I have a 2010 Mule 4010 with the FD620D Kawasaki fuel injected engine.
Runs good at startup, but slowly loses power to the point where it sounds like it runs rough at higher engine speeds and feels like its misfiring. Idles fine though.
If you shut the key switch on and off it will run great for a few more minutes, and slowly lose power. You dont even need to key it off long enough for the engine to stop, just a quick on/off and it runs great.

So far here is what I have done:
Adjusted valves
New fuel pump/regulator
Tune up-Plugs, filters
Cleaned throttle body
Checked/swapped coil packs with another good running engine

I am starting to lose my mind with this thing, I cant make any sense of it at this point. I thought maybe fuel injectors were going out, however it doesnt make sense that a key on/off would effect that?

Ant ideas?

 

We have 7 of these and they all have the same problem was wondering if anyone has been able to fix them

 

I have its brother lol, it was brought to me it wouldn't idle, cleaned throt body, cleaned tank, replaced filter, new plugs. Starts and idles now, driving it, it starts to lose power, shift to neutral it's runs and idles, put in gear it runs good, might go a short distance or may go a few miles before it does it again, I'm at a loss, any ldeas?

 

I have a late model Mule that is giving me problems. I saw a similar issue on this forum but will now answers/solution.

My Mule will start and run for a while and then loses power - the engine is still running...a little rough but running...but I lose speed and can't even make it up a small hill without dropping into low gear. It seems to get worse with time - can shut off and leave for a while and restart and it will run for a while but eventually (sometimes a few minutes, sometime up to 30 mins) it will lose power.

Any ideas?

I am running at a little bit of elevation (4000ft) but that wasn't an issue for the first 5-6 years I had the Mule.