BMW R100 fuel tank air lock

[Gromit58]

First big trip out on my 1980 R100. Thought I would test the fuel capacity/mpg. So it's a 22L tank with 5L reserve.

I estimated 200 miles would be an ok target.

I ran out of fuel on main tank at 180 miles, 1 mile from home. Switched on reserves and nothing but coughing and spluttering but somehow got to the fuel station. Filled up with 17.5L of fuel. So somewhere I'm missing 5L of fuel. Any ideas? Thank you.

[M620]

Just a thought have a look at the fuel filter on the top of the tap - the one inside the tank. On my 79 R65 the very fine mesh needed a clean when I took the tap out. That could restrict or even block the flow on the reserve position.

[Gromit58]

Cheers