Measuring RPM

[Poloperson57]

Hi,

I'm in the process of setting up my newly rebuilt mercarb carburettor on my 4.3l mercruiser, and I have just bought a Tachometer to accurately measure the RPM. It's one of those that you simply wrap the wire round the spark plug lead and it picks up the signal and converts it to RPM on the display. So far so good.

However, I need to set the tacho to monitor for 1 spark per revolution of the engine, or 1 spark for every OTHER revolution of the engine. I know 4 stroke engines ignite every other revolution but some still deliver a spark every revolution, even though its not used on the exhaust stroke.

I was wondering if anyone knew how the mercruiser worked? A spark every revolution, or every other revolution?

 

[tpenfield]

:welcome:

You can go with the every OTHER setting . . . i.e. 4 stroke. BTW - which RPM monitor did you get? I have one on my modified snow blower. It is a Searon HM038M

 

[Poloperson57]

Thanks Ted! That's what I'll go with then.

I bought a cheap and cheerful device which is unbranded. The electronics are pretty standard in these things, so it should be as accurate as I need.

 

[Scott Danforth]

For future knowledge

If you have a dizzy, 1 spark every 2 revolutions

If you have coil packs with 2 cylinders per coil, 1 spark per revolution (wasted spark setup)