2012 nytro - Low power, low top speed, sounds terrible, stalled a couple times

[Matthew457]

My 2012 nytro has been running terrible. Sounds like a lawnmower, has probably half the power is normally does, can only hit about 115 km/h max speed and it’s stalled a couple of times today.
So last year I had all these same problems but after putting fresh gas in it and running 30-40 km, it randomly kicked in and returned back to full power while riding, This was the only ride I did last season.
Now this year it’s doing the same thing. I rode 60 km a few weeks ago but I had a full tank of last years fuel so I was running that. I assume year old fuel was the cause, but I emptied the tank and I’ve done 80 kms today and it’s still running like garbage even with a full tank of fresh fuel and a can of seafoam fuel additive.
I’m assuming something in the fuel system is gummed up from the sled barely being used the last 3 seasons.
Any ideas?
Spark plugs maybe?
Fuel injectors?
Muffler clogged?
I’m not getting any codes on the display.
Thanks!

 

[MrSled]

How many miles?

 

[Matthew457]

How many miles?

Almost 10000

 

[MrSled]

Almost 10000

Sounds like it needs a valve adjustment.