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<P>David - </P>
<P>It's already been mentioned, but I'd guess the culprit is rich bottom end / idle. (It should idle at around 1800 now, and after another gallon or two it should idle reliably at below 1700.) I found that after setting my idle on a test stand w/ the engine upright, the idle always goes way rich when the engine is inverted in the plane. The idle cam / adjustment is sensitive - a little movement changes a lot. </P>
<P>Pipe length might be an issue with the throttle response you mention - nothing til 1/3 then no change at the top of the throttle stick. I couldn't tell the length from the plug or exhaust flange to the pipe baffle, but it might be worth it to pull the pipe out 1/2" - 1" and see if that helps your throttle situation. </P>
<P>Lots of guys are flying the 16x12 or 16x12W props, but I also had good success w/ a 17x10 (fullblade) - engine turns up a little better, maybe better braking, excellent vertical, maybe better speed control. </P>
<P>All that said, the engine really handles like a big, powerful sport engine - no bad habits at all that I know of. </P>
<P>Enjoy - </P>
<P>Rick </P>
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<DIV></DIV>From: <I>"David Flynt" <dflynt@verizon.net></I><BR>Reply-To: <I>NSRCA Mailing List <nsrca-discussion@lists.nsrca.org></I><BR>To: <I><nsrca-discussion@lists.nsrca.org></I><BR>Subject: <I>[NSRCA-discussion] First day out with OS 140RX (somewhat long)</I><BR>Date: <I>Wed, 01 Mar 2006 16:40:37 -0800</I><BR>>Today was one of those beautiful California days, in between the rain, and I<BR>>have the week off, so I finally got my ZNline Supreme in the air for several<BR>>trim flights. Also, I switched from the Webra 160 with M/C to the OS 140RX.<BR>>Below are my initial impression of OS, along with comparison to YS 140DZ:<BR>><BR>>I was particularly careful while breaking in the OS. I wanted to ensure no<BR>>problems, and the engine was ready for fly time. I
broke in on the bench<BR>>with one gallon of fuel. I saw 7800 rpm with a 16.5x12w prop mounted in the<BR>>plane today, fairly rich. I'm hoping I have it set way too rich, and that<BR>>it will gain more power as I get more fuel through it. My setup is a Karl<BR>>Mueller header at 9 3/8 inches from from exhaust flange to the entrance of<BR>>the pipe, and an ES 2C140M80 muffler. Cool Power 15%. The Mueller header<BR>>has a sharper rise over the OS or Hatori header, and I needed that to clear<BR>>my firewall. Total length due to the sharper rise is near the same as the<BR>>stock OS header. What a nice header BTW. It has the right thrust built in<BR>>so it is straight down the middle of the pipe tunnel. It came with a short<BR>>extension so that there is stress
relief on the header to prevent it from<BR>>breaking.<BR>><BR>>Big two strokes are new to me. Before this engine, I was running a YS<BR>>140DZ, and before that, YS 120 - 140. Here are my initial observations and<BR>>comparison between the 140DZ and 140RX:<BR>><BR>>Ease of use: Probably a toss up. The OS is very user friendly, and is<BR>>simple, and runs on sport fuel. It is not as easy as the YS in that you<BR>>need to tune header length and select optimal prop and muffler/pipe, however<BR>>for the OS you can stand on somebody else's shoulders, and that is what I<BR>>did for the most part. I don't know if I am done tuning it however. Both<BR>>engines are pretty much hands off once broken in and set (at least what I<BR>>hear for the OS). I flew 300 times with the
DZ, and never touched the<BR>>settings after break in.<BR>><BR>>Ease of start: Hands down, OS. This engine starts with ease. The DZ, once<BR>>you learn it, will start easy so long as you have a strong starter and<BR>>strong glow source. But it can lock up on you if you allow it to flood.<BR>><BR>>Idle: Definately the OS. I had a good idle after one gallon, and I still<BR>>have not touched the low end from factory setting. The YS will idle ok for<BR>>a while once warmed up, but it won't idle forever. It does not really<BR>>matter so long as you do not let it idle for long periods.<BR>><BR>>Reliability: No way to know since I don't have time on the OS, but one<BR>>strike against it today. It flamed out at the bottom of the
reverse<BR>>avalanche. I just made it back, heart pounding all the way. This is<BR>>probably an anomaly, and I only have 1 1/2 gallons through it (I should not<BR>>have been practicing the reverse av with such little time on the engine, but<BR>>oh well). Idle speed was 2000 on the ground. On the first flight however,<BR>>I overshot the runway twice, and I had to go around. So, it stayed lit when<BR>>it counted. The DZ never flamed out during flight. I speculate that the DZ<BR>>is more reliable, but I am splitting hairs.<BR>><BR>>Quietness in the air: OS is quieter, like a whisper compared to the DZ. DZ<BR>>has a lower pitched noise.<BR>><BR>>Vibration: OS is much less vibration and very smooth at idle through
full<BR>>thottle. There is an area about 1/4 throttle where it shakes a little, but<BR>>not bad compared to the DZ. The 160DZ I hear is a lot smooother than the<BR>>140DZ, which would be nice.<BR>><BR>>Torque: Hands down, the DZ. The DZ has a smooth, linear throttle curve and<BR>>usable torque at any throttle setting. This is what is so great about the<BR>>DZ. The OS is fairly limp and useless until you get past 1/3 throttle. At<BR>>half throttle it comes alive, and at 5/8 throttle to full throttle, there is<BR>>little difference in output. I think this is one of the major differences<BR>>between two cycle and four.<BR>><BR>>Power: The OS does ok, but the DZ is far more powerful. Maybe I need more<BR>>time on the OS before a fair
comparison. I have a gut feeling however, from<BR>>running this and watching other OS owners over the years, that the DZ<BR>>dominates in power.<BR>><BR>>Weight: OS with ES muffler is probably 3-4 ounces lighter than a DZ with<BR>>similar muffler. But I think the DZ might be equivalent weight with a<BR>>Hatori short pipe. Not sure.<BR>><BR>>Fuel requirements: DZ runs best on one type and brand of fuel: Cool power<BR>>30% heli. This is expensive stuff, and is my major gripe with the DZ. The<BR>>OS ran outstanding with 15% sport fuel. For economy, you cannot beat this.<BR>><BR>>Smoke trail: DZ has a thick smoke trail with CP 30%. This OS had fair<BR>>amount of smoke, but I expect it to decrease as I lean in. None of OS'
that<BR>>I see at contests have a heavy smoke trail.<BR>><BR>>Overall preference: This is a little tough because the DZ performs better<BR>>for pattern, but the OS is probably good enough. Greg Frohreich flies very<BR>>well with his OS, and until I can fly better, I wonder if I need a better<BR>>engine. Still, the DZ is a pleasure to run, with exception of the expensive<BR>>fuel. I choose the DZ as my preference, but I like the OS for the positive<BR>>characteristics I mentioned.<BR>><BR>><BR>>David<BR>><BR>>_______________________________________________<BR>>NSRCA-discussion mailing list<BR>>NSRCA-discussion@lists.nsrca.org<BR>>http://lists.nsrca.org/mailman/listinfo/nsrca-discussion<BR></FONT></BLOCKQUOTE></div></html>