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Old 14 May 2012, 17:01   #1
Country: Greece
Length: 7m +
Join Date: May 2008
Posts: 16
tachometer issues

honda 225 and my tachometer got crazy.. always showing more revs than the actuall revs of the engine ...
any ideas if is something to fix or just neeed a new one?

cuteshark is offline   Reply With Quote
Old 15 May 2012, 02:59   #2
Country: UK - Scotland
Boat name: Wildheart
Make: Humber/Delta Seasafe
Length: 5m +
Engine: Merc 60 Clamshell
MMSI: 235068449
Join Date: Apr 2007
Posts: 4,614
If you had said you had just fitted a new one I would have guessed that the pole switch was in the wrong place. I;ve not heard of the switch randomly changing, but you may have a fluky vibration that has moved it.

The tacho counts alternator pulses. if you have more poles in your alternator than the tacho thinks, it will for example see 4 pulses per rev instead of 2. If your switch is set to "4" it will be expecting 4 pulses per rev. If you have a 6 pole alternator it will in reality see 6 pulses per rev. so the tacho will think the engine is going 50% faster than it really is. The only way the tacho knows how many pulses it should see is by that switch on the back.

Did it just randomly start doing this, or have you been mucking about?
9D280 is offline   Reply With Quote

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