The Yamaha 6R8 Pump System

These Yamaha jet drives are an inexpensive and simple unit to fix and upgrade. Having decent part availability is one of the main reasons for making ownership of something like this reasonable. This pic of a whole unit I found on the net has a little corrosion on it. I'd always be wary of pump systems that have lived in water, especially salt water.

Many examples of bad performance on these Whalers jets is due to worn impellers and wear rings surrounding the impeller. If there is more than a 0.6 MM tolerance between the impeller blade and the duct, they'll need replacing. Lost suction and cavitation are enemies of jet drives.

Here it what my pump system looked like removed from boat. I left the tunnel in the boat because the seals in all the shafts looked great.

When I looked a little closer I was surprised to see a prior owner had installed a SkatTrak 9/17 stainless impeller.

This is explains why I was happier than others with my perceived "stock" performance. ;)

After tearing out my unit to inspect bearings and impeller I decided to replace the wear ring with a Delrin unit from Impros. Impeller wear and damage can definitely cause loss of power and cavitation, especially when there is gaps between the wear ring and impeller. The revised pump housing with a Delrin liner costs about $150 to your door and can be found various places like SBT and Impros. These allow you to replace the wear ring in about an hour for about $35 down the road.

The staff at impros really know about these impellers and have various options available for new, used (fixing used) or upgrading your entire system. I'm considering upgrading the impeller to a current SkatTrac slimline model next Winter.