CONTINUOUSWAVE

Today I had a chance to get out my 1989 Mercury 90-HP. The maximum RPM was 4,000 and boat speed was 25-MPH. It was windy and choppy.

[Later more information is provided. The recommended wide-open-throttle engine speed for this 1989 Mercury 90-HP is said to be 5000 to 5500-RPM, the boat is a Montauk and assumed to be a 17-foot model, and the anticipated boat speed is thought to be 42-MPH--jimh]

[What are your] thoughts?

A 17-pitch propeller.

Thanks.

Check plugs, see if you are firing on all cylinders.

Need more data:

--what is the manufacturer's recommended speed range for this engine at full throttle?

--what is the gear ratio?

--is this limited data you report supposed to be something abnormal?

--what boat is this data about?

Montauk 17
Should be [5000 to] 5500-RPM
42 MPH top speed

Use an inline spark check tool to verify you have spark on all cylinders.

How many cylinders does this engine have?

Is the engine a two-stroke-power-cycle engine?

Does this engine use carburetors?

Has the boat speed previously been 42-MPH at WOT?

What is the gear ratio?