Jet Ski 650 Sx for Ocean Riding

I own a stock 89 Kawasaki 650 SX Jet Ski, except for a stainless SOLAS impeller. I usually ride on the rivers and lakes in Virginia. Every now and then, I get to do a little ocean riding at Virginia Beach. Im looking to squeeze a few more hoursepower out of my Jet Ski. Im hoping you can help. I noticed you frequently recommend air filters for better flow. I took a look around and there are many sizes, shapes and designs to choose from. Also will advancing the timing help my performance? And Should I mill my head?
Troy

Troy
The best performance you can do is add a performance exhaust system. It will improve performance all through out the power band. 
For timing your ski is fitted with an adjustable stator plate assembly. The timing can be changed (advanced) simply by rotating the stator plate assembly counter clockwise. Be careful not to advance your ignition timing to much from factory setting . Only 3-4 more degrees are needed to help improve low-speed response. 
  You can safely cut your OEM head to get more compression. I recommend Removing .070 (seventy thousands) from the surface, then open up/machine  the squish band area to your exact bore size. be sure to keep stock chamber angle too. This will give you approximately 170-175 cranking compression. You will still be able to run pump gas 92.
After market flame arrestor filters are all pretty equal. The main point it to improve flow.
J tec