I'm not sure, having just bought the car two weeks ago. One of my rear tires has a leak, so lots of that tank was on a severely underinflated tire. I do get a fair bit of smoke on a full throttle acceleration. Valve adjustment or mixture setting?? I never knew this was adjustable. It has 263K miles. The first tank, not driven out by me, might have gotten 26.8 mpg mostly stop and go highway if I can assume the trip odometer was reset at the time it was refueled. Thanks for the advice on the cleaning; probably most of the car would benefit from a painstaking cleaning.