Working on carb again...Little help Pic inside

[powerslave]

So I just rebuilt these 717 95 xp carbs. Didn't do pop off, but am now, bought a tester. This mag carb had fuel in it but looks like this plastic piece was preventing the fuel from getting to pto carb which is the one that was not getting fuel. Is this clear plastic piece supposed to be in here? The cover was bone dry like this clear plastic was preventing the fuel from getting to pto carb.

 

[mikidymac]

I am sure someone will post a diagram but the picture is correct. The clear plastic cover is the actual diaphragm that moves the fuel in and out of the fuel pump and the small plastic discs are the check valves to make the fuel move in and out.

The hose that connects to the chamber that covers this clear plastic sheet should go the your pulse line to the side of the crankcase not the other carb.

If you have twin carbs the one with the fuel pump should have 4 fittings and the carb usually has arrows cast into the fuel pump showing flow direction.
1. Is the line from the fuel tank into the carb.
2. Is a pulse line that operates the fuel pump.
3. Is a pressure feed from the pump to the other carb.
4. Is a return to the tank.

Carb 2 has 2 fittings.
1. Fuel in from the other carb.
2. Return to the tank (usually Wyed to the other carb).

 

[powerslave]

But the cover on that carb was dry. No fuel on it. Dosent fuel need to go out of that? or is it just air (vacuum)?

 

[mikidymac]

The cover is just for the vacuum and pressure pulses from the crankcase. The fitting on the cover goes to the side of the block fitting. The pulses move that clear plastic cover in and out pumping fuel into and out of the chamber you can see with fuel in it in your picture and those little clear discs are check valves that let the fuel in from the tank then stop it from flowing out back to the tank.

 

[powerslave]

OK, cool. Guess I need to perform my pop off test and replace the check valves.

The cover is just for the vacuum and pressure pulses from the crankcase. The fitting on the cover goes to the side of the block fitting. The pulses move that clear plastic cover in and out pumping fuel into and out of the chamber you can see with fuel in it in your picture and those little clear discs are check valves that let the fuel in from the tank then stop it from flowing out back to the tank.

 

[Sportster-2001-951C-Stock]

Wait a second here, is that a fuel pump diaphragm someone installed on the PTO carb? If yes, that would prevent fuel from entering the metering needle valve I think.......

Never mind, I see that's the mag carb, the fuel pump diaphragm. Without that, the fuel pump wouldn't work very well.

So I see you have the fuel pump apart, from there the fuel goes to both carbs.

 

[powerslave]

on the carb on my pic there is no pump diaphragm. Hell, I'm so busy with other stuff, I'd pay someone to rebuild these right for me...

Wait a second here, is that a fuel pump diaphragm someone installed on the PTO carb? If yes, that would prevent fuel from entering the metering needle valve I think.......

 

[racerxxx]

Hers a set of carbs that I think have possibly never been apart.



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[racerxxx]

I'll assume you have the thin floppy black gasket on the other side? Then the fitted seal.



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[powerslave]

Yes it does

 

[Sportster-2001-951C-Stock]

So far, so good...... This device shown in the photo pumps fuel from the fuel tank to both carbs.

The thin mylar diaphragm moves back and forth by the +/- pressure pulses on the dry side from a hose connected to the crankcase to provide the pulsations. Then, on the wet side this action pulls fuel in through one check valve and pushes that fuel out the other check valve.

 

[powerslave]

Im stumped. I think my new check valves arent seated properly now though.

 

[racerxxx]

I know this sounds juvenile, but did you verify the transfer port that sends the fuel to the other carb is not restricted? Was there fuel in the transfer line? Did you blow through the transfer fuel line? Did you verify on the PTO carb that all you have is the formed seal in there, not other floppy gaskets, correct?

 

[powerslave]

Yes on both.

 

[racerxxx]

Was there fuel in the line?

 

[Sportster-2001-951C-Stock]

So then in other words, fuel is being pumped to the PTO carb and that fuel can enter the metering needle valve of PTO carb, right?

Then it seems the fuel does not pass through that needle/seat of the PTO carb (for whatever reason)?

 

[Sportster-2001-951C-Stock]

I'm reading the other thread, it seems both carbs have fuel in the metering chamber. It appears the PTO carb isn't fueling though.

If fuel is available in the metering chamber then that fuel would follow the path of going through the low speed jet, past the transition ports on it's way to the idle port where vacuum pulls it through these tiny passages. Then once the throttle is opened some small amount fuel begins to flow from the "bypass ports" AKA transition ports, this provides fuel off idle until the large venturi begins to flow, thus are called "transition ports"

Aside: a confusing name for "transition ports" is "bypass ports", but this choice was made during Japanese -> English translation by an office flower.....