Performance With An Attitude
Kawasaki 750SX Hop-up
By: Ken Faught, Photography By: Donnie Bales

The goal was very straight forward.

Take a Kawasaki 750SX ,and turn it into a 50-plus MPH machine that's inexpensive, operates on pump fuel, starts and idles as well as stock, yet outperforms nearly every craft on the water. It may sound somewhat simple, but in actuality itís not. However, we decided to accept the challenge.

The tough part is keeping the parts inexpensive and able to endure constant abuse. While engine builders have been cranking out freeway speeds for a decade, the outcome often resulted in waterborn hand grenades, especially with the JS550. Pull the trigger and a short while later they'll blow up.

The larger displacement of the 750SX would make achieving our goal far easier, but we were still searching for nearly eight MPH, and didn't want to sacrifice any reliability. That meant shying away from things like dual carbs, total-loss ignitions and other fancy techno-gadgetry.

But Who?

The seriousness of our quest eliminated a lot of companies in the aftermarket front. Originally, we scribbled down the names of over a dozen hop-up shops, but when we added up the projected parts, our wallet cried for relief. One company that seemed to stand out among the crowd was R&D Racing and ace tuner/co-owner Bill Chapin. Over his engine and hull-building career, Chapin has helped mold champions such as Jeff Jacobs, and also Christy Carlson and Victor Sheldon, for whom he has built National Tour-winning 750SX race craft.

So we loaded up our van and headed toward the famed watercraft town of Lake Havasu, Arizona, to Chapinís home. We met at 5:00 a.m. at the racers' hangout known as Body Beach. The water at sunrise would be near ideal for radar testing the small collection of aftermarket parts R&D Racing suggested to achieve our goals for the 750SX.

About The Craft

The Kawasaki 750SX that we were using was a 1992 model with about 50 hours on the engine. This was to be a "real world" test. There were no factory-prepared machines, nor any advanced view of the craft for Chapin. Our testing method was to hand Chapin the machine and have him bolt on the R&D parts before our very eyes in an attempt to perform magic that would work on anyoneís craft. That way, if there were any problems, we could see them first, allowing us to evaluate them accordingly.

The day before the test we had radared the stock machine, in the same water conditions, at 42.7 MPH. This is slightly less than average for a 750SX, but remember, this one already had a fair amount of riding on it, thus our challenge for R&D was a little more than expected.

Break Out The Wrenches

After viewing the craft for the first tiime and realizing that he did in fact have his work cut out for him, Chapin quickly went to work and installed R&Dís Limited Pro Series exhaust system and manifold. Combined with a Skat-Trak 9/17 degree stainless steel impeller, the craft jumped up to 49.8 MPH with only minor carburetion adjustments. That was an increase of over six MPH in just a few minutes.

The next step was to install the R&D Pro Series ride plate. This brought us just shy of the 50-MPH mark at 49.9 MPH. More importantly it made the machine much more stable at high speed, allowed it to accelerate quicker because it could plane faster, and also made the steering more predictable. These are all critical performance elements and are noticeable in both smooth water and in chop.

The next stage was to rejet the carburetor and install R&Dís reed stuffer. For this project Chapin was able to rejet the carburetors in his box van in a few minutes. Although it didnít improve peak water speed, it did produce an impressive bottom-to-midrange gain. A useable type of power that is necessary for race-oriented machines.

Surpassing our goal water speed was achieved with R&D's Aquavein top-loading scoop grate. Although the benefits come in rough water where the scoop grate is able to provide the pump with a better water supply than the stock grate, benefits were noticeable on smooth water as well. Our machine was radared at 50.2 MPH. Just as noteworthy was the fact that we were only an hour and a half into the project and that included all of the radar testing!

The final modification was the installation of R&D's timing advancer which increased top speed to 50.4 MPH even though the water had become choppy with a significant amount of cross winds. A few weeks later we were able to produce 50.8 MPH at sea level.

The Bottom Line

Without a doubt we had acheived our goal. For under $1,100 we picked up 8.1 MPH and easily left the 50-MPH mark in our wake. And after more than 25 hours on the machine we are very confident in saying that you probably won't find a better all-around package for the Kawasaki 750SX. And remember, this was on pump fuel, on a used machine, and yet it still starts and idles as well as stock.

Parts Package
  • Skat-Trak 9/17 Degree Variable-Pitch Stainless Steel Impeller
  • R&D Pro Series 750SX Exhaust System
  • R&D High Performance Exhaust Manifold
  • R&D 750SX/SXI Pro Series Ride Plate
  • R&D Aquavein Top-Loading Scoop Grate
  • R&D Carburetor Mods
  • R&D High Performance Reed Stuffers
  • R&D Timing Advancer
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