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Idle RPM has changed since I bought it, using info from this site, I have tuned it a little bit, it still is a little high when idling in gear... why would you ask?
Because it may not be set correctly....If it's reading higher than normal at Idle, it's possibly reading higher than it should at wot too.<br />This "may" indicate the tach is improperly set or possibly even "broken"...
One thing that has me confused is the ratio of the 40hp for use with the above chart.<br /><br />The OMC manual lists the ratio as 12:29 (.41).<br /><br />So that means the ratio is actually 0.41:1 or 1:2.41, right?<br /><br />If so, do I use the 1.0 ratio on the chart and divide by 2.41? <br /><br />That would work out to 5000 rpm = 71mph (1.00 ratio) then multiply by 0.9 to get slippage = 63.9. Then divide by 2.41 to get speed based on 2.41 ratio = 26.51 mph. But I do 30mph with no load. So what am I doing wrong with the calculations?
Here's a better version of that chart. At the bottom of it, you can even input your specific numbers for pitch, gear ratio and rpm. link<br /><br />Edit: please feel free to save a copy of that spreadsheet onto your own PC and amend it however you want.
That is the replacement, but you can always have your existing prop repaired, but before you spend money on the prop, I'd say let's make sure the tach is right...we "may" not want a 21P.
