I just bought a 91 yamaha waverunner 650 and it wont start. Its getting fuel and spark but still isnt working. The person that had it before me said they had it checked by a mobile marine service and they said it needed a piston. How would I check to see if that is it?

cmclean, July 2008

You need to check the compression with a compression tester or take it to someone that knows how to do that. It is simple. screw the tester into the spark plug hole. Make sure both plugs are out of engine. Crank over engine and compression will show on compression guage. It should be over 100 lbs.Check both cyllinders one at a time. If compression is good check your spark. My 1990 650 has a hard time starting when cold. I have to open engine hatch and push down on the choke lever on carb and then start engine. Once it starts it will start good all day long.Both my 650s do the same thing.

Randy, July 2010

I've got the same problem with my 92 waverunner - what should the compression pressure be at cranking speed?

Danny, September 2008

compression test

pat, August 2008