My k bike has 134,000 miles on it and the gas mileage has really dropped in recent years to a miserable 35 mpg/180 miles per tank. I used to get 50 + mpg/240 miles per tank when I first bought the bike with 70,000 miles on it. A recent inspection showed oil fouling on one of the spark plugs some I'm thinking it might need new piston rings ? If you add ongoing starter sprag clutch problems ( bike runs 2,500 miles before I need to do a Motormedic flush- I feel it needs a proper tear-down to clean things properly. I've been advised that will run around $600 for labour plus any parts that might be needed.) then I'm wondering if it would be more advisable to install a used engine ? I've found one for $450 + $250 shipping that has 55K miles on it- I'd still have to install it but it should solve both problems. It seems a better option from a financial point of view - anyone have any thoughts on this ? I understand the effects of wear and tear but have heard of K's with several hundreds of thousands of miles on them and wondered what was considered normal ?