How does the accelerator pump piston work in a Zenith?

dang

dang

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I've had my Zenith carbs apart quite a few times and still can't understand how the piston works for the accelerator pump. I get the concept of compressing a fluid in a cylinder and pushing it through an orifice, but I don't get how the assembly works together. Since it's not attached to anything, is the bottom "seal" more like a plug and is stationary while the top moves up and down? If the entire assembly moved down how would it come back up on it's own, float? I think I'm missing something simple here.

accel piston.jpg
 
Yes the seal fits snugly down in the bottom of the well and a lever presses the plunger down from above. Be very careful inserting the pumps into the carb as the seals can tear easily, rendering the pump useless, amhik. Pay very close attention to the seal as you install - don't force it, perhaps lube it. The seal stays put and the top moves. There are fuel inlet and outlet holes in the well.
 
These are buried in the stack of pancakes that make up the carb, easy to get to in ten minutes of work. Hitting the gas pedal gives an extra squirt of gas into the throat of the carb. On our 2800 these were original and no gas would squirt, Carl N told me to look in the throat to check. Originally they had a leather cup/seal, now it is rubber. When these don’t work, it is hard to accelerate without giving the car too much gas. I always had to use about 2000 rpm to get moving smoothly, now it is fixed and I can idle away if I choose.
 
Stevehose said:
Yes the seal fits snugly down in the bottom of the well and a lever presses the plunger down from above. Be very careful inserting the pumps into the carb as the seals can tear easily, rendering the pump useless, amhik. Pay very close attention to the seal as you install - don't force it, perhaps lube it. The seal stays put and the top moves. There are fuel inlet and outlet holes in the well.
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Yeah, it seemed strange that it would only go part way down the cylinder and then tighten up. The cylinder looks slightly tapered, not sure, but I guess that plays into it. I still can't understand why they did it that way. I'm sure there's a good reason but it's beyond me.
 
HB Chris said:
They make a huge difference, and no prostate check required.
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I found some ignition problems and narrowing it down to a few things now. The accelerator pumps are definitely on the list of things to improve.
 
Making sure both Carbs ‘tip in’ at the exact same time makes a big difference too. Steve posted a tutorial on syncing them as well with a Syncrometer.
 
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