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Fuel Mystery: My Carburetor Is Defying Gravity - SOLVED!

Dr. Frankenstein
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Fuel Mystery: My Carburetor Is Defying Gravity - SOLVED!

Post by Dr. Frankenstein » Tue Aug 27, 2019 3:58 pm

OK, here's a weird one, that I hope has a simple explanation - I have my CA77 all dialed in and ready to go - I have spark; I have compression; I have FUEL - except the fuel won't flow from the auxiliary tank into the carburetor! I open the spigot, and it just Sits there! it won't flow.

Take Off the auxiliary tank, open the spigot, it flows.

I just went through the PW22 carburetor to make sure everything is allowing air/fuel flow, and it does...put it back on the bike and Nada; Nothing; El Zippo...I take the fuel line Off the carburetor inlet, and it flows - put it back on, nothing.

When I went through the carbs I made sure the floats were at 26.5mm and moving/closing freely; I squirted carb cleaner through the needle and seat to make sure it was flowing through there, that was no problem...the pilot jet is clear and unobstructed...

*I suspect the 10mm inlet itself, but that is clear and clean - the only thing I can think of is that the 10mm fuel inlet is too long, and when I screw it in the threads somehow blocks the inlet to the carb itself - if there's no escape route for the air in the tube to go as its being pushed by the flowing fuel from the tank, it would possibly just prevent it from flowing...but I have no idea, so I thought I would put this on the forum - anybody else have this problem?
Last edited by Dr. Frankenstein on Thu Aug 29, 2019 12:42 pm, edited 1 time in total.

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Seadog
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Post by Seadog » Tue Aug 27, 2019 5:34 pm

Strange. Is there a vent in your auxiliary tank?

Dr. Frankenstein
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Post by Dr. Frankenstein » Tue Aug 27, 2019 8:08 pm

A 'vent'? Well, my 'auxiliary tank' is an upside down Polar plastic water bottle with a fuel tap adapted to fit the neck, with a hole drilled in the bottom (or top, in this case) in which I place a small plastic funnel, and is hung with some wire I attached/hooked to the sides...I usually hang it off the right handlebar, which gives me a straight shot to the fuel inlet. I have used this device many times to check fuel levels, but for some reason its not flowing.

I put about a cup of fuel in the bottle, open the cheap little petcock I have attached to the neck, and it has never failed to send fuel where it needs to go, except in this case. Yes, its weird.

Pop the line from the bottle off the carb fuel inlet, and it flows no problem. Put it back on, nothing. The fuel stays right there in the bottle. Tonight I checked the 10mm fuel inlet screw, and it does not appear to be blocking any of the holes in the inlet to the needle and seat...I have no idea why the fuel is not flowing into the carb. It won't even go down the tube from the bottle, even with the petcock switch on. Its very strange. Take the line off the fuel inlet, with the petcock still in the On position, and it flows fine.

Maybe the floats are hanging up on the side of the carb, closing the inlet? When I was in there they appeared to have enough clearance...and even so, wouldn't the fuel still flow down the tube to the inlet?? Its not even doing that...

rrietman
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Post by rrietman » Tue Aug 27, 2019 11:39 pm

sometimes, if your fuel lines have too much dip below carb level, fuel won't easily run to the carb. I have had this occur with stock connections as well as auxillary tank set up. eliminate as much dip below the carbs as possible. open the bowl drain screws to get fuel flowing helps as well. not sure what physics are at work here, probably just air bubbles. more fuel in the tank can make a difference to get things running.
Good luck
Randy

Dr. Frankenstein
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Post by Dr. Frankenstein » Wed Aug 28, 2019 3:58 am

That's the thing, it does not dip below the level of the carb at all; I'd say the line is connected at about a 45-degree angle to the inlet, with a little slack, of course. But it does not dip below the carb. I will try opening the carb drain to see if that helps to get things started. I'll try adding more fuel too and see if that helps. Still, a cup is about 8 ounces...I have never seen anything like it.

AlanW
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Post by AlanW » Wed Aug 28, 2019 3:22 pm

Try unclipping the bowl, let the float hang down, put a small tray under the carb and turn the fuel on. It should flow and if it does then lift the float to make sure it cuts the fuel off. If no fuel comes out work back from there.
I hope this helps, Al.

Dr. Frankenstein
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Post by Dr. Frankenstein » Wed Aug 28, 2019 3:30 pm

Work back from there to Where?? There's only one way into the carb...what do you think it might/could be?

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