From: bill@c3177208.ssr.hp.com (Bill Chidester)
Subject: Re: Responses from Engine troubles
Date: Tue, 18 Aug 1992 03:03:43 GMT
Organization: Hewlett-Packard, Orlando Fl.
X-Newsreader: Tin 1.1scd1 PL4

jam@ee.uwm.edu (Jeff McKelvey) writes:
: 
: I recently posted a question about a problem I had with an OS SF .25.
: It would run fine on the ground but after 3-5 mins in the air it would
: suffer a severe loss of power and RPM.  Here is a brief list of the
: possible solutions I recieved:
: 
  (stuff deleted...)

: noticed that the engine reaches peak RPM when the needle valve is about
: 6 turns out, from the responses I've been getting and from the manual
: this seems like a lot, is it?  Should it be closer to 2 or 3?
: It's been raining here all week so I don't know how the engine works in
: the air yet but, as usual, runs great in my parking lot.
: 
: Thanks again,
: Jeff
: 
: 

   You still have a whopper of an air leak and I'll bet I know where it is.
   Every O/S engine I have seen (well, every two-cycle engine) leaks around 
   the needle valve.  Our standard fix is to put a short (1/4 to 3/8") section 
   of medium or large fuel tubing over the needle valve, where the needle 
   valve screws into the needle valve housing.  Use a small hemostat or a pair
   of 'streamly skinny, very expensive, needle-nosed pliers.  If you don't have
   any hemostats, by all means get some.  Ask your dentist if you can buy some
   of his worn out ones and he'll likely give them to you.  You may have to 
   take the little spring steel needle valve keeper off in order to do this
   (that's the thing that goes ticky-ticky-ticky whenever you turn the needle
   valve).  The fuel tubing will keep the valve from turning in addition to 
   providing a good seal.  (Note that there are many Chinese/Korean engines on
   the market that are OS knock-offs that suffer from the same problem.) 

   Most O/S engines will go from rich to lean between 2.5 to 1.5 turns and 
   should go from lean to rich in one turn.  If you have to go more than a 
   couple of turns for a rich run, check for air leaks or look for some sort of 
   fuel restriction (detach the fuel feed and the pressure feed, blow into
   the pressure line -- point the feed line away from your face.  You should
   get a good stream of fuel with a moderate toot on the pressure line.  If
   your cheeks puff out, you've proably got a crimp in the line).  As a matter
   of fact, the only two cycle engine I own that doesn't leak around the
   needle valve is a Picco .45.

   One of the most perplexing engine problems we've seen recently (our flying
   club is 'we', I doubt they'll ever elect me Pope) was an OS .40FP that
   behaved exactly as you described.  Ran on the ground, but no more that 3
   minutes in the air.  It was noted that the needle valve was very "touchy"
   and sensitive to sideways pressure.  A sure indication of a bent needle. 
   The valve looked good, but was replaced anyway, to no avail.  Finally, it
   was found that the needle valve was fine, but the casing had been bent
   during an unexpected density transition (from air to Earth).  A new needle
   valve casing solved the problem.

   Let me know how the tubing trick works out -- it's cured many an OS engine
   of lean running.

 -------------------------------
   Bill Chidester   KE4WS
   Sunset R/C (Home of the Cloud Dancers)
   bill@c3177208.ssr.hp.com