I think this has been asked before but I have a 2011 or 2012 terxy that I bought new three years ago. It has been running fine until this month. It only has about 1000 miles on it. Runs great at idle and all speeds until warmed up (at about 10 minutes) and then won't go faster than about 20 mph and backfires loudly if you try to make it go faster. Still idles smoothly and runs smooth until you try to make it go faster than 20. It is as if there is a governor on it or maybe a transfer of the electronic choke?? to a choke off mode??? I am just guessing here. My problem is it is in the jungles of southern Mexico and the dealer I bought it from doesn't have a clue. If it is beyond a spark plug these guys are idiots. Their answer to every engine problem is a new plug so they already put in new spark plugs.

 

It only happens when it's warmed up?
Is it fuel injected or a carburetor?

 

happened to my buddy's 16 Teryx...dirty air filter

 

Make sure the spark plug is also sparking. Could be an ignition coil going out once the unit is warmed up.