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

[Dean Pappas]

Hello Bob,
Let me see if I can help. The long needle won't do anything. Lengthening the pipe is the most powerful adjustment. I find that the power and level flight speed are best with the pipe set at 24-1/4" from the center of the combustion chamber to the first baffle on the pipe, but the transition gets better at 3/4" longer. Yo may encounter a situation where in level wide-open flight, the engine goes rich. If this happens, go in on the pipe until it just goes away. If your transition has gone to heck again, then here is the "real" solution. Buy the O.S. remote needle valve assembly (I don't have the number) and hook it up to a servo. Couple the throttle into the needle valve with a "curve type" mix, and leave the top and idle percentages as zero. Adjust the middle points to fix the mixture. In your case, that would be the two or three points in the bottom half of the throttle stick range. You want to set the engine as well as you can, with all the percentages zero, then run the throttle to the click closest to each curve point, and adjust the percentage couyple unti you are just rich of peak, and move on to the next. The beauty of this system is that it gives you all the function of the fancy computer carb, with none of the fussiness. The mixture arm has very very little effect near idle, as the almost entirely closed metering slot dominates. This means that engine shake at idle has virtually no effect on idle mixture, even if the arm wiggles some.
 
Oh yes, adding nitro can help, but should be unnecessary. Also a twin plug head helps. I find that I can set the entire curve richer, that way. I use an OS type F in the front hole, and a K&B 1-L in the hotter rear hole.
 
Hope this helps,
Dean Pappas

	----- Original Message ----- 

					From: Bob Harden <mailto:rharden1 at cox.net>  
					To: NSRCA Mailing List <mailto:nsrca-discussion at lists.nsrca.org>  
					Sent: Friday, February 17, 2006 9:26 PM
					Subject: [NSRCA-discussion] OS 1.40 RX mid range loading up problem

					
					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 800! 0 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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