Rotax 447 RPMs Climb - Wont Idle Normally

Hello everyone,
A friend of mine built an ultralight from scratch. He's never flown it
unfortunately due to an engine problem with his 447. When he starts
the engine (which presumably starts fine), the RPM's climb up until he
has to shut it off. It will not idle normally. He's been told that
there is an air leak (?) somewhere, but cannot seem to find the
problem. I believe this engine was brand new when he purchased it.

If you have any leads or advice, he would appreciate it very much.
Unfortunately I don't have anymore details than that as I'm just his
messenger and am not a mechanic of any sort.

Thanks in advance.

Maybe a silly question but . Does he have a prop on it ? Dave





Aaron Jacobson wrote:
> Hello everyone,
> A friend of mine built an ultralight from scratch. He's never flown it
> unfortunately due to an engine problem with his 447. When he starts
> the engine (which presumably starts fine), the RPM's climb up until he
> has to shut it off. It will not idle normally. He's been told that
> there is an air leak (?) somewhere, but cannot seem to find the
> problem. I believe this engine was brand new when he purchased it.
>
> If you have any leads or advice, he would appreciate it very much.
> Unfortunately I don't have anymore details than that as I'm just his
> messenger and am not a mechanic of any sort.
>
> Thanks in advance.

Actually, Terry, you aren't even close. The exhaust stetem of a two
stroke engine acts as a valve via returning pulses and a boost system.
In fact, most two stroke engines will barely run much less gain speed
without an exhaust, " until something breaks".


daranch@epix.net wrote:
> Maybe a silly question but . Does he have a prop on it ? Dave
>
>
>
>
>
> Aaron Jacobson wrote:
> > Hello everyone,
> > A friend of mine built an ultralight from scratch. He's never flown it
> > unfortunately due to an engine problem with his 447. When he starts
> > the engine (which presumably starts fine), the RPM's climb up until he
> > has to shut it off. It will not idle normally. He's been told that
> > there is an air leak (?) somewhere, but cannot seem to find the
> > problem. I believe this engine was brand new when he purchased it.
> >
> > If you have any leads or advice, he would appreciate it very much.
> > Unfortunately I don't have anymore details than that as I'm just his
> > messenger and am not a mechanic of any sort.
> >
> > Thanks in advance.

Aeron,

If the carburettor is mechanically all right, that is if the throttle
slide is moving freely to its lowermost position, you most likely have
an air leak problem. This air leak is located either in the
carburettor, or between the carburettor and the motor, or in the motor
itself (not before the carb or after the motor).
Guide you attention to following items:

Carburettor
Is the throttle cable length appropriate?
Is the idle adjustment screw unscrewed?
Carburettor air screw - Is it unscrewed about 1,5 turns (0,5 - 2,5)?
Carburettor air screw - Is the little O-ring attached properly?
Primer inlet (carb throat) - If there is one and it's not in use, is
it plugged?
Throttle cable inlet - Is it sealed with a rubber cap?
Throttle cable cap - Is the O-ring attached properly?
(Is there a pilot jet properly installed in the carb?)

Carb/Motor
Is the rubber socket between the carb and the motors intake manifold
attached properly and without any air leaks?
Are there any cracks in the rubber?
Are the rubber ring (single carb) and the gaskets for the intake
manifold leaking?

Motor
Is the power inlet/outlet for the fuel pump in use, check line to the
fuel pump, if not - is it plugged?

Are the crankshaft seals, the crankcase half's or the cylinder gaskets
leaking? Confirm with a vacuum leak test. (Less likely on a new motor)


Hope this helps
/Toby