[NSRCA-discussion] OS 1.40 RX mid range loading up problem

[AtwoodDon at aol.com]

I was having similar problems 2 years ago and finally resolved it by going  
to a mixture control carb which worked very well.  However, the problem  
returned when I went to a new plane and did not want to use the mixture control  
carb on a new setup with a new plane.  I was able to resolve most of the  problem 
by lengthening the pipe in 1/2 inch increments until the transition  smoothed 
out.  I resolved most of the problem but still had a some gurgle  in 
transition.  I was running Magnum #1 and an APC 17x12.  After some  conversation with 
Lance Van Nostrand (AeroSlave), he suggested I reduce the  compression 
somewhat by adding a head shim, or reduce the nitro to 15%.  I  tried the head shim  
and my problems mostly disappeared. After  that, I went to an AeroSlave pipe 
and my problems went away completely.  It  transitioned cleanly through out a 
flight and had a nice mellow sound, more than  plenty of power for a 9 3/4 
pound plane.  It runs very well on either 15%  or Mag #1 now.
 
Every condition is different and I don't know if any of this will  help.  I 
would suggest the 10% nitro might be a little light for the 16x14  prop.  Have 
you tried any higher nitro?
 
Don  
 
In a message dated 2/17/2006 6:28:55 P.M. Pacific Standard Time,  
rharden1 at cox.net writes:

 
Hello All,
 
I need some of your expertise.  I am having  trouble with my OS 1.40 RX 
loading up in mid range.  The engine has  5 flights and approx 2 gallons of fuel 
through it.   I am  using an APC 16 x 14 prop,  OS T-6010 Tuned Silencer, tried 
the A5,  #8 and type F plugs (no difference), Magnum fuel 10% nitro with 
caster/synth  blend, pipe set for 8000 rpm, and using the short needle valve.    
The low end idle adjust screw is adjusted all the way to the lean (all the way  
in) which is necessary to idle smoothly.  Transition quickly from idle to  max 
throttle isn't too bad but slower than I would like.  If  I set the throttle 
at 30% to 50% it loads up and and slows in  RPM.  In transition from mid to 
high throttle  the  engine vibrates and burbles for 3 -4  seconds before  it 
clears and comes on the pipe, it has even stopped running a few  times.  I have 
read that some folks use the longer needle valve and  higher nitro to minimize 
this problem, but I haven't tried that yet.   From those of you who have 
experience with this, what is going on,  and what are my  options?



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