Check the governor. Over time (years and hours of operation), they can slip on the shaft where it is tightened by bolt. Governors rarely need adjustment, but it is possible. In the last month, I had two that needed to be reset. Hook up a tachometer and it should be reading around 3200 rpm on a mower. If it is dropping 500 rpms under load, that is a problem.
If the flywheel key is intact the ignition timing is correct.
Yes I do. This particular model has hydraulic. I believe It's possible to pull the valve covers and rocker arms then use a magnet to retrieve out the lifter. With that giving me a small window to see the lobes on the cam or have a look at the back side of a lifter. Normally I've seen I worn lifter come with a worn cam.
Yes it still has the original DSAI speed advance coils on it but ordering directly from dealer they did away with the original and updated.
Remove lifters from lifter bores. Use a hydraulic lifter tool. Do not use a magnet to remove lifters. Mark lifters by location, as either intake or exhaust, and cylinder 1 or 2. Hydraulic lifters should always be reinstalled in same position. Right out of the Kohler repair manual for this engine.
Did you ever solve this?
Think I may have answered this previously but that is typical of running on one cylinderDid you ever solve this?
I'm experiencing the same problem with a Kohler CV740 on a Gravely 260z. Runs fine with a new carb/filters/fuel pump/spark plugs/etc etc but as soon as I push the sticks forward the motor (rpms) start to slow down. With PTO engaged it's even worse. It winds down to about 20-30% and barely stays running until I disengage the PTO and pull the sticks back to neutral. Compression is good (170-175psi), as is the gas. Sounds very similar to your issue. Hunting for answers here.