I have 20 hp GD longtail with a BS Vanguard on it. The motor runsgreat and starts well. But the RPMS surge. Without touching the throttle the rpms will move up and down about 200 RPMS. I can't figure it out.

sounds like a fuel issue.

I would guess your automatic throttle / choke spring is getting weak. or your air to fuel mixture is off. but start with fresh gas and see if that fixes it.

i think i seen your 20 hp on youtube. there is one on there that is runnin in the mud and sounds the same as what your decribing. go check it out and see if its the same thing. it might be just the way your motor runs. did it do that from factory or did it just start now?

Hey alex i think he's talking about without touching the throttle, how does it run when you have it Wide open. That one in the video sounds like its bouncing off the rev. lim.