1100GS poor fuel economy

[ericmcn]

Guys

My brother has a BMW 1100GS, and says its drinking petrol..

he told me put a message here to help him out as to what could be wrong.

On a recent trip he used up twice as much fuel as his mate who filled at the same time and drove the same distance who also had a BMW,albeit a new model.

Any tips?

cheers.

 

[D6]

exaust, ? pot settings?balance, ?the 1200 is a lot better economy wise anyway, just crapper

 

[Colban]

Dirty air filter,TPS voltage OK ?.CO2 level high (can be adjusted with a pot).
What year,miles,has it just started doing it or gradually got worse.