carb issue
Thread Starter
Burning Brakes
Joined: Dec 2005
Posts: 1,179
Likes: 100
From: cranford nj
carb issue
I have a stock 71 with a 350 and a quad carb, when I get on it it bogs i can pedal thru it but would like it to kick in like it should. I think it is the accelerator pump how can i adjust it. Thanks in advance.
Melting Slicks
Joined: Mar 2006
Posts: 2,465
Likes: 0
From: Orange Park Fl
The two most common causes of the Quadrabog are the accelerator pump plunger deteriorating and the secondary air valve adjustment.
With the engine off, take off the air cleaner and look down the primary bores of the carb and pull the throttle linkage. You should see two solid streams of fuel go into the bores. If there is no fuel, or if it sputteres out weakly, buy a carb kit and replace the plunger seal.
The fix for the air valve is non-invasive. Look on the passenger side of the carb's secondaries. the Butterfly on top of the secondaries is the air valve and if it is set too loose, the carb will bog as the secondaries kick in. To adjust, you hold a small flat head screwdriver in the slot on the end of the butterfly's shaft as you loosen an allen screw that holds it from moving (the allen screw points up from under the passenger side end of the shaft). You want to adjust it to where the butterfly shuts, then 3/4 of a turn farther. Hold it in place with the screwdriver as you retighten the allen screw to lock it in place.
God bless, Sensei
With the engine off, take off the air cleaner and look down the primary bores of the carb and pull the throttle linkage. You should see two solid streams of fuel go into the bores. If there is no fuel, or if it sputteres out weakly, buy a carb kit and replace the plunger seal.
The fix for the air valve is non-invasive. Look on the passenger side of the carb's secondaries. the Butterfly on top of the secondaries is the air valve and if it is set too loose, the carb will bog as the secondaries kick in. To adjust, you hold a small flat head screwdriver in the slot on the end of the butterfly's shaft as you loosen an allen screw that holds it from moving (the allen screw points up from under the passenger side end of the shaft). You want to adjust it to where the butterfly shuts, then 3/4 of a turn farther. Hold it in place with the screwdriver as you retighten the allen screw to lock it in place.
God bless, Sensei
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 98
From: Ontario
The two most common causes of the Quadrabog are the accelerator pump plunger deteriorating and the secondary air valve adjustment.
With the engine off, take off the air cleaner and look down the primary bores of the carb and pull the throttle linkage. You should see two solid streams of fuel go into the bores. If there is no fuel, or if it sputteres out weakly, buy a carb kit and replace the plunger seal.
The fix for the air valve is non-invasive. Look on the passenger side of the carb's secondaries. the Butterfly on top of the secondaries is the air valve and if it is set too loose, the carb will bog as the secondaries kick in. To adjust, you hold a small flat head screwdriver in the slot on the end of the butterfly's shaft as you loosen an allen screw that holds it from moving (the allen screw points up from under the passenger side end of the shaft). You want to adjust it to where the butterfly shuts, then 3/4 of a turn farther. Hold it in place with the screwdriver as you retighten the allen screw to lock it in place.
God bless, Sensei
With the engine off, take off the air cleaner and look down the primary bores of the carb and pull the throttle linkage. You should see two solid streams of fuel go into the bores. If there is no fuel, or if it sputteres out weakly, buy a carb kit and replace the plunger seal.
The fix for the air valve is non-invasive. Look on the passenger side of the carb's secondaries. the Butterfly on top of the secondaries is the air valve and if it is set too loose, the carb will bog as the secondaries kick in. To adjust, you hold a small flat head screwdriver in the slot on the end of the butterfly's shaft as you loosen an allen screw that holds it from moving (the allen screw points up from under the passenger side end of the shaft). You want to adjust it to where the butterfly shuts, then 3/4 of a turn farther. Hold it in place with the screwdriver as you retighten the allen screw to lock it in place.
God bless, Sensei
Race Director
Joined: Apr 2003
Posts: 19,347
Likes: 654
From: Tampa, Florida
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 98
From: Ontario
Is that just at WOT or would it occur at more modest acceleration speeds as well? I ask the question because I have a mild case of the infamous off-idle stumble and although I have read the various papers on the subject, I am not sure what the remedy is. This stumble occurs very briefly on moving off from a stop sign or red light. The accelerator pump seems OK: it squirts and there is no slack between the actuating lever and the pump head. The gas pedal is a bit loosey-goosey suggesting a stretched throttle cable that on a 1974 is unfortunately not adjustable.
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Racer
Joined: Nov 2004
Posts: 485
Likes: 1
From: Oakville ON
Is that just at WOT or would it occur at more modest acceleration speeds as well? I ask the question because I have a mild case of the infamous off-idle stumble and although I have read the various papers on the subject, I am not sure what the remedy is. This stumble occurs very briefly on moving off from a stop sign or red light. The accelerator pump seems OK: it squirts and there is no slack between the actuating lever and the pump head. The gas pedal is a bit loosey-goosey suggesting a stretched throttle cable that on a 1974 is unfortunately not adjustable.
"The accelerator pump seems OK: it squirts and there is no slack between the actuating lever and the pump head."
Be sure the pump starts to squirt AS SOON AS the throttle is opened a bit. If the pump or the pump lever is set too high, the initial pump movement may not actually pump any gas and you get a lean stumble.
