I have a gas Mule 4010 that has 800 hours. 799 of those hours, the machine has run as expected.

In March, I replaced the fuel pump, fuel filter and spark plugs. It ran completely fine with regular use on the weekends.

Just recently, it has begun to lose power going uphills in High. We are in the hill country, and right now I have to put it in Low to get up a hill on the property with just me in it. In the past, it would go up the hill in High fully loaded with 4 people without an issue. You can also feel it lose power at full throttle if there is any resistance while driving (starting to go up a small incline). It starts, idles fine and accelerates normally on flat land. No backfiring or smoke.

What I can find online (though the info is scarce) suggests a possible valve adjustment. I checked the air filter underneath the back seat and noticed it seemed moist, sticky to the touch and there was possibly a small amount of oil on it. I ran the Mule without the air filter and still experienced the loss of power, so the filter wasn't the issue.

Curious, has anyone experienced the same symptoms and performed a valve adjustment that corrected the issue?

It seems like an engine/fuel delivery issue. Is there anything I should be checking on the transmission to rule that out?

Thanks for any input.

Do the RPMs stay high and it just slows down or do the RPMs drop?

If RPMs stay up, it's probably a worn belt.

The RPMs drop. Almost like it's starving for gas or if you were to have the choke fully open and hit the gas after it's warmed up.

It's the fuel filter. Mine did it and I replaced the pump. Started doing it a few months later and I ran some Seafoam through it and it cleared.

Thanks for the advice. I will try swapping out filters or running Seafoam this weekend and hopefully that'll clear it up.

That would certainly be the cheapest and easiest way to start. I've found that Seafoam cures a lot of ills. I put it in my 5 gallon cans when I fill them up.

I agree. I know the new fuel pump was pumping enough gas since I could see it in the filter. I did replace with a cheapy, off-brand $30 pump with a filter instead of paying Kawasaki +$200 for their OEM part. Makes sense that the cheap cloth filter could have dissolved or broken apart and caused a blockage.

That's the same one I bought.

You remember there are two air filters on a mule right? This was usually my problem with same symptoms.

I had similar issue and if I remember it was because coil was bad and not firing all cylinders

I had similar issue with exact machine. I changed the fuel pump and corrected it. I didn't buy the OEM pump either, I bought this....

https://www.highflowfuel.com/i-2831...4010-2009-2019-replaces-49040-0719.html.

I haven't had any issues since.

Found and fixed the issue. Rubber brace that holds the fuel pump was cut and falling off the mount. Pump would fall out of its regular position when driving and that was causing the fuel delivery issue on hills. Rigged it so the pump wouldn't move and ran seafoam for the weekend. Running good as new for now.

I heard from a little birdy who just had his 2017 PRO flashed that Kawasaki has a new ECM flash for fuel injected gas Mules in hot climates.
This was after he had constant issues and multiple trips to shop with fuel injection problems in warmer temperatures.

The tech at Kawasaki shop told him all the initial testing took place up North in much cooler temperatures and that fuel curve doesn't work so well for Texas heat.
They also said it is worse for people that use their Mules for more than 10-15 minutes at a time where the motor has a chance to really warm up.