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Old 19 September 2012, 15:04   #1
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Measuring engine RPM

I need to measure the RPM of my Tohatsu 9.8 so I can determine which propeller to fit when using it on my 2.85m SIB.
Tests on the water have proved inconclusive and I need to determine the RPM at WOT although Tohatsu have recommended the higher pitch prop on this small boat (9.5 as opposed to the 8.5 fitted as standard)

I can see the "Tinytach" at 65 or so, but as I will only really need it once, I wondered if anybody has tried the one from Hong Kong widely sold on ebay for under 10.

It only needs to work once....

Alternatively can somebody sell me a used Tinytach for a reasonable price, then I can sell it on when I've finished with it?
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Old 19 September 2012, 15:09   #2
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I've got the cheap 10 shanghai special, does the job although I can't vouch for the accuracy.

I do think about putting it in the car to see how accurate it is.
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Old 19 September 2012, 17:17   #3
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tried one and seemed to work OK.
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Old 19 September 2012, 17:19   #4
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Got cheapo version , wired mine into ford ka to check, not to far out from cars tacho prob about 200rpm, but calibration may not be too accurate on all ?
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Old 19 September 2012, 18:20   #5
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Thanks, I'll try the Hong Kong one then.
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Old 20 September 2012, 03:14   #6
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I actually ended up buying the Tinytach as it's available from some online buyers for 40 including postage.
I'll probably install it permanently on the engine, and attach it to the transom with velcro.
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Old 25 September 2012, 06:04   #7
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This arrived already from the USA.

The instructions say to wrap the pickup wire round one of the spark plug leads. The unit asks how many sparks per revolution the engine produces.
The engine is a Tohatsu 9.8 2-stroke. Would that be one spark per revolution? Bearing in mind the unit is connected to only one of the spark plugs.
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Old 25 September 2012, 06:47   #8
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Yes..
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Old 25 September 2012, 12:23   #9
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Thanks
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Old 25 September 2012, 13:24   #10
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I thought the tohatsu had a wasted spark, so dont that mean it will fire twice per revolution?
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