You can try higher octane gas, unless you're using that already. The combustion chamber design is not the best on these models, so what you can do is limited. The best solution is to machine the head for dual spark plugs which is real expensive. If you don't want to spend that kind of money, there's either using a octane booster, or you can richen the fuel mixture/retard the timing. The timing is relatively simple, just solder or weld up the advance unit stops to reduce the amount of total advance. This takes some experimenting, not all motors require the same amount. I usually start with about 1/8 inch of built up, then ride it to see how it performs. Too much will slow down the acceleration. What you're after is a compromise, some light pinging under heavy load when hot. If you damp out all the pinging, your motor will be real slow. You can also downshift to raise the rpm when it pings, unless it's pinging in 1st gear. If you elect to richen the fuel mixture, your fuel mileage will go down. Some things to try would be a slightly richer pilot jet and raising the needle with shims. Increasing the main jet rarely helps, unless it's pinging at real high speed. Another thing that makes these things ping badly is heavy carbon buildup in the combustion chamber. A good top end overhaul does wonders for the performance, but again, big money. One final note: none of these modifications are approved by Kawasaki or the EPA, so proceed at your own risk.