Couple clarifications: Is this a '98 XP or an XP Limited? The service manual only shows me XP came out as LIMITED.
Fuel lines are old grey -> "They look great"...yeah from the outside. They NEED to be replaced with standard 1/4" automotive fuel lines and the fuel selector switch too and the fuel filter gasket too.
My strong guess is the carbs need a good service/rebuild.....let's face the facts, the ski is 22 years old.....just "cleaning" a carb at this point doesn't tell us enough or do it any justice.....so, might as well start fresh and do it right. Get genuine Mikuni parts kits, get the Carb rebuild sticky POST (top of the forum and follow it -to the letter) and get the correct carb spring(s) = 95 gram (the carb kits don't necessarily come with the right springs OR you need to know which one is the 95 gram). Low speed screws OUT 2 turns +/- 1/4, High speed screws = 0. Carbs synchronized when put back in and the idle adjusted and synced to the oil delivery - assuming you still have the stock oil pump in service.
EVERYTHING about these older ski's is good battery and good fuel delivery.....without either.....you won't go very fast or get very far.