Why does my 2013 RTS have poor acceleration?

[Tmeyer14]

Hello, I just joined the forum and need some help. I have a 2013 Spyder RTS SM5 Rotax 998cc engine that will start up just fine. However, when it idles, it will rev back and forth between 1100-1150 rpms then die. I will restart it, and it will stay running. When I put it in Reverse, it struggles when I try to rev the engine, even when I don't release the clutch. On the road, it struggles to accelerate, especially in higher gears, I have to downshift to get power. In some instances when I accelerate it will stall, then suddenly take off. I already replaced the fuel and air filter, and fuel it with 91 octane no ethanol gasoline, with little improvement in the performance. What else could be the cause of this problem? And has anyone else experienced this? Your help is appreciated.

Thank you.