The pump shoe seal is a critical component of the water pump on a Yamaha GP1200R, XLT1200, XLT800 and some other models of waverunner. The cavities in the pump shoe can have entrapped air which can cause cavitation which will severely limit thrust from the pump, causing a lack of acceleration and a slipping clutch type feeling.
This slipping clutch feeling is evident from a rapid rise in engine RPM with little to no acceleration, that sudden rise in RPM can damage the impeller through cavitation eating away at the metal, as well as overrevving the engine.
A simple and relatively inexpensive way to solve this issue is with a pump shoe seal kit, There are several brands available, Riva is a popular choice that I have personally used many times and had great success.
You can watch the video below for instructions on how to install this kit on your waverunner, and purchase a kit from these links: