I have a 2000 Kawasaki ultra 150 jetski but i cant get it to go over 4,000 RPM in the water.?

Question

2000 KAWASAKI ULTRA 150 REVS UP TO 8,000 RPM ON THE TRAILOR BUT NO MORE THAN 4,000 IN THE WATER. COMPRESSIONS GOOD. I HAVE REPLACED CARBS, FUEL FILTER, SPARK PLUGS AND STILL RUNS EXACTLY THE SAME. PLEASE HELP.

Answer 1

Try using 93 octane gas or use octane boosting additives on lower octane gas.