CONTINUOUSWAVE

My first measurement of the cylinder pressure of my 1996 Yamaha 50-HP came out at 115, 115, and 100-PSI. Should I be worried?

I didn't test [with the engine throttle set to maximum]--which I later read I should do--but can't imagine it will change the result.

The only way to test your theory that the setting of the throttle position will have no effect on the cylinder pressure you measure is to re-do all the measurements and vary the throttle position.

The pressure measured during a cylinder pressure test cannot be absolutely compared to a standard. We don't the accuracy of your pressure gauge. We don't know the exact conditions that existed during the measurement. Variations in temperature, air pressure, and presence of some oil on the cylinder walls could all affect the measurements.

A general rule for evaluation of the cylinder pressure is to compare the readings from each cylinder; there should not be more than about 10-PSI variation among cylinders. In some two-cycle three-cylinder in-line engines, however, there is an intentional variation. I think the middle cylinder is different in some two-stroke-power-cycle designs.

Is your engine a two-stroke-power-cycle engine? Which cylinder had the 100-PSI reading?

It is a two cycle, top two cylinders were 115-PSI and bottom was 100-PSI. The engine sat for a while. I will repeat the test and post result with throttle set to maximum.

Read the REFERENCE article about testing outboard engines at

http://continuouswave.com/whaler/reference/outboardCheck.html

It contains a suggested procedure for performing a compression check.