Tire inflation! Or brakes dragging. Spin the wheels while on centerstand to see how freely they spin.
Grossly underinflated tires (40% LESS pressure) in cars cause consumption to rise up between 0.2 and 1.5 % which is negligible and cannot even be measured without sophisticated equipment.
People often quote under-inflated tires as a cause of higher consumption while in reality there is very little influence. (to my own surprise)
This is one of the most frequent advices you can read in articles or see on TV.
Here is a great scientific study about this topic, based on thousands of cars, SUVs and small trucks in USA:
http://www.google.hr/url?sa=t&rct=j&q=study%20american%20tire%20inflation%20fuel%20consumption&source=web&cd=4&ved=0CDsQFjAD&url=http%3A%2F%2Fwww.trb.org%2Fpublications%2Fsr%2Fsr286.pdf&ei=Lw0oT77sA5HssgamidXKAQ&usg=AFQjCNEubS14OuCpt_naYix5qdorlvd1PQRegarding this topic, I have noticed the same in the past.
With Peugeot Zenith, I have had spikes in consumption + 50 % just like that. It used to consume 3.2 l / 100 km and suddenly it jumped to 5.
My P250S used to need 4.0 l/100 km, now it is 5.0 l/100 km flat. + 25 % overnight.
These are not scoots with underinflated tires, with stuck brakes, with dirty air filter, with old spark plug, problems with carb or anything else.
I did not drive under different conditions, climate or roads.
It happened "just like that" and never reversed back. Otherwise, scoots performed just like they performed before.
Really, I have no explanation for this, and there should be one. My solution was to stop worrying about that.
