From: sbixby@cup.portal.com (Steven W Bixby)
Newsgroups: rec.models.rc
Subject: Re: Responses from Engine troubles
Date: Mon, 17 Aug 92 10:12:01 PDT
Organization: The Portal System (TM)


<details about OS 25SF problem solving deleted>

>After doing the above, a couple of more questions have come up.  First of
>all, what is 2 cylcing and 4 cycling?  I didn't realize a 2 cycle engine
>was capable of 4 cycling.  How do you tell the difference?  Also, I

This is mainly an expression to describe your two-stroke sounding like it's
missing some firing cycles, which it is.  This happens when you richen up
the mixture to the point that it sounds like the engine is 'bubbling' with
an inconsistent firing pattern - when you lean it out past the point where
it stops 'bubbling', it fires on every stroke and sounds much smoother.  It's
pretty intuitive after the first couple of times running the engine.

>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?

Six turns out seems like WAY TOO MUCH, in my opinion - disassemble your
carb again and look for grit.  1.5 to 2 turns should be all you need.  I 
have the OS 32F, which I think (?) has the same carburetor, albeit with
a larger bore.  With this, the needle is only out about 1.75 turns and
the setting is fairly sensitive - 5-10 clicks of rotation is more than 
enough to go from too rich to too lean.

Being nearly deaf, I have more need for it, but you should consider getting
a tachometer, and use it to judge the mixture needle adjustments.  Lean it
out to top RPM and then richen it up to about 2-400 rpm less than top for
flying - especially when on the ground and with a full tank.  It'll lean
out slightly in the air and when the tank level lowers.

As far as needle settings go, you need to juggle the needles until it works
right.  My procedure is as follows, AFTER break-in and several tankfuls in
the air:

1:  Start and warm up engine - go to full throttle and set the main needle
    to top RPM and richen to 2-400 rpm less than top.

2:  Go to idle and use trim to set a normal idle (2500 rpm for a .25).  Wait
    to see if the engine quits, and observe how it quits - if it runs rich
    for a bit then leans out and quits, your idle needle is too rich.  If
    it seems to run fine for awhile, pinch the fuel feed and wait til the
    engine almost dies - if it speeds before going dry, then you're too rich.
    My goal is to set the idle needle such that I pinch the tube and it takes
    about 5 to 10 seconds for the engine to speed up.

3:  Repeat steps 1 and 2 alternatively until you are happy with the settings.
    The goal is to have a good slightly-rich top end, and an even, steady
    idle, and a good transition from idle to full.  If the transition is
    sure and just very slightly hesitant, you're settings are right on.  If
    it bogs down for a few seconds when you throttle up, it's too rich on
    idle, and if it goes lean and almost dies on throttle up, it's too lean
    on idle.

It should take about 4-5 trips through steps 1 & 2 to get a perfect setting.
Since I always understood how to set the things, I NEVER had problems with
my engines running strangely that was due to carb settings - unfortunately
that meant that I ended up setting everyone else's carbs too - plenty of
earaches and less flying time.  :-(  But that's ok.

So, if you actually got this far down in this post, congratulations! ;-)

Good luck!

  -swb-  (Steven Bixby - sbixby@cup.portal.com)
Newsgroups: rec.models.rc