OS mixture question

Tue Apr 19 07:27:21 AKDT 2005

This is good info, no doubt!!!
Just a thought - many folks want a "starting point" for pipe length.  Experimenting with different props/pipes and motors - all things being about equal (I know they're not, really, but it's okay), I've found the 17 x 12 APC or similar load starting point to be about 23.75 -24" plug to reflector, following headers curves, and the "wave" length.

This measurement will get a person who's in a hurry in a flyable condition pretty fast, with minimal additional tweaking.  

Of course, YMMV, depending on a lot of things, but the most frequently asked question I get by the newbie two-stroke convert (or a former 2 stroker who has RE-converted)is "what's a good starting point for 1.40 - 1.70's in today's planes?"

Hope this is helpful to someone.

Bob P.
> 
> From: "richard.lewis" <richard.lewis at idmcontrols.com>
> Date: 2005/04/19 Tue AM 11:08:47 EDT
> To: <discussion at nsrca.org>
> Subject: RE: OS mixture question
> 
> Thanks again Wayne...:)  Very well spoken, clear, and concise 2-stroke
> tuning methodology.
>  
> Richard
> 
>   _____  
> 
> From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org] On
> Behalf Of Wayne Galligan
> Sent: Tuesday, April 19, 2005 9:12 AM
> To: discussion at nsrca.org
> Subject: Re: OS mixture question
> 
> 
> I helped a guy with the a similar issue this weekend on his Mintor.   Way
> too lean on the bottom end. His would pop on acceleration or die coming out
> of the outside loop.
>  
> For the OS 1.40 RX Try this:
> Use an OS "F" plug.
> 15% nitro
> I have not had to adjust the pump on any of the OS's I have set up to date.
>  
> Set the top end till it peaks in rpm(use a tach if you have one) and back
> off one click to the rich side.
> Bring it down to an idle and try  to set the idle to about 18-1900 rpm.
>  
> Let the engine idle for at least 20-30 seconds and do not touch the
> throttle.
>    1.  if it speeds up or surges at any time during this time the bottom end
> is lean.
>    2.  if the engine gradually slows down and dies...its rich.
>  
> Advance the throttle with medium speed and observe:
>    1.  if it burbles and picks up speed or burbles and dies bottom end is
> too rich.
>    2.  if it falls flat or hesitates then accelerates or dies it is lean
>  
> This may take several tries to get but once its set then its just minor top
> end adjustments depending on weather conditions.
>  
> Changing pipe lengths will also effect the low end transition.   A longer
> pipe setting will allow you to set the bottom end a little richer and give
> better downline braking.
> I find that running the bottom end as rich as possible with out it loading
> up gives the best downline deceleration.
>  
> Setting your pipe is a whole other story.   My best method is on a test
> stand.   Set the pipe long and run engine, tach the top end at peak rpm.
> Shorten the coupler or pipe about 1/4" at a time and observe the peak rpm.
> It will increase with each shortening of the pipe.  
> Once it peaks in rpm or no longer increases or drops in rpm this is the top
> tuning spot for your engine and pipe for max rpm(not really the desired
> tuning).
> At this point back the pipe off about 3/8 to 1/2".   This will give you a
> good starting point.  I usually lengthen the pipe if I go to a higher loaded
> prop or
> shorten it with a lighter loaded prop.
>  
> The OS 1.40 is a very predictable engine.   If it starts to load up and
> stall in the midrange for no apparent reason or drops rpms 
> after the glow plug is removed first check the plug . If it continues to do
> the same thing then the bearing is probably on its way out.
> Replace the bearing with a sealed bearing or a stainless steel bearing that
> goes in the EFI version.   I have about 200 flights on one
> of my OS's that has the sealed std steel bearing from Bearings Limited in it
> and it is still going strong.   Another way to check the bearing is move the
> prop by the tips
> perpendicular to the engine and if you can feel end play the bearing is
> getting loose.   
> 
> Wayne Galligan
> 
> ----- Original Message ----- 
> From: Kurt  <mailto:kurt at bozarthhomes.com> Bozarth 
> To: discussion at nsrca.org 
> Sent: Monday, April 18, 2005 7:22 PM
> Subject: OS mixture question
> 
> 
> 
> OS 140 RX (non-EFI) question:
> 
>  
> 
> When I advance the throttle, the rpms remain at idle for approx. one second,
> "pop" and then advance to full throttle rpms  I am not quite sure if this
> "pop" and hesitation is a result of having too lean of an idle mixture or
> too rich.  This is an older motor released back when Hobby Services offered
> a free needle valve assembly replacement to correct for mid-range richness
> issues.  I do not know if this was done or not - something I will check for
> tonight.  I have never adjusted the pump setting.  Let me know your
> thoughts.  Thank you.
> 
>  
> 
> Kurt Bozarth 
> 
> 
> 

Bob Pastorello, El Reno, OK, USA
rcaerobob at cox.net
www.rcaerobats.net

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