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rpm diagnostic tool

J

JP102

New member
1980 40 hp merc (2cylinder 2 cycle).

I have an automotive 4/6/8 dwell and tach diagnostic tool that I want to use to tune the outboard. I have it hooked to one of the posts of the rectifier. On the 6 cyclinder scale the meter shows 800 RPM. If I recall correctly, the conversion is to multiply by 2, so in reality the OB is idling at 1600 RPM, which is too high. Any thoughts on the tach and the conversion multiplier?
 
I do not know. I think the Tach is counting pulses in a length of time and coming up with the right answer: '800 Rpm'
Why did you use six? Wouldnt four have been closer? I'm asking because I dont know.
 
The meter displays all three scales. I picked 6 because it was in the middle and I can't remember if the meter went from 8-6-4 or 4-6-8. Either way the values were 600, 800, and 1200. 6 was in the middle.
 
That 4-6-8 is for cylinders on 4 strokes. You'd need a 12 cylinder (4 cycle) tach setting for an outboard's 6 pole alternator output reading.

Jeff
 
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