Adjusting the Accelerator Pump
The pumps job is to shoot some fuel into the carb when the throttle is first opened. This is necessary because the normal circuits can’t add fuel fast enough during acceleration. It only functions through part of the throttle range, starting at idle. It does not go out of adjustment on its own and rarely needs replacement, except possibly after a carb rebuild. Symptoms of a non-functional or mis-adjusted accelerator pump are a bog or stall when you accelerate from idle in a normal or brisk manner.
This is the adjustment nut.
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The pump lever is actuated through this threaded rod, which is connected to the throttle linkage.
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Fully actuated
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Full throttle, you can see why the linkage is set up this way. After the pump has done it’s work, the lever stays fully compressed and the rod continues to move, compressing the spring, allowing the throttle to continue to open without hindrance.
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To check it, remove the air cleaner (the car does not need to be running, actually easier if it’s not running). Then while watching the nozzle, manually actuate the throttle. It should start to squirt as soon as the throttle is moved.
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photoshop in arrows and nomenclature
Nozzle pic
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Manually opening throttle pic
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squirting nozzle
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To adjust, turn the nut till it works properly. Turning it clockwise (tightening) delays the time when it squirts. And turning it counter-clockwise makes it actuate sooner. The trick to maximizing the a/p is to have it actuate at the proper time, without reducing the size of the pump shot. This is accomplished by backing off the pump arm nut till the lever no longer contacts the plunger, then gradually bringing it in till it squirts as soon as the throttle is opened. It’s a trial and error adjustment, as what sometimes looks perfect when the car isn’t running may still slightly bog and need a little tweak to make it perfect. Consequently, if you go to far, you start reducing the size of the pump shot, which may actually help your gas mileage if the carb stays running ok, without a flat spot during acceleration that would be caused by the pump shot ending before the main/transition circuits can catch up and “come in”. Yes I like run on sentences. :)
