1990 Yamaha 225 EXTD

[20pilot]

I am looking at purchasing a boat with a 1990 Yamaha 225HP EXTD. I was planning on doing a compression test. Motor was rebuilt 6 years ago, owner estimates 300/400 hours. Is this the correct way: Pull all plugs, test each individual cylinder during a cold start with boat in neutral? Someone told me to put it at a fast idle? Also, what would you consider to be normal and low numbers when checking the compression. Thanks

 

[boscoe99]

A compression test should be done with the motor hot. Battery fully charged. Throttle wide open. Kill switch activated to prevent sparking. All plugs removed. Install the compression gauge and crank the motor until the pressure stops rising.

Consistency amongst cylinders is important as is the absolute pressure. Ideally the cylinders should be within 10/15% of each other. Minimum specs for that motor is about 80 psi. I would expect that you will see over 100 psi. More importantly, does the motor start well, idle well and run well?

 

[20pilot]

Thanks for the response. I will definetely do that procedure. The boat sounds and runs great. Owner took me for a seatrial and ran for 30 min flawlessly. He told me recently ran 60 miles without hesitation. The boat is a 1979 21' mako with the 1990 Yamaha 225. Boat cosmetically is in great shape, has t-top, stereo, vhf, older garmin gps that does work. Includes a tandem axle trailer, owner wants 5k? What do you think?

 

[99yam40]

That 71 is a very old boat, make sure transom, stringers, and deck is all free of rot and water .
A 90 motor is 24 years old already,
but you are the one to make this decision not us