Fuel tank flow question


Information and questions on GL1200 Goldwings (1984-1987)
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harkgold
Posts: 147
Joined: Thu Nov 03, 2011 9:19 pm
Location: Des Moines, Iowa
Motorcycle: 1984 GL1200 Interstate

Fuel tank flow question

Postby harkgold » Tue Nov 29, 2011 5:26 pm



Ok. On my '84 GL1200 Interstate I've removed and cleaned the fuel tank, petcock, and gas cap. All now look like new. And I back flushed through the petcock just in case there is some kind of screening device inside the tank.

After I reassembled all of the components I wanted to test the fuel flow out of the petcock, so I put a clear section of tubing on the petcock and placed the opposite end in a fuel can on the floor. I then put three gallons of fuel in the tank and turned the petcock to its ON position expecting to see fuel just come blasting through the clear tubing and into the can. However, that is not what I experienced. Even after doing all of this, fuel just kind of trickled out of the petcock, down the clear tubing and dribbled into the fuel can.
Needless to say I was quite disappointed to see this.

AND THEN IT HAPPENED!!........I took the end of the clear tubing out of the fuel can.....cleaned it off with a rag.....lifted it to my mouth and gave the tube an ever so slight draw of vacuum on the tubing.....AND SUDDENLY HERE IT CAME!!! Fuel immediately filled the tube....I quickly plunged the free end back into the fuel can and a solid stream inside the tubing began flowing freely and siphon the fuel from the tank.

As the first container approached being full I reached over and turned off the petcock and switch to an empty container. And this time it happened again when I turned the petcock back to its ON position, again I had just another small trickle of fuel until I gave the tubing that ever so slight draw of vacuum to get it started and again it freely rushed out of the tank.

I completed this same cycle three times to empty the three gallons out of the tank and each time it required an ever so slight vacuum to get the flow going strongly again.

And I began to wonder if this is partially the reason the Gold Wing requires an electric fuel pump utilizing it to create that initial slight vacuum to draw the fuel from the tank, through the filter, and then to the carbs.

Is it possibly the design of the tank......the placement of the petcock.....which is higher on the side of the tank.......and the draw tube being lower than the petcock that requires this slight vacuum action to get things flowing?

The tank on my '78 Suzuki GS750 has only a petcock.....no draw tube......and the fuel flows freely with no vacuum draw required. But that fuel system is totally gravity fed with no electric fuel pump.

Any thoughts anyone? Am I on track with my thinking here. Or do I need to continue looking for some kind of additional fuel obstructions?

Thanks,

Harkgold :?:



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Re: Fuel tank flow question

Postby WingAdmin » Tue Nov 29, 2011 5:30 pm

You've got no problems. If you had filled the tank full, the stream would have started on its own, and it would have continued to siphon out the entire tank. However, due to the position of the petcock, it will not gravity feed unless the tank is around 3/4 (or so) full - that's why the fuel pump is required.

Once you started drawing the fuel out (against gravity) with your mouth, then plunged the tube into your gas can, gravity siphoned the rest of the tank empty.

harkgold
Posts: 147
Joined: Thu Nov 03, 2011 9:19 pm
Location: Des Moines, Iowa
Motorcycle: 1984 GL1200 Interstate

Re: Fuel tank flow question

Postby harkgold » Tue Nov 29, 2011 8:14 pm

WingAdmin wrote:You've got no problems. If you had filled the tank full, the stream would have started on its own, and it would have continued to siphon out the entire tank. However, due to the position of the petcock, it will not gravity feed unless the tank is around 3/4 (or so) full - that's why the fuel pump is required.

Once you started drawing the fuel out (against gravity) with your mouth, then plunged the tube into your gas can, gravity siphoned the rest of the tank empty.


Whew.........thanks for the good news!!!!
Harkgold


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