Sounds to me like the tach is set up for a 2-stroke motor.
See if there is a way to configure it for a 4-stroke motor.
If the tach thinks it is reading for a 2-stroke, it will show the same
number of RPM as there are sparks. So if the motor is spinning at 3000
RPM, the motor (since it is a 4 stroke) will be sparking every other
rotation of the crank or 1500 SPM (sparks per minute) = 1/2 motor RPM.
Since the tach thinks the motor is a 2-stroke, it will show 1500 RPM.
hope this helps
-alfie
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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