Oldie but goodie needs help from good engine man. Engine has good idle
and good top end but is extremely rich in the mid range. Screwed out
the idle screw until the top of the Oring showed. Still rich. Screwed
in the main adjusment valve controlling the pump until the top end
started to slow down. Still rich in the mid range to the point that I
had two dead sticks when I cut the throttle. Obviously something needs
to be replaced but I dont know what part. Just recently the engine was
serviced. The valve head assy was replaced and also the connecting rod
was replaced. Ever since the return the engine had these symptoms. No I
don't want to send it back anymore. Any suggesting before I lay this
engine to rest
Call the engine shop and talk to them.
They may recognize the symptoms.
I am NOT a "good engine man." I'm currently climbing the
learning curve with a YS 91 AC.
At the pattern nationals, I overheard a YS guru telling
a sponsored competitor that he had an extra backup engine
waiting for him in the car. Jason Shulman had a YS engine
quit on him early in his first semifinal flight. He
switched to electric for the rest of the competition (and
I've heard it said that you need three YS engines to be
-- one in the plane
-- one in your field box
-- one on its way to or from the engine clinic
Heh heh heh... we've all been there! I take objection to your last line
though..... while YS motors can be fussy beasts to get setup, once they're
set they run forever. case in point, my 120SC hasn't had a prop, plug, or
needle setting change in FOUR YEARS. (Yes, it *WAS* flown multiple times
each summer!) A big part of the trick is to run the right fuel (I use a
blend called YS-20/20 that has 20% nitro & 20% oil), don't EVER touch the
pump delivery adjustment screw, and make all your needle settings at an
IDLE, then run it up to full speed for e few seconds & idle it back down.
(This allows the pump pressure to equalize)
Put strapping tank around your fuel tank.... it *WILL* rupture someday.
Secure all your fuel lines with clamps / wire
Use different color tubing for the feed / pressure lines to prevent reverse hookups.
DON'T RUN IT LEAN!!!!!
Double nut your prop, especially with APC props.
Use aluminum spinners, they run truer than plastic.
Other folks advise buying "Leak Free" gaskets and replacing
the gaskets EVERY TIME you open up the engine.
And I've heard other stuff that I haven't written down
about pump spring maintenance and the like.
Call the experts. It won't cost you a lot and the worst
case is that you feel happier about turning your YS into
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