woow that is a lot... first chek on your gaspipes.. if blak smoke come out is too reach on gas.. then chek sparkplugs.. if they are blak you have to ajust the pilet mixture screw turn it in half turn,, ,, yes if the filter is old would eat more gas but not that much... dhen check yur oil level... sometime the pinflow can stay open and raising your oil level.. but again i do not think that is the issue here.. you are running too reach on gas.. you have to cleen carbs probably because the ethanol in the gas there are lot of bad stuff cloging your carb.. start with pilet screw adjustment first and see how it does