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Not sure how common it is in other models but when I was playing around with different pulleys on my finish mower I discovered the tach acuracy on my 4310 was way off.

I purchased a inductive tach to check and verify engine and PTO speeds. I am still running my machine at or near the PTO mark on the tach but it is actually much slower than 540 at that line.

To get my PTO to 540 my tractor tach was reading over 3000 RPMs. Reading engine speed at the flywheel and comparing to PTO, 2650 at the flywheel produced a reading of 554 RPMs at the PTO with the inductive tach.

At a tach reading of 3000 RPMs my actual engine speed was 2460. Belt tension is correct with a new belt and the mechanical temperature gauge I installed reads right at the thermostat rating of 160F so the alternator SHOULD be spinning at the correct speed.

The bottom line is when I am indicating 2700 RPMs on the factory tach my ACTUAL PTO speed is 463 RPMs.
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