YS 120 SC Engine

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

-- rgtot

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rgtoth
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On Thu, 9 Aug 2007 21:04:14 -0500, rgtoth wrote in :

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

But a friend wrote me:

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

Reply to
Martin X. Moleski, SJ

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R.A.Gareau

On Sun, 12 Aug 2007 16:43:23 -0400, "R.A.Gareau" wrote in :

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

Reply to
Martin X. Moleski, SJ

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.

Reply to
OldPhart

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 on 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 this helps.

Reply to
jd_3010

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