I own 11 year old bike and it has ran more than 1.4 lac KM.For past few months,mileage dropped from 57Km/L to 38 KM/L .Can I do any repairs to increase its mileage and performance ?

I think,you want to retain the bike.You need to fit new Piston set,new klutch,drive chain and sprokets set.De carbonize the engine,silencer and polish the ports.You will get better mileage and performance