how can i fix my 2001 yamaha waverunner?

my waverunner (2001 yamaha 850 xlt) will not start. will turn over only for a very short time (1/2 or so revolutions) and then stops. almost like it has a weak battery or something is binding up. will turn over find with the spark plugs pulled and no compression on engine, however with the plugs pulled it wants to keep turning over forever and i have to disconnect battery lead to stop it from staying in the starting mode.. battery and starter motor have been replaced and still have same proplem.