after replacing fuel, fuel lines, filter, selector switch and cleaning carbs this '97 GTX runs awesome (50 plus MPH)...for about 30 minutes. then, it loses power and won't rev above about 3500 RPMs. let it sit for awhile and it takes off at full power again, but eventually sputters to a near halt. ski only has 14 hours and set-up for many years before being refurbished, as described above ($1500 in repairs). not sure how to proceed...this is my first jetski