check compression on 1986 70 Yamaha???

betag2 · #1 July 2nd, 2004, 08:49 PM

How do I check the compression on a 1986 70 Yamaha? Do I need to ground the plugs or can I just pull the safety kill switch? Do I test W.O.T.? What should the pressure be?

thanks

rickdb1boat · #2 July 3rd, 2004, 04:52 AM

Get a compression tester(Screw in type) and open the throttle all the way. pull the lanyard and see what readings you get and post back with them... Over 100PSI and real close together would be fine... MAy be a bit lower, do to the age of the motor. The main thing is that the readings are within 10-15% of each other and no more..