Simply putting 1 liter petrol in it and check the odometer when it ends, did for for 5-10 times every time it end around 37-38 and so on
Well its not a good way 2 check milage bcoz 1 litter is too low to check the "AVERAGE" thing, it will just give u results for that lttr..
Proper way is: If ur bike's fuel is empty, fill it full or get 5,6 Litters..(Or incase u already have some petrol, just as the reserves starts fill more fuel at nearest pump and remember how many lttrs uv put in)
Now u know, 1.5 lttr goes in reserve(if empty tank), leave it... keep running ur bike without adding extra petrol 4 nxt few days and when reserve starts check and remember the milage.
For example u filled Rs 455 petrol i.e. 6.5 lttrs. in an empty tank, if reserve starts after Eg: 250Kms, u will know 250/5Lttrs = 50Km/lttr Avg.