Outboards typically derive a tach signal from the charging system, not the ignition system. Over the years outboard charging systems provided 6 pulses per engine rev. It therefore made no difference whether the engine had one cylinder or a dozen. The only thing that needed to be set on the tach was the number of pulses per rev.. Tachometers for cars typically have a 4-6-8 cylinder selector switch on them because those tachs were looking at ignition system pulses. Since a car engine is a four stroke design, there is one pulse every other engine revolution per cylinder. Therefore a four cylinder provides two pulses per engine rev, 6 cylinders provide 3 and eight cylinders provide 4. So the answer to the question has two parts. 1) yes -- the tach may register. 2) Some math will be necessary to determine a correct reading because you need to determine a) how many pulses from the charging system on your engine (probably 6/rev) b) what the # of cylinders setting is on the tach (use "6") and d) divide the indicated reading by 2 to obtain the correct rpm. To review: The engine is producing 6 pulses/rev. The tach is looking four 3 since you have it set for 6 cylinders. Therefore the tach is seeing twice as many pulses as it needs so you divide by 2.
