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<DIV>Dean, Vicente and all,</DIV>
<DIV> </DIV>
<DIV>The high volume arrangement, with pressure up to around 6 psi, was
available from the YS 2 stroke set-up we used to fly 15 years ago. And as I
recall, that arrangement wasn't really much better in fuel delivery than the
better set-ups of today. The 2 stroke still tended to wind up on downlines,
less brakes, etc. BUT, it was a little easier for anyone to play with it and
arguably a bit more reliable.</DIV>
<DIV> </DIV>
<DIV>It seems that it's a built-in characteristic of 2 strokes. I think Dave's
approach of attacking a different part of the power system is a means to an end.
Variable pitch props have been tried before but perhaps it's time to re-visit
them with the programming features available in today's radios.</DIV>
<DIV> </DIV>
<DIV>On the other hand, I might never try it at least in competition.
Although I am a tinkerer by nature, I much prefer KISS for competition
set-ups.</DIV>
<DIV> </DIV>
<DIV>regards</DIV>
<DIV>Matt</DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>In a message dated 3/5/2006 8:31:45 PM Eastern Standard Time,
d.pappas@kodeos.com writes:</DIV>
<BLOCKQUOTE
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue 2px solid"><FONT
style="BACKGROUND-COLOR: transparent" face=Arial color=#000000 size=2>Hello
Vicente and All,<BR>When you put a Perry or OS 140 pump on a carburettor that
was originally intended for suction, the metering slot may be very wrong. The
likely symptom would be mid-range richness. If, and only if, the pump is
capable of delivering substantially more volume than needed, at the desired
pressure, then the loopback method will work, but ...<BR><BR>A restriction in
the return line will increase the pressure, and reduce the surplus volume
requirement. This has been tested! The idea of a needle valve or other
restriction in the return line is a good one, and in the past, I have used a
simple piece of brass tubing filled with solder and drilled out with a small
drill. You could even partially crush the tube with pliers, to get an initial
setting. Keep crushing until the egine runs with the needle valve only a half
turn in from the setting on normal pipe pressure/suction. This still may not
get you the characteristics you desire.<BR><BR>The general rule is that excess
pump pressure means that the needle valve and idle adjustments are set lean,
and the metering slot still leaves you rich in the middle. This is fixed by
lessened pressure, but if a return path is used to reduce pressure, then the
pump needs to be able to deliver much more volume, or the top end needle has
to come out too much, and there will be sporadic leaning. It will make you
crazy. Oh, I forgot: we fly toy airplanes, so the craziness is
fine.<BR><BR>Later,<BR> Dean
P<BR><BR> -----Original Message----- <BR> From:
nsrca-discussion-bounces@lists.nsrca.org on behalf of vicenterc@comcast.net
<BR> Sent: Sun 3/5/2006 8:13 PM <BR> To: NSRCA
Mailing List; NSRCA Mailing List <BR> Cc: <BR>
Subject: Re: [NSRCA-discussion] Fuel Regulation in 2C Engines<BR>
<BR> <BR> John:<BR> <BR>
Thanks for your advice. I already worked the prop. The best I
found is the 3 blade re-pitched. I just want to improve it more.
Probably very difficult task base on the feedback I am getting.<BR>
<BR> I like your idea to tune the return line. I
have been thinking to go that route with a Perry external needle valve in the
return line. The process would be, in the OS 160, to adjust the return
needle valve until the high end needle valve is about 2.5 turns open at full
power. That is the normal setting when I run the engine with no
pump. In this way, we will be close to the original design
pressure. Normally, the OS 160 with the Perry pump sets within 1 to 1.5
turns open. Than means that the pressure is too high. <BR>
<BR> Vicente<BR><BR> --------------
Original message -------------- <BR> From: "John
Pavlick" <jpavlick@idseng.com> <BR>
<BR> Yeah, I tend to agree with Nat here. After
some discussion about the Perry loop idea, I know someone who actually tried
it. It came down to the theory vs. reality thing i.e. "only one way to find
out..." It seemed like a good idea, but it didn't seem to work on our big
motors. I think that in order for this to work properly, you would need a pump
that is capable of way more volume AND pressure than you need. In addition to
this, the regulator should be an external device, not inside the pump like the
way it is with a VP-30, or the internal regualtor needs to have an eaxternal
"return" line. This is how a fuel-injected automotive system works, so it is
possible. The Perry loop thing works for R/C cars and smaller motors but I
think the pump needs more volume to feed our big motors with that big gaping
"hole" in the system (the return loop). Maybe tuning the size of the return
loop wi! th a restrictor would be worth a try. Is it worth the effort?
Generally a VP-30 that is properly adjusted will give reliable performance
with just a vent line and no tank pressure / no return loop. Props have a big
effect on what happens when you return to idle too. If you want to help
downline braking, look at props before you spend a lot of time re-designing
the fuel system. Also, try setting the idle a little bit richer. The slow
transition to idle condition is sometimes aggravated by a lean idle mixture.
Not trying to discredit anyone's theories, just passing along some of my
observations.<BR> <BR>
John Pavlick<BR> http://www.idseng.com
<http://www.idseng.com/> </FONT></BLOCKQUOTE></DIV>
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