Conference vmszoo::rc

    John, I also have an OS.25 in my Eaglet.  What I've noticed is
    the needle valve setting is very sensitive (at least on mine).
    Once I find the spot with max rpms, I can't vary the setting
    much more than an eigth of a turn before I kill it.
    
    What I do is set to max rpm at idle than give it full throttle.
    Then I fine tune it to get more rpms, this is where I can't tweek
    it much more or it will die.
    
    Ken
    

    
    	Jeez, guys...  Sounds like you guys are really running your
    engines hot!  When you land (not dead stick), can you comfortably
    touch your engine without burning your hand?  Is the stuff coming
    out of the exhaust black?  Any black stuff on your horizontal stab
    that you have to clean after a flight?
    
    	I have an OS .25FSR in one of my planes.  I run it rich enough
    so that the engine stays cool.  Behaves real nice through the entire
    throttle range.  And it comes back nice and cool.
    
    	If you have to demand every little bit of RPM from your engine,
    buy a larger engine and run it richer.  Your engines will last
    longer.
    
    	My 2� worth...

No, mine doesn't run hot...the head and muffler are only warm to
the touch within a minute after shutdown.  I do tweak it by
holding the plane in the air and watching for a dropoff in
rpms...just like the book says.  My instructor this weekend
squoze the fuel line after I got it running a little on the rich
side.  When the rpms dropped, he tweaked the valve until the rpms
stayed even.  I didn't say anything then, but next time I'll hint
that it likes to run a tad rich.  Sounds like you folks are
peaking the engine right up without any problems.

I should mention that the .25 doesn't pull it too swift up here
at 7200 ft.  Any wind above 10 mph or so and it floats around
like one of those puffball things.  I'm using a 9-4 prop; do you
think I should change to something else?  Also, the engine has
only about 45 minutes on it, maybe its not broken in enough???
The instructors have all remarked that it is touchy, requiring
very little control input -- but then again, most of them fly
rockets for their own.  My backup trainer should be a little
better in that regard.

    Never overlook glow plugs when the engine quites only when flown...
    I had that problem on a brand new engine and glow plug. I changed
    the glow plug and everything went fine.
    

Re: .5
<    Never overlook glow plugs when the engine quites only when flown...
<    I had that problem on a brand new engine and glow plug. I changed
<    the glow plug and everything went fine.
 
Interesting observation. It is quite common for the plug on the first run on a
racing engine after a rebuild to quit half way through the flight. This is
caused by contamination of the plug element with aluminum dust. You can wash
the engine and do what you like to clean all traces off machining residue but
it still happens. Could be your problem.

Re the engine quitting the point of this note, sounds to be like you have your 
answer in that you are setting the mixture too lean. A suggestions I have is to 
check the tubing inside the tank for small leaks. If you have small holes 
in it you effectively get a severe case of foaming as the tank gets low and the 
engine then run lean. The thin wall silicon tube as supplied by most tank 
manufacturers is prone to this problem.

John

    Re .0 - Have you tried new fuel, especially if you had this fuel
    through the winter?  Also, start rich, because it will lean out
    as the fuel level gets lower (pressurizing doesn't completely
    counter this).  I had the same kind of quitting problem the beginning of
    this season.  Completely flushing the tank with alcohol and cleaning
    the engine seems to have done the trick, so I think my problem was
    gunk accumulation.

        The only time I would touch the needle valve at idle is if it isn't
    idling properly.  First, adjust the needle valve at full throttle
    to slightly rich.  Then, go to idle.  If you don't get a smooth
    idle, see if you have to go more rich or more lean by adjusting
    the needle valve.  If you have to go lean, crank out the idle air
    screw.  Crank it in to go rich.  But make sure you return the
    needle valve to the setting for slightly rich at full throttle!!!
    Other than that I would NEVER touch the needle valve at idle!!!
    
    Re .4 - I would not use a 10x6 prop on an OS .25.  The people I know
    that have lots of engine experience have said that the harder the
    engine has to work the hotter it will run (at lower RPM's) and you
    probably won't get any more thrust than a 9x6 would give you.  I
    personally use a 9x5 wood or 9x6 plastic prop on my OS .25FP.
    
    Hope any of this helps. Good luck, I know how frustrating it is
    to fight with an engine on a beautiful flying day!  Once you get
    this problem fixed I think you'll find the OS .25 to be a good,
    reliable engine.
    							Bill

Thanks for the nice list of things to check.  I'll go through the
fuel system and try a new glow plug.  The plug in there is a
veteran of the first break-in in my K&B .20; that could've been a
source of contamination.

The fuel is brand-new.  I'm running 5% nitro because of break-in.
I'll go to 10% on the next bottle.  Think I should do that
sooner?  Can I consider break-in to be over by now?

The prop suggestions are interesting; does sound like I should
try a 9-6; the 9-4 thats on there now is just a leftover from
break-in.  I had thought of going to a 10-4 or 10-2 (if one is
made).  Will this have much effect on the way the plane acts in
the wind?  One of the instructors commented that I should try to
shim the trailing edge of the wing up a little to curb the
floating. 

    I'm running a 9 X 6 on my OS .25FP and Sportster 20.  The combination
    is good, and the engine runs well, with a smooth idle.  Are you
    running at elevation?  (Way above Sealevel)?  This might be a factor
    in your sensitivity...
    
    				-Mike