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72 Chevelle Carb Problem

 
agraff3
I love my Chevy Chevette!
Posts: 3
Joined: 05/10
Posted: 05/04/10 08:55 PM

My father has a 72 chevelle malibu, 350 bored over, with a NEW 650cfm holley carb.
After recently purchasing the new carb, he installed the carb and followed directions i printed out for him for this website, to help setup his new carb. (Idle mixture)
The new electric choke works fine. After the choke releases, the car runs rough for approximately a few minutes, and dies out as if it is being too far leaned out. BUT THE MAIN PROBLEM IS THIS:

After the car chokes out, the carb continues and dumps fuel down the carb and floods the carb. Even after it shut itself off. After referring to a friend, he mentioned that he float level might be screwed up, but the carb doesn't have a float level adjustment...so we are at a stand still.

Anything to help, would be great. I'm sorry if this is very general, but its a weird situation and im not a carb expert. Its a brand new carb and we haven't had this problem before.

If i can provide any more details, i will gladly add to this
Thank you sincerely.  

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garyc945
I love my Chevy Chevette!
Posts: 2
Joined: 05/10
Posted: 05/07/10 08:36 AM

How to Tune a Holley 650 Carburetor
Contributor
By Don Bowman, eHow Contributing Writer
Article Rating:  (1 Ratings)
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Holley carburetors are extremely popular for their ease of adjustability and lack of moving parts. They contain two float bowls--one for the primaries and one for the secondaries. The float bowls have observation holes for outside adjustment of the fuel level. There are two replaceable jets on either side and a vacuum-operated power valve located in the primary side. On a 650cfm carburetor such as this, there are two idle mixture screws--one on either side of the carburetor, and an idle adjustment on the linkage. The accelerator pump is also adjustable and replaceable with different sizes to accommodate different cams. The vacuum-operated secondaries are adjustable with different strength springs.
Difficulty: Moderately ChallengingInstructionsThings You'll Need:
Set of ¼-inch drive sockets
¼-inch Drive ratchet
Flat head screwdriver
Phillips screwdriver
5/8-inch Wrench
Tachometer
Step 1Remove the air cleaner. Step on the accelerator pedal slightly. Observe the choke on the carburetor. The choke should be closed after stepping on the accelerator of a cold engine.

Step 2Start the vehicle and return to observe the operation of the choke and fast idle cam. The engine rpm should be around 1,500 rpm. The choke should start to open within two minutes as the engine warms up. With a tap on the accelerator pedal or on the throttle linkage of the carburetor, the rpm should drop to idle.

Step 3If the choke fails to close all the way or open all the way, use the Phillips screwdriver to loosen the screws on the black choke spring housing and turn the housing to adjust as needed.

Step 4Shut the engine off and remove the large plugs on the passenger side of the carburetor. If fuel is level with the bottom of the hole, it is correct. If the level is other than normal, adjustment can be made at the top of each float bowl. There is a common lock screw on top of a 5/8-inch nut.

Step 5Loosen the screw with a common screwdriver and turn the nut with a 5/8-inch wrench until the desired level is achieved. Lock the nut down with the screw. If the fuel level was too high, turn the nut clockwise, and conversely for too low. If the fuel level is too high, lower the fuel level, install the sight plug, start the engine and shut it down and recheck the level. Do not attempt to set the level with the engine running because the fuel pressure will spray fuel from the adjusting nut.

Step 6Hook up the tachometer and start the engine. Adjust the mixture screw on the driver's side first. Turn the screw to the right until the engine rpm begins to drop. Turn the screw to the left until the highest rpm is achieved and the rpm remains stable, then turn it to the right one quarter turn. Repeat the process on the opposite side and then repeat the process on both sides one more time.

Step 7Adjust the accelerator pump to begin operation when the throttle linkage has moved one-quarter inch. Do this by adjusting the nut on the bottom of the spring that touches the pump handle on the driver's side front of the carburetor.

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Tips & Warnings
Adjusting the primary or secondary jets for high performance reasons is a simple matter of removing the four screws in each float bowl and removing the bowl to expose the jets. The jets have a size inscribed on them for identification. Unscrew the old jets and screw the new jets in place, then replace the float bowls. Replacing the accelerator pump for performance reasons is simply a matter of removing them with the use of a Phillips  

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garyc945
I love my Chevy Chevette!
Posts: 2
Joined: 05/10
Posted: 05/07/10 08:36 AM

Hope this helps  

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agraff3
I love my Chevy Chevette!
Posts: 3
Joined: 05/10
Posted: 05/07/10 06:45 PM

We adjusted the mixture, but it still dumps fuel after shut off  Frown  

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idrivejunk
I mow my lawn and find Chevys
Posts: 5119
Joined: 12/09
Posted: 05/07/10 07:38 PM

Sounds like the float is stuck. If it won't unstick by lightly tapping the carb bowl, you need to take it apart and find the problem or unstick it. Very small debris can cause this.  
idrivejunk

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