I experienced significant clutch drag and notchy shifting on my Scorpa. 
The oil had never been changed so I put in what I had laying around:
Bel-Ray 80-weight gear lube.  Lotsa drag and sticky shifting.  I then
threw in motor oil, which used to work OK in my Fantics.  Even worse.

Mike Komer of the Trials Shop - the Scorpa importer - suggested I use
Dexron III ATF and much less oil, 400cc verses the 800cc you'd have
trusting the overflow hole.  Well, I finally bought some Dexron III and
tried it and voila!  95% better.  It seems the Rotax can handle very thin
oils quite nicely without clutch surge or squeel.

I don't know why I didn't think of this years ago, but I made a simple
viscocity tester: a small plastic bottle with screw on , conical squirt
end.  I holed the base and cut off the squit end such that I had about a
.140" hole.  I then measured 50cc of oil and timed the gravity pour
through the squirt end with oils at about 65 degrees F.  This simple test
gives a comparison between oils at one temperature...goodnuff to compare
the the effect of an oil on the clutch due to viscocity.

Here are the results in CJ viscocity units (seconds).  Higher time =
higher viscocity.

Bel-Ray Gear Saver 80 weight:   50s (note gear lube viscocity ranges are
different than motor oil)
Valvoline 10W40 motor oil:   57s
Valvoline Dextron III ATF:   26s

I also tested a Chrysler late model spec ATF:

Citgo 7176 ATF:   41s

Notice how the viscocities follow clutch drag.  Motor oil was worst, then
the Bel-Ray, then the Dexron III, which was way thinner and worked.  I
suspect if it was really hot and your clutch chatters and grabs on
release, you could use the 7176 ATF, which is a bit thicker.  Too bad I
didn't have Type F ATF to compare with, as type F is supposed to be
thicker.  Dexron III is the thinnest stuff I've run across yet.

So there you have it.  The solution.  Thanks, Mike.  You were spot on. 
No grabbiness, or chatter.  Neutral is still a pain at  a full stop...it
want to overshoot into second, but this is way better.  I wonder if some
of the drag will return in really cold weather?  I suspect it will.

Not every bike's motor needs perhaps a different oil for optimization.  I
used to use 1/2 85W140 gear lube and 1/2 motor oil (which is way thicker)
in my Fantic with no drag or notchy shifting.

Chris (CJ) Johnson
Director of Engineering,
College Park Industries, Inc.     http://www.college-park.com
(810) 294-7950 (at CPI), (616) 664-4173 (home office)
papazit "at" juno.com