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How does an acceleration pump work?

Episode #93 of ‘Fix my carb’: read at your own peril. You’ve been warned.

When I pull on the ‘plunger’ (what is the right word?) of the
acceleration pump the engine slows down.

I can’t find a description of how this part works. (I can find
a description of how the ‘auxiliary acceleration pump’ works, but
that’s different.)

Does it control fuel or air?

Is it pneumatic or electrical?

What sensor makes it move? Does it respond to temperature or pressure
or mixture…?

Find a picture of my carburetor here:

Carburetor of a Toyota 22R engine

'87 Toyota Pickup 22R engine manual

An accelerator pump is a mechanical (not electrical not pneumatic) device that squirts extra fuel into the carb to momentarily richen it to aid acceleration. It is usually a diaphragm or a plunger type device. It actuates when you open the throttle plate. A check valve allows gas flow into the pump but prevents it from returning to the float bowl so it exits into the carb thru a small orifice.

Whet you describe is a failed pump. The plunger should cause the engine to speed up a bit unless too much is going in, then it slows down.

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Think like an oil can squirting fuel instead of oil.

See my response to your “fast idle” thread.

My '89 Toyota 22R engine was a plunger (little piston) accelerator pump. Whereas Troll is working on an old carbed Toyota pickup, his is probably similar.