Tach not reading correctly

Well, here it is Ken ... proof that you were right, once again

While checking things out and re-timing the engine this morning I snapped a few pics of the RPM differences at a few different ranges. As you can see, at idle it reads nearly perfect. As the rpm climbs though it starts to fall off and read a bit slower that actual. Couldn't really tell in the driveway if it continues this curve because I didn't want to push the engine that hard with no load.







And to be sure that digital was reading correctly, my EZtach confirmed the same. Crappy picture because the lead wasn't long enough to get very close to the boat tach, but you can sort of make out that it reads just above 2100



EDIT:   Found a PDF from the manufacturer site on tach calibration tonight so It should be an easy fix. Probably could have (should have) done this today while I had it on the hose but time just wasn't on my side. My anniversary is tomorrow and I have a meeting that's impossible to get out of so we planned to celebrate today. Got a bit of a cold shoulder and the dreaded 'evil eye' as it was when I told her I was spending the morning working on the boat. So alas, this is a project for another day

I have had two boats with Tach issues. Both would read wacky numbers the first or second time out each year. After that they would read correctly. Both would read lower than correct RPM for a while and then suddenly operate correctly the rest of the year.
Little bit of rust maybe somewhere? Don't Know the cause but I had this issue in my Malibu for 20 years and again in my Nautique.

You were never in SLOW mode. That's a different animal

That would have limited you to around 2500 rpm's.

They didn't really have a name, just said that with bad sensor input, a default value was used and idle was jacked up to 800 rpm by the computer.

Thanks Ken - didn't realize there was a change. I'll look in to it, but I have both so should be covered.