+1 on the jet kit.
I got rid of my flat spot on my 01 by using...
in every fill up.
Around here, 10% ethanol is in every pump.
My bike calls out for 91 octane to began with
and finding higher is tough.
So I took a chance and it worked for me.
There will be those that will argue to facts on
higher octane and the Sta-bil both.
But, it worked out well in my bike.
I installed an ignition advance also (+4°) about
a year before I started using the Sta-bil and
that cleared it up most of the way.
Then the marine Sta-bil cleared up the rest.
I did not want to spring for a jet kit, so I was
looking for an alternative. lol
You might go ahead and look into synchronizing
your carbs if it has not been done in a while too.