Rotax 912 questions

Hi all.

I have recently completed my airplane and have begun taxi testing. For
an engine I chose the Rotax 912. I purchased the engine from a
Trade-A-Plane ad where it was advertised as being "new in the box".
When I inspected the engine prior to buying it did appear to be brand
new and was still bolted into the shipping container. I bought the
engine in 1999 and it has not been run until recently. Not only that,
but the serial numbers indicate that the engine was 5 years old in
1999. The age of the engine probably does not matter, however, I
mention it only as background information.

I have been happy for the most part with the engine. But there are some
odd things about it. I have no experience with 912's so I thought I'd
seek some wisdom from others. First, the engine has an incredible
amount of gearbox chatter at around 1600 all the way to about 1950 RPM.
It's swinging a large 72" wood prop. I have set the idle to 2000 RPM in
an effort to get out of the gearbox chatter zone, but with a 72" prop
that still results in quite a bit of thrust. In other words, when I
chop the power on landing (when I get to that point) I'll still have a
bit of power pulling me along. Is that normal? Also, I know the 2
stroke Rotax's are notorious for gearbox chatter, but you don't hear as
much about that from the 912. Is my engine behaving normally? What are
others doing to deal with the chatter?

The other unusual thing about the engine is that it is very cold
natured. It takes a very long time for the water temp to come up. I've
even gotten to the point of covering up half the radiator with a piece
of cardboard until the temperature comes up. I'm starting to suspect
that perhaps I have a thermostat that is stuck open (perhaps due to the
prolonged time in storage). Is that reasonable or is that normal
behavior for the 912 ?

Thank you in advance for any help or advice you can offer.

- R. Parsons