# How does an acceleration pump work?

**URL:** <https://community.cartalk.com/t/how-does-an-acceleration-pump-work/99951>\
**Category:** Maintenance/Repairs\
**Tags:** toyota, pickup\
**Created:** [February 16, 2017, 1:37am UTC](https://community.cartalk.com/t/how-does-an-acceleration-pump-work/99951 "2017-02-16T01:37:17Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![RandomTroll](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/randomtroll/32/12184_2.png) [@RandomTroll](https://community.cartalk.com/u/RandomTroll)\
**Post date:** [February 16, 2017, 1:37am UTC](https://community.cartalk.com/t/how-does-an-acceleration-pump-work/99951/1 "2017-02-16T01:37:17Z")

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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](http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/04/d6/c7/large/0900c1528004d6c7.gif)

'87 Toyota Pickup 22R engine manual

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**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\
**Post date:** [February 16, 2017, 2:36am UTC](https://community.cartalk.com/t/how-does-an-acceleration-pump-work/99951/2 "2017-02-16T02:36:57Z")

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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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**Author:** ![bing](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/bing/32/4619_2.png) [@bing](https://community.cartalk.com/u/bing)\
**Post date:** [February 16, 2017, 2:42am UTC](https://community.cartalk.com/t/how-does-an-acceleration-pump-work/99951/3 "2017-02-16T02:42:51Z")

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Think like an oil can squirting fuel instead of oil.

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**Author:** ![shanonia](https://avatars.discourse-cdn.com/v4/letter/s/9de053/32.png) [@shanonia](https://community.cartalk.com/u/shanonia)\
**Post date:** [February 16, 2017, 2:53am UTC](https://community.cartalk.com/t/how-does-an-acceleration-pump-work/99951/4 "2017-02-16T02:53:42Z")

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See my response to your “fast idle” thread.

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**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\
**Post date:** [February 16, 2017, 8:28pm UTC](https://community.cartalk.com/t/how-does-an-acceleration-pump-work/99951/5 "2017-02-16T20:28:54Z")

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> [@Mustangman](#):
>
> It is usually a diaphragm or a plunger type device.

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.