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Discussion Starter · #1 ·
I am asking for clarification on how fuel moves through the cap of the accelerator pump. I made a crude photo to help. The little brass tube (#3) under the cap of the accelerator pump is blocked on my pump. When I spray carb cleaner through one of those micro-straws into the small brass tube (#3), no cleaner enters the hole, it sprays back. Neither does spray cleaner enter the hole on the rim (#2). Fluid sprayed into the rim hole (#2) sprays back also. The other rim hole (#1) goes to a hole under the cap (#5) and it is wide open. Piecing together what I can, it seems gas flows by gravity into hole 2 then fills the space below the diaphragm through either 3 or 4 (or both?). I can't tell on mine (since the passages are blocked). When the diaphragm is pressed downward, I assume gas is pumped through hole #5 up to the tube carrying a bit of gas to the two nozzles near the choke flaps. Is this correct? If it is, why there are two passages to fill the chamber below the diaphragm? (3 and 4). Thank you, and apologies for any redundancy. I have read similar posts but can't find an answer to my specific question. Either I was not patient enough or searched poorly.
 

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The diaphragm blocks off everything except holes 1 and 2. If you look at the other side of the cap you will find that hole 2 connects to the middle of the cap, hole 4. Under hole 4 there is a check valve I believe. Hole 1 has a passage which connects to hole 5. I suspect that fuel enters through hole 4 via hole 2 and the fuel is expelled through hole 5 via hole 1. Or it could be the other way around. I'm not sure of the function of hole 3.
 

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Discussion Starter · #3 ·
The diaphragm blocks off everything except holes 1 and 2. If you look at the other side of the cap you will find that hole 2 connects to the middle of the cap, hole 4. Under hole 4 there is a check valve I believe. Hole 1 has a passage which connects to hole 5. I suspect that fuel enters through hole 4 via hole 2 and the fuel is expelled through hole 5 via hole 1. Or it could be the other way around. I'm not sure of the function of hole 3.
Thanks, Mike.
I appreciate your insights. It is quite clear from the moldings on the outside of the cap that there is a connection between 2 and 4. Hole 2 sits under a hole in the float bowl and appears to drain by gravity, unless there is sufficient pressure in the float bowl to push gas through #2. I am thinking #4 has the square plug inside the round hole to atomize the incoming gas, but I can't imagine there is sufficient pressure to atomize it, but definitely let it trickle. Number 3 might be a base for a check valve to prevent gas from returning to float bowl through 2 when the pump is pressed?

I've been soaking it in alcohol for several days and still nothing. I'll wait some more time. I doubt there is a source for replacements other than to replace the entire carb.

REgards,

Eric
 

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...I am thinking #4 has the square plug inside the round hole to atomize the incoming gas,
I believe that the check valve is under the square plate in the round hole. The fuel will flow in through the area of the round hole not blocked by the square plate. When the accelerator pump shaft is operated the diaphragm applies pressure to the fuel and forces it out through hole 1 via 5. The check valve in hole 4 prevents fuel from going into that opening.

See this pic showing what is in hole 4, the check valve.
Accelerator pump cover missing part
 

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Discussion Starter · #5 ·
Agreed... fuel enters the chamber through the round hole with the square peg in it. It is sourced by hole 2. Hole 2 is gravity fed so I can't see why pressurized carb cleaner forced into 2 can't emerge easily from 4, unless there is an obstruction. I can imagine bad gas turning to varnish as being that blockage, but soaking in alcohol for a week has not softened it.

On can see evidence of how the channels were originally drilled into the casting. One hole for 4, one each for the 1-5 channel, one for 2, and one for 3. An additional one was drilled from the outside of the cap entering the side adjacent to the bottom of 2, penetrating 2 and moving to the bottom of 4. The hole from the outside is plugged with a soft metal. This channel allows fuel to move from 2 to 4. The mystery to me is in two parts. First, is there a gravity check ball that lifts as fuel enters the chamber below the diaphragm and then fall into place to block fuel from moving back to 2 when the plunger increases pressure in the chamber? This blockage would direct the fuel out 5 to 1. Second, what is the function of 3? It appears under high magnification that it has a brass bottom (at least mine does). Why is it a tube if it is not meant to be a passage?

Thanks for your expertise, Mike. I have seen that photo you posted before but it only adds questions. And it anyone else wants to chime in, please do.

Eric
 
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