[mikesull415]

Not sure if this is the best place for this question, but I just got my boat re prop'd and ready for summer. It's a 93 MX19 with the 4.3 merc and alpha 1. Last year she was great, but the prop was pretty rough and there was a lot of vibration at lower rpms. Anyway, it had a 19p three blade aluminum on it and WOT was 4800 - 5000. Put a 19p stainless three blade on it, and now according to the tach it's hitting upwards of 5800. So we changed it out with a 21p but it's still hitting 5200 to 5300. Honestly I think my tachometer is reading off, so that's my main question....how can I go about getting an accurate reading on the RPM's to test it against?

[mikeyt]

It does sound like your tach is reading "off" as that 19" 3 blade should have had you right around the 4800rpm mark at WOT> Here's something to try. Access the back of the tachometer. There is a small dial marked 4 - 6 - 8 which corresponds to the number of cylinders in your engine. Give the dial a spin a few times then re-set it on 6 cyl. Sometimes the tach's brain goes a little funky and the dial spinning cleans it up.

[mikesull415]

Definitely will. Meant to mention I checked that and it was set to the 6cyl option, but I didn't spin it a few times.