2-stroke engine sputtering

Ok, after winter, I took my Waverunner out 2 days ago (Tuesday), and
all was well, she purred like a kitten.

Towards the end of my ride (an hour or so, about half a tank of gas),
she did a few little sputs, but nothing to be concerned with that I
thought at the time - I figured hitting a wave wrong, etc.

Well, tonight (Thursday), I could only get to planing speed for about
15 seconds, then the sputtering started.. it's hard to describe, but
it did some low-rpm followed by a couple spurts of high-rpms as if it
was actually going to go.. then back down again.

I'll try to describe it like:
vrrrrrrrrrrrrrrrrrrrVROOMvrrrVROOMvvvvVROOOMvvrrrrrrrrrrrrrrrr

etc.

I opened up the top, but didn't really notice anything. last year it
had similar problems, but it was the water box, and I got that
replaced. I did notice some bluish stuff, almost like foam, coming
from the carb, but about this time it was getting close to a storm, so
I had to bug out and go home.

any ideas before I take it in to the shop?

anything a non-mechanic can try first?

Did you take the air cleaner off to see the carb? Describe the bluish
stuff coming from the carb - it sounds like two-stroke oil (it's blue)
and that perhaps the oil pump line has come loose from the carb
allowing oil to leak. You didn't mention the year of the ski but
when's the last time the fuel filter was changed because it sounds like
fuel starvation at high speeds - there is enough in the system to get
there but due to restrictions it cannot continue to flow enough fuel to
maintain speed - just a guess, you really need to see a competent
mechanic.

Tom