mercury 60hp lack of power

[kaytree]

I have a Mercury 60 hp (red/silver band) which is on the back of a Shetland 535. i believe the engine is circa 1990.It starts good, runs good,not very noisy but won't open up like the prevoius engine i had on the boat which was a mercury 60hp brown band and was a lot older. I reckon i am only reaching 60 percent of the power i was achieving with the old engine.<br />I have done a compresion check and thee is 125 PSI in each cylinder. i have checked all the controls and they all seem to be functioning ok.<br />The only thing i can think of is that it has a different propeller, but would this make the power loss so great ??<br />how nay advice greatly appreciated

 

[Parkstribe]

Re: mercury 60hp lack of power

The first way to figure out if the prop is the issue or not is to do the following:<br />1) Determine the Wide Open Throttle (WOT) RPM rating of your new motor ... look in the motor's owners manual or call a local dealer if you don't have the owners manual. A "typical" WOT RPM rating is in the 5000-5500 RPM range. <br />2) With your boat carrying a "normal load" of people and equipment, take your boat onto the water. Open the boat up wide open throttle and trim the boat out to the "normal trim/tilt" setting you typically use. At full speed and trimmed out, look at your tachometer and record what the RPM's are. <br />3) If the RPM's are within the WOT RPM range you previously determined in item #1, then the prop is the correct pitch for the motor/boat combo. However, if your boat is operating at RPM's below the WOT RPM range, then the pitch of the current prop is too high. If the boat is currently running at RPM above the WOT RPM range, then the current prop's pitch is too low. <br />4) If/when you determine you need to change props, a good rule of thumb is that for every 1" change in prop pitch, there is a change in WOT RPM of approx 300 RPM. <br /><br />Your issue may have nothing to do with prop pitch, but the above info will determine that for you for sure.