Yea, that is extremely common. I just gave up on those junk crap exhaust gaskets. It would be cool if someone could engineer a better gasket that would make it to at least 3 or 4 thousand miles
Oh, and Mario Shi, that does sound a bit low to me. I mostly ride in the city and on back roads, with the occasional interstate ride, and I average around 85-95 miles per gallon on my 1986 Elite 150 Deluxe with an 87 engine. I, like you, don't exactly accelerate lightly from lights, and I hold 65 mph at times. It sounds like you might need to adjust your valve timing, replace your air filter, adjust your carburetor, check your transmission, and so on. 62, is a lower MPG for a 250 cc scoot in general. What speed are you topping out at? I top 68-70 mph.