Discussion:
YS 120 SC Engine
(too old to reply)
rgtoth
2007-08-10 02:04:14 UTC
Permalink
Oldie but goodie needs help from good engine man. Engine has good idl
and good top end but is extremely rich in the mid range. Screwed ou
the idle screw until the top of the Oring showed. Still rich. Screwe
in the main adjusment valve controlling the pump until the top en
started to slow down. Still rich in the mid range to the point that
had two dead sticks when I cut the throttle. Obviously something need
to be replaced but I dont know what part. Just recently the engine wa
serviced. The valve head assy was replaced and also the connecting ro
was replaced. Ever since the return the engine had these symptoms. No
don't want to send it back anymore. Any suggesting before I lay thi
engine to res

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Martin X. Moleski, SJ
2007-08-10 16:47:23 UTC
Permalink
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
won).

I've heard it said that you need three YS engines to be
competitive:

-- one in the plane
-- one in your field box
-- one on its way to or from the engine clinic
Marty,
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
a doorstop.

Marty
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42etus
2007-08-10 17:51:49 UTC
Permalink
<Any suggesting before I lay this engine to rest


Sure, send it to me. I can use it as "nose weight " in my next plane. <grin>

Seriously, give Central Hobbies a call. You've got nothing to lose and
everything to gain.
42
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R.A.Gareau
2007-08-12 20:43:23 UTC
Permalink
Unscrewing any needle will always creat a bigger passage thus making
possible for a richer mixture,
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
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rgtoth
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Martin X. Moleski, SJ
2007-08-13 03:51:42 UTC
Permalink
Unscrewing any needle will always creat a bigger passage thus making
possible for a richer mixture,
Unless it covers an air bleed hole, in which
case unscrewing the needle admits more air and
leans the mixture entering the combustion chamber.

Marty
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OldPhart
2007-08-13 14:14:36 UTC
Permalink
"Martin X. Moleski, SJ" <***@canisius.edu> wrote in message news:***@news.supernews.com...
| On Sun, 12 Aug 2007 16:43:23 -0400, "R.A.Gareau" <***@supernet.ca>
wrote in <ahKvi.291$***@wagner.videotron.net>:
|
| >Unscrewing any needle will always creat a bigger passage thus making
| >possible for a richer mixture,
|
| Unless it covers an air bleed hole, in which
| case unscrewing the needle admits more air and
| leans the mixture entering the combustion chamber.
|
| Marty

Unless it is an idle ajustment of the fuel, like the old fox two needle
valve carbs. In fact, Fox published how to adjust the mid range by
changing the contour of the needle valve point. Not all carbs adjust the
idle by airbleed. I only own one engine that does, an OS FP 40. The rest
require opening the barrel for idle air and then adjusting the idle
needle for proper fuel.
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jd_3010
2012-12-04 19:03:38 UTC
Permalink
Hello, I have five of these monsters, they are
livid, with hatred and horsepower, laughing..
You must at least run YS 20/20 fuel with these,
other cheaper less nitro and oil, will kill them,
make them run even worse.. They were a hotrod
racing pylon type engine.. They don't run well
in the mid-range, as they were designed to be
at idle or full throttle.. If memory serves me right,
I ran a APC 16X8 and it would over swing it.. Tach it
wide open throttle to 9200-9500 rpm max, as in a dive
it'll surpass the 10 thousand rpm redline.. pull back on
throttle in a dive, better yet.. Guy's with 140's, I'd torment
them with my SC... SC's were not user friendly, the SF 120
is the user friendly version.. Definitely, doulble nut the prop~!~'
these monsters will throw a prop, about 100 yds. if it gets loose
while at full throttle, on the ground. I also ran the little slip o
air
cleaner on mine, didn't bother the engine at all, in fact, improved
the mid-range, just a smidgen... I still have all my SC's, floating
in after run oil, stored away for another day, when I decide to fly
again. Fallin' back into vintage trail bikes for now... Hope thi
helps

--
jd_301

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