Fuel capacity discrepancy

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Fuel capacity discrepancy

Slimmers
Hey, I was just wondering about the fuel capacity of my 1981 CB750. Manual says it holds 5.3 US gallons. When my bike started sputtering today, I switched to reserve and continued on my merry way. Manual says reserve is 1.3 US gallons. I made it only 18 miles and ran out of gas. Luckily I was 1/2 mile from a gas station and got a great workout pushing a 500+ pound bike that far. When I filled it up to the top, it only took 3.9 gallons to fill. Anybody know what's going on here?
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Re: Fuel capacity discrepancy

TOOLS1
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Sounds like the filter screen on the petcock might be plugged up around the bottom. Pull the petcock off, and clean it. Another thing if it happens again. Try leaning the bike over to the left. Sometimes the gas will be trapped by the tunnel on one side.
TOOLS
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I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
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1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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Re: Fuel capacity discrepancy

Slimmers
Thank you. I'll check it out
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Re: Fuel capacity discrepancy

sgtslag
If it were my bike, I would throw out the screen, and add an in-line paper filter:  catches finer particles; easily checked, and replaced; cannot corrode.  My '79 had a screen from the factory, but one of the PO's removed it...  When I discovered that I had no filter at all, I put an in-line one on it.  No worries or issues since.

I would also recommend you SeaFoam that tank, and fuel system, if you have not already:  will dissolve varnish deposits, throughout the fuel system.  It will not harm, but it will do plenty of good, for the fuel system.  The prescription is:  1 oz. of SeaFoam per gallon of gasoline; 1 oz. of SeaFoam per quart of oil (in the crankcase -- check oil frequently, change oil and filter as soon as the oil darkens with sludge freed from the engine/transmission!).  Sorry if I'm preaching to the choir, but this stuff is fantastic, in my experiences.  Use it every Fall for winterizing the bikes for the long sleep until Spring:  top off the tank, add 1 oz. of SeaFoam per gallon of gasoline, stabilizes it, prevents varnish formation -- starts, runs perfectly in the Spring, after sitting for 3+ months.  Cheers!
1979 CB750K (sold, 2012, but not forgotten)
1983 Kawasaki 440 LTD Belt Drive (sold, 2011)
1993 Kawasaki Voyager XII
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Re: Fuel capacity discrepancy

LukeM
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+1 to the Sarge.

Once I got the carbs clean enough to get my bike running, I ran three cycles of Seafoam through the gas tank.  It does help keep things clean. I haven't had to use it lately.  I'm not 100% positive, but I think it may discolor the spark plug insulator a bit (turned my plugs a shade of orange).  Might have been crud that worked through the system.  I've read where octane boosters tend to do that.

But I agree: Seafoam is magical stuff. Look for it at auto parts stores.  Typical price is about $10 US for a 16 ounce can.

Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.