Model Forum / Radio Controlled / Air Models / April 2004

Had the same problem with a YS120NC. It would run all day mounted on a stand
on the ground, but quit at part throttle in the air. That one was fixed by
trading up to a YS120FZ. Since your engine ran well before, could be a lot
of things.

Engine:
You mentioned it happens a part throttle only, the midrange is probably be
loading up, cooling the engine to the point where it will not fire, kind of
like turning off a light switch (I used that same description when
describibg the problem with my 120NC). Might be a worn diaphram and fuel
plunger, or the low end needle is too rich. It is an air bleed type, in is
richer, out is leaner. You check it at idle. If it speeds up, it's lean,
slows down, it's rich. You could also try going in half a turn on the
regulator. Reset your high speed and idle needles.
How was the engine oriented in the previous plane? Upright? Inverted? Side
Mounted? Did this orientation change in the new plane?
Did you try a new glow plug? OS "F" is a great plug for YS engines.
Is it a "high mileage" engine? Blowby past the piston can cause midrange
troubles.

Plane:
Could the tank clunk in new plane be folding over?

Put in a new regulator diaphagm.....couple of bucks and it'll be fine.
If you have adjusted on the regulator pressure screw, return it to
where it is flush with the housing.

Phil AMA609

Are you running 20% or more nitro?  20/20 blend is what they were designed
for.

Have you replaced the glow plug lately?  I know that they are so reliable
that you often forget to replace them for a year or two!

Also, check the diaphragm for distortion.  If it is still flat, it is OK.
If it is bulging even a little it may become unreliable.

--
Paul McIntosh
http://www.rc-bearings.com