A 4 stroke engine fires 1 time for every 2 crank revolutions..
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Anyone know how many sparks per revolution on a 5O HP 4stroke Tohatsu?
Trying to set up a tiny tach to check prop.
TIA
Ray
Mark 1:17 ...I will make you fishers of men
A 4 stroke engine fires 1 time for every 2 crank revolutions..
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"G", SCOTTY1094 LIKED above post
Intake stroke and compression stroke make one revolution of the crankshaft, power stroke and exhaust stroke make the second revolution. Your plug fires at the top of the compression stroke. A 4 cylinder 4 stroke would fire 2 times per crankshaft revolution, a 6 cylinder 3 times and so on. I think a 50hp outboard is 3 cylinders correct?
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Last edited by Tex_79; 11-27-2019 at 09:04 PM.
Not always. Many have a waste spark system that fires every revolution, especially multi-cylinder engines which have companion cylinders, where one is at TDC exhaust, while other is at TDC compression, in which case both cylinders can be fired by one dual-plug coil.
Many small magneto engines fire once per revolution as well, the coil is energized every time the flywheel magnets go past it, whether the engine is on the compression stroke or not.
I have no idea if any outboards are set up that way, but I would not be at all surprised if it fires once per revolution, doing it that way is often much simpler.
I think they all use that waste spark now days. So it would be 1 spark each revolution.
Fair Winds and Following Seas
Bill H. PTC USN Ret
Chesapeake, Va
That is very true but I’m pretty sure 3 cylinder outboards don’t use a wasted spark system but I could be wrong.. an easy check would be to see what your tach reads at idle, should be +/- 800 rpms, if it’s reading +/- 1600 and obviously not idling that fast your spark per revolution setting is too low. If it’s reading +/- 400 and obviously not idling that slow your spark per revolution setting is too high.. it will for sure either be 1 spark per 2 revolutions or 1 spark per revolution it’s not going to be higher then that
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Last edited by Tex_79; 11-27-2019 at 09:45 PM.
Clint LIKED above post
Well, no consensus but at least a starting point.
I'll see how it goes.
Mark 1:17 ...I will make you fishers of men
Well it must be 1 spark/revolution. That's the setting I had to use to get correct reading.
Mark 1:17 ...I will make you fishers of men"G", crappiemax LIKED above post
Is your motor a 3 cyl? I want to get a tach for my 25 hp 3 cyl suzuki but cannot find a tiny tach that indicates it can be used for a 3 cyl. Please advise if you get one to work on your motor if it is a 3 cyl. 4 stroke. Thanks
Mine is a 3 cylinder. I had an older one that works but my new boat is a stick steer so I had Tiny Tach make me one with 16' lead wire so it would reach front seat. Got it in less than a week.
The only outboard they say it won't work on is a Honda, no idea why it won't.
My older one was not made by TinyTach.
Lots of different versions on line. I ordered this one directly from Tiny Tach. Good customer service and fast.
Mark 1:17 ...I will make you fishers of men