2003 gtx di rotax, lost top end speed + wont start in the water

[dave1]

my 2003 gtx di rotax engine lost 10 mph off the top end, i removed the rave valves cleaned them re placed them, when the ski is out of the water it starts ok, when you rev it full it miss fires but does not bog down and white smoke blows from the rear, when i put it in the water it started first time but has no power and then cuts out and will not re start untill you lift it out again,

any help would be great thanks

 

[ski-d00]

check compression? change plugs?

 

[Bills86e]

Check the fuel pressure at schreader valve. read yo manual. Gas goes bad in about three weeks, so use Stabilizer as it helps DI system also.