1993 Mercury, 9.9, tiller, 2 stroke compression.

[jamz66]

Looking to purchase a 1993 Mercury, 9.9, 2 stroke outboard. Has very low hours over last 15 years and has not been used in about 6 years. Looks super clean-almost brand new. When I first went to look it would not start and run, apparently due to choke issue. Checked compression cold and they were 90psi and 92 psi. Have read many different opinions on what compression should be on a tiller, 2 stroke. Will compression increase when engine is warmed up? Should compression be 100-110 psi cold or warm, or is 90 OK? Motor apparently runs great now, getting ready to go look again.

Thanks!

 

[Bosunsmate]

Re: 1993 Mercury, 9.9, tiller, 2 stroke compression.

Thats fine as they are close together, if they were quite different like 8psi or more apart then it would be saying something worth thinking more about.
As the engine heats up you will get better compression as everything expands and gets tighter and more oil has got on the cylinder wall to fill the gaps between the walls and rings.
The best test is if it does what you want a 9.9 to do for you on the water.
If you do store an outboard for a long period its a help if you run it in a barrel every month or so to keep the seals from shrivelling up.

 

[oldman570]

Re: 1993 Mercury, 9.9, tiller, 2 stroke compression.

A good compression test for the motor is done with the throtal in the WOT position as the cyclenders will get more air to compress and make the readings higher in most cases. The reading you have are fine, if the test was not done as stated, and should run for some time as that motor has been made for sometime and has a good following. Maintance is the key factor to long life of a motor. JMO
Oldman570

 

[jamz66]

Re: 1993 Mercury, 9.9, tiller, 2 stroke compression.

Thanks for the info! Just purchased tonight. Will be getting service manual soon and can't wait to get on the water.