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3 cyl 4 stroke rpm question

L

Lund Rebel

New member
F40 hp Yamaha that I'm putting a RPM/Hour meter on it.It's a cheap one that you wrap the wire around the spark plug wire. My question is with the 1 spark plug fire at each complete revolution or the gauge has a setting of 3 sparks for 2 revolutions. The wire can only touch 1 spark plug wire.
Not sue which setting to use. The gauge has several settings to choose from. Any suggestions??? THANKS
 
As your motor is a four stroke, the spark only fires one every two full revolutions. As a result 500 sparks a minute is 1000 RPM. The exception to this is when you have a waste spark ignition system where one coil services two cylinders (something you won't have in a three cylinder motor).

So my understanding is that you wrap a single HT lead and double the count of sparks to get your RPM.

Stuart
 
DangarStu said:
As your motor is a four stroke, the spark only fires one every two full revolutions. As a result 500 sparks a minute is 1000 RPM. The exception to this is when you have a waste spark ignition system where one coil services two cylinders (something you won't have in a three cylinder motor).

So my understanding is that you wrap a single HT lead and double the count of sparks to get your RPM.

Stuart
Click to expand...

THANKS< The meter I have it has several settings , I think there is one for a 3 cyc, 4 stroke. Just not sure about it. Put it on my lawnmower to play with it and has to use some off the wall seting for a single cylinder engine to get a 900 rpm reading. I figure I'll have the correct one when I get 800-900 rpm idle and 5500 approx. max rpm like the owners manual says.
 
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