Re: Pulses per Rev
No prob. The "revolutions" are full turns of the crankshaft. With each turn of the crankshaft, each of the pistons goes up and down once in its cylinder. In a two-stroke motor, for every cylinder there is a spark each time the piston goes up; in a four-stroke it's every second time. The cylinders take turns sparking. So either once or twice per crankshaft revolution (depending on two or four stroke) there is a pulse at the coil (initiating a spark) for every cylinder. It's these pulses that the tachometer knows about---so you have to add the info about number of cylinders and two- versus four-stroke to enable it to tell you about rpm's.<br /><br />SO, if you have, say, a four cylinder two stroke, there will be one revolution for every four sparks (pulses). If you have a three cylinder four-stroke, it's a revoltion for each one and a half pulses. If you tell us what the settings on your tach say, and tell us the number of cylinders and two- or four-stroke, we can tell you what setting to use. Most tachs made for auto engines have settings or scales for 4- 6- and 8-cylinder four-stroke engines.<br /><br />In some cases, the tach won't have an exactly appropriate setting, but it makes no difference, because at any setting all you have to do is to multiply or divide the tach's reading by a number. My tach doesn't have a 4-cyl setting, so (for my 4-stroke 4-cyl Mercruiser) I multiply the 8-cyl readout by 2.
