How do I check the tach for accuracy ? I quess you can tell by now that I'm a newbie ! & eager to learn.

No problem - the best way to learn is by asking questions!

I've seen analog tachs that were off by 500 rpm! If you have a digital tach tied into the engine computer/Engine Management Module (EMM), it should be fine. You can check an analog tach on an E-Tec by hooking up a laptop to the motor with diagnostic software in it and comparing rpm on laptop to the tach reading. Sounds like you have a carb'd 2-stroke motor however, that may not have an EMM, only an electronic ignition. In that case you'll just have to hook up a known good tach to it. There are handheld optical tachs that use a strobe light on a timing mark that are very accurate. If you're looking at buying a prop from a dealer, maybe they would check it for you.

A tach/dwell meter. Been a long time since I set dwell angle.

Welcome and what year/model is the power?

Most OMC`s run 950 0n mufffs, 850 +/- 50rpm in water, and 650 +/- 50 underway at idle.

If you see those numbers on a carb`d motor, you are fine with the tach reading.

Is that a system check tach from omc?

Cheers,
GFS
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Thanks gfsm, that should be simple enough to check. The motor is a 1997 C115TLRW 4cyl. carbed two stroke & I'm in the process of installing a new Faria tach.