tachometer setting

Hi Folks,

Need your thoughts - I just bought an ENM tachometer (Northern Tool) so I wouldn't run the risk of overreving my titan 2.5hp engine. This is a thatsdax rear mount chain drive setup 5:1 gearbox, 10tooth sprocket, 48tooth sprocket, 26 inch wheel.
The tach was set to firing once per revolution out of the box. Just tried it and it shows 7800 +- rpm's going my normal cruise speed of 24 mph. My max mph is just at 30mph. Either I need to set the tach to some other setting or I will be buying a new engine rather soon. The other settings are 1)spark plug fires twice per revolution or 2)every other revolution. I guess the other possibility is that the tach is not reliable at all - but I have read good reviews about this instrument. Anyone have/had experience with this tach and 4 stroke engine's? Thanks

Thanks for the info. I was hoping that would be the case. I couldn't find any calculators on the web that might give me the calculated rpm's/mph with this configuration and I didn't want to reset the tach which may have given me the wrong information. I am presuming that on simple 4 strokes the spark plug fires every other revolution on the power stroke. I've reset it and it looks reasonable. I don't think with my gear ratio's i can over rev the engine. Thanks