Tach question?

[Surfer]

Took the boat out yesterday, and got close to 6K rpm out of my 350 ...Then realized the calibration of the tach had slipped, found adjustment on the back and reset at idle. The question is how do you determine the real rpm of the motor, and where does the voltage that fires the tach come from?

[MOP]

Hook a tach & dwell meter up at the coil with long leads so you can lay it on the floor next to you to compare the two at speed. Power is taken from grey wire on negitive side of coil.

[BUIZILLA]

If you have a handheld digital tach, shoot it at a flourescent ceiling light to check for calibration accuracy. If it's accurate, it should read 7200 rpm + or - 2 rpm. If it is not within those tolerances, replace the battery and shoot again. Then calibrate your engine tach at 3000 rpm. Doing it at idle could interpolate as much as a 200-300 inaccuracy at top rpm on the scale in question.

J

[Surfer]

Poodle thanks for the offer, MOP, what do you mean by at speed, idle, midrange?

[Tidbart]

You don't need long leads. Just hook a tach/dwell meter to the leads on the back of the tach in the dash. It will give you good reads and is right next to the gauge you are trying to calibrate. :D

Bob

[Wavewalker]

Surfer,
Just superglue the tach needle at 7K and the speed needle at 85 mph and impress everyone. That's what I learned at NcNab Tech School anyway.

[MOP]

I like the long leads hookup direct to the coil for testing to eliminate the possible wiring problem to the dash tach. Run out with coil hook up and back with the dash hook up, if there is much diviation go over connections and grounds.

[Surfer]

Thanks guy's, hey Wave that 6K really impressed me for a second or two.