. If the choke is connected and operating correctly, that flap will close or partially close, limiting the amount of air intake, changing your air/fuel ratio. As the vehicle warms up, it opens, increasing the air intake and changing your air/fuel ratio. The adjustment is from the black cap just to the right of it(passenger side).

jhow66 · 04-16-2005, 10:46 PM

It is the choke plate. When engine is cold the choke thermostat (a coiled bymetal-2 differant metals-) contracts to close the choke plate. When engine is cold it needs a very rich mixture (more gas then air) to start. With choke plate closed it cuts off most of the air as you crank the engine. After engine starts the choke pull off (vacumn operated) opens the plate a little so that it can pull in more air to keep from flooding the engine with just gas and no air. With the choke plate in this postion the fast idle cam has steps on it that a screw rides against so as to hold throttle open at a faster speed until engine is warm enough to run slowly. As the hot air tube sends heated air to choke thermostat it uncoils and opens the plate to the position shown in your photo. (boy was that a lot of typing with one finger

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04-16-2005, 08:37 PM	#1
72gmcshorty Registered User Join Date: Jul 2001 Location: North Delta, British Columbia Posts: 1,344	Need some carb help I was looking at my carb (edelbrock 4 barrel) and noticed something odd (to me at least). When looking at the carb from the top, The carb has two back bowls (i think thats what they're called) exposed. The plate in front that opens and closes moves. My question is, what makes this plate move? I don't see it connected to anything. I see that the throttle has a little set screw that just touches the mechanism for moving the plate but when you step on the gas it moves away from the throttle plate thing. Anyone explain how this works or have a good pic? Please? This part in the pic. This is NOT my carb, just showing the part that I don't see hooked up to anything else on my carb Attached Images __________________ 1992 Gmc 2wd 1972 Chevy Blazer 2wd Last edited by 72gmcshorty; 04-16-2005 at 11:00 PM.

04-16-2005, 10:23 PM	#2
70 shorty Where's my beer? Join Date: Oct 2004 Location: Glen Allen, VA Posts: 1,772	First off, that is a Rochester Quadrajet, second the plate on top of the cirlced area is the choke plate. It should pop closed when you push the accelerator to the floor once before starting when cold. It should then open up gradually to vertical as it is in the picture. Once the vehicle is warm, and the plate is fully vertical, it shouldn't move. __________________ 70 C10, shortstep, .30 over 250,Hurst shifted 3 spd parts hauler. Holley 390, Clifford Intake, Header, ported cylinder head, unknown bigger cam. 79 Corvette L82, 4 spd, black, red interior, headers, flowmasters, and unkown bigger cam. '03 Grand Cherokee Laredo, 4.0 4x4 daily driver. 165K miles, and runs great '08 Tahoe LTZ 4x4 155K

04-16-2005, 10:46 PM	#4
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	It is the choke plate. When engine is cold the choke thermostat (a coiled bymetal-2 differant metals-) contracts to close the choke plate. When engine is cold it needs a very rich mixture (more gas then air) to start. With choke plate closed it cuts off most of the air as you crank the engine. After engine starts the choke pull off (vacumn operated) opens the plate a little so that it can pull in more air to keep from flooding the engine with just gas and no air. With the choke plate in this postion the fast idle cam has steps on it that a screw rides against so as to hold throttle open at a faster speed until engine is warm enough to run slowly. As the hot air tube sends heated air to choke thermostat it uncoils and opens the plate to the position shown in your photo. (boy was that a lot of typing with one finger ) Attached Images __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

04-16-2005, 10:25 PM	#3
53burb Senior Member Join Date: May 2004 Location: Queen Creek, AZ Posts: 1,007	That is the choke butterfly. If the choke is connected and operating correctly, that flap will close or partially close, limiting the amount of air intake, changing your air/fuel ratio. As the vehicle warms up, it opens, increasing the air intake and changing your air/fuel ratio. The adjustment is from the black cap just to the right of it(passenger side).



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