So this has been going on for about 2 years now, and this years first launch seemed the worst yet.
My tach does not give accurate readings, I know this because of the following:
-sound of the engine doesn't match what the rpm says
-sat. the reading at idle was 2k (after a clean carb and link and sync)
-sun. the reading at idle was 1k - same feeling to sound/vibration as sat.
-on sat. WOT was reading past 6k (dial didn't go any further) and my engine, according to mercury, cannot physically exceed 5500rpm and WOT
-WOT throttle sounded like it was at 5500rpm, not sounding like it was at the bleeding edge of failure.
Now, 2 years ago, my mechanic did some quick tests on the electrical on my engine for some other completely unrelated problem because fuel wasn't making it to the engine (end result was a bad primer bulb).
He said that my switchbox assembly was giving inconsistent readings, explaining the tach, and also stated that it's a sign that they could go bad, and it can happen at any time, and when they do go bad, bad things will happen to the engine.
I would like to plan on replacing the switchboxes next season (after my own personal tests) but they are $200 a piece OEM and I need two of them. I would have to go third-party, but definitely not right now.
does this sound reasonable? or - is there other areas i can diagnose to try to get a better reading on my tach; hopefully as a cheaper (if not temporary) solution? Maybe it's just a bad tach? maybe something else?