What jet skis can you buy for £3,000 these days and how do you improve its performance? If you don’t have 15k for a brand new, high performance jet ski and a 2-3k 2-stroke or a 4-5k 4-stroke is more in your personal watercraft price bracket what should you look for and how can you spec it up and maintain reliability. After deciding he wanted a cheap reliable runaround, Marcel Diner opted for a Sea Doo GTX Supercharged jet ski. He picked up a 2003 185hp for just £3,000. Here’s his story…

Before buying the jet ski, I looked for the usual problem signs of heavy corrosion in the engine bay or signs of water ingestion (by leaving the bungs out etc) and checked that the engine was running fine. The worst thing for 4-stroke internal engine damage is corroded intake or exhaust valves, leading to dropping a valve. The supercharger was engaging and the slip was not excessively low. The 2003 4Tec jet ski does not have supercharger washers, but if you go for an RXP/RXT/GTX215 then it advisable to replace the ceramic washers with metal ones.
It started on the button and the hours were not an issue with a 4-stroke at 187 hours as they are known to go well beyond 400 hours without a rebuild. The jet pump impeller wanted sorting out after stones had gone through it.

After having lots of 2-strokes this sounds really beefy, I like it! The Sea Doo jet ski has great acceleration comparing it against a Yamaha GP1200R, which is similar in speed, although when you get some chop the GPR rider was in the air a lot hanging on for dear life while the GTX S/C was easier to handle with the extra weight holding it in the water longer, ultimately gaining extra speed. Some feel that these skis are too heavy to throw around, but not so. It just takes a little getting used to and they create froth and spray just fine. It’s a good stable ski, easily taking two riders with room for a third.

The front storage bucket is huge but just remember to put an anchor in a canvas bag as they frequently break buckets. Fuel economy is akin to a performance car; very low usage on low revs and drinks fuel at high revs. I barely used one bar of the fuel gauge when riding sedately from Lee-on-Solent to the Isle of Wight but when giving it a a good 15 min blast it went through 2-3 bars. As the ski didn’t cost a fortune and has no warranty to void, the next thing to look to do is mod it, without spending too much or losing reliability.

First and most important on any ski is to sort the jet pump. As is the first place to lose power and the best to optimise the power you have, making sure the wear-ring is in reasonable condition and then getting the impeller pitch right to suit your engine power. Bearing in mind that other mods may change the ideal pitch, you need to plan ahead. Another low price and easy mod is an aftermarket air filter for cooler and more air intake (see pic, the Riva filter sock tucks under the engine at the front), the computer will compensate fuel to suit.

An intake grate can help load the jet pump better and hold the ski to the water better, good for mid-revs but can knock a little top speed off. A performance supercharger wheel is simple to fit and will provide a lot more go, around +25hp (210hp on a 185 or 245hp on a 215). This is lower on a 2003 185hp as they have a 17 tooth gear and spin slower than RXPs with a 16 tooth wheel.

Alternatively, the 185 drive gear can be changed to an RXP one and the RXP supercharger (with or without wheel upgrade) with the 16 tooth gear can be used for 215 or 245hp, but the engine needs to come out for this. The other difference with the 2003 is it has cast pistons, whereas the RXP has the stronger forged pistons, although apparently some users have kept the cast pistons and been OK.

The standard RXP supercharger wheels are about 6psi, the Riva ones are up to 9psi with other billet ones at 11psi. More pressure (psi: pounds per square inch) equals more power. The addition of a racing ECU (I don’t recommend these unless racing) will add another 1psi with higher and longer revs but will need up-rated valve springs and has a higher risk of bouncing the valves.

An external intercooler will add more power through lower air charge temperature but beware, the cheap ones can leak water into the engine.
An aftermarket thermostat can lower the water temperature but can be a pain to change.
So far I have sorted the jet pump impeller, have a Riva air intake filter, 2 degree pump wedge, Worx sponsons, standard supercharger, standard intake grate and it does 63mph, with good acceleration.
The pumpwedge and sponsons provide better handling. The next plan is to add a standard RXP intercooler (fits straight in with a few hoses), an RXP fuel regulator and an aftermarket supercharger wheel, this should see about 68mph.
On an RXP/T I would just go with a billet supercharger wheel and an up-rated jet pump impeller giving about 73mph.
Keep the mods simple and reliability will be maintained.

The GTX S/C rides differently to 2-strokes, it sticks to the water more in chop, is not quite as quick in turning but has a lot more pull in the mid range, where most of the riding is done. It is very stable unlike 75% of 2-stroke models that can tip with two riders at low speeds. It is so stable you could fish off the back if you felt like it!
The other benefit is that no seawater goes through the engine to cool it, only the exhaust section, which needs a short flush after use. It also starts up first time, every time. Other than that it is not as flighty as most 2-strokes but still has the fun-factor.

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