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I have a Hustler Super z with a 27 HP Kohler Command Twin CV750 engine. It has recently started to lose RPM's intermittently. Doesn't matter if under load or not. I have replace plugs, carb, fuel pump, in-line filter, in tank screens and fuel lines. It always starts, and will initially run fine, sometimes for hours, then it will just drop RPMs. Shutting off PTO has no effect, lowering throttle has no effect. Just before the RPM's come back there is a low pop noise seemingly coming from muffler. Sometimes the RPM drop happens quickly, other times after hours of mowing. When RPMs come back it may run fine for hours or days, or go out again in minutes. Any ideas?

A build up of floating debris in the fuel tank that gets sucked into the outlet hole plugging it then mower runs too lean.

Thanks for your input. I have drained and cleaned the tanks but it made no difference.

Thinking maybe a bad ignition coil, or a valve sticking. Putting on in-line spark detectors to see what happens the next time RPM's drop.

I have a CubCadet Tank w/ Command 27 with the same issue. Completely random drop in RPM, mostly upon initial start. Occasionally, it will drop RPM then backfire a bit and RPM returns. Other times I just shut it down for 10 minutes, then return to no problems.

I've replaced fuel and air filters, checked plugs and fluids with no change. I'll ry to clean out one fuel tank and shut the valve on the other to identify a fuel supply issue.

Bill

Loosing spark on one cylinder due to a goofy ignition module.

That's the first place my thinking went, Ignition coils. The coil packs on Kohlers go out alot. Matter of fact a friend of mine replaces at least 1 a year. He only mows a few acres a week.

I'd be looking in that direction before i cracked the seals on the valve covers.