My Yamaha XL 700 has lost a considerable amount of power over the past year and a half. I have no idea why but now it wont even go over 20 mph, but seems to run fine up to that point. Help, Ideas, anything?
Have you switched out the spark plugs and fuel filter? Do that first as that is the cheapest fix and is a very common cause to the problem you are having. If that does not work, check your impeller and shaft for damage. If those are fine, then check your engine compression. Also, drain the fuel and maybe see if water had not gotten into the fuel tank or fuel system somehow. What is your jet ski doing when it only goes 20 mph? Does it make any different sounds, bog out, what?
at 20 mph its just fine. it just feels like 20 is the max speed, no funny noises, no cutting out. we don't use it very often though- maybe 6/7 times a year. is there some sort of buildup that could occur somewhere due to infrequent usage?