gas tank issue

[geol]

I get between 38-40mpg normally with my 1980 GS1000G, Riding yesterday at 105 miles on what had been a full tank, the bike ran out of gas. I popped it to reserve and rode another 10 miles or so into town. Gas gauge showed OVER 1/4 tank when I ran out and the gas gauge is fairly accurate. Stopped at filling station and filled the tank and it took 3.1 gallons and I had ridden about 120 miles total. Why would I run out of gas? Tank is fairly clean and I have had the petcock out in the past and the pickups were clean. I spent a lot of time adjusting the float so the gauge is accurate. I have ridden almost 200 miles on a tank in the past without running out. Yesterday kind of stumps me. Bike is running great otherwise and is a good state of tune. Any ideas?

 

[KEITH KRAUSE]

I assume your tank holds 5 gallons or very close to it? I also assume you typically hit reserve with approximately 1 gallon remaining on a level road?
You rode 10 miles after going on reserve. If you actually used only 3.1 gallons total then that suggests the tank went on reserve after burning about 2.9 gallons which we now know didn't really happen. Your gas consumption was normal.
If you're positive what you experienced was fuel starvation and turning the petcock to reserve immediately fixed the issue, then the first thought would be the main fuel tower screening became clogged or possibly a piece of rubber from inside the petcock or debris clogged or semi-clogged the main fuel passage, the latter more likely.
I'd inspect the petcock's main passage for proper flow by connecting a test line and comparing main and reserve flow. If any doubt, disassemble the petcock and check it completely.

 

[Steve]

... I have had the petcock out in the past and the pickups were clean. ...

Did you pull the petcock to check the screen TODAY? :-k

There is a LOT of stuff that checked out "OK" some time in the past, but has mysteriously gotten worse with time.

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