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<DIV>Jerry is right on target.</DIV>
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<DIV>More power generally means more fuel is being burned (or being burned more efficiently) - a tuned pipe on a 2C can do both (add power and/or add efficiency). So when the pipe is added (and tuned) to increase power, the main needle is richened up - and when the engine is "off the pipe" in the midrange, the midrange is slightly richer due to the richer main needle. A common "trap" with the 2Cs is to lean the idle to alleviate the richness in the midrange and this is really only a partial cure.</DIV>
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<DIV>As Jerry noted, lengthening the pipe generally leans the midrange, and adding nitro generally leans the midrange.</DIV>
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<DIV>Good pipe design (and tuning) and concurrent design of the pipe and carb reduce pipe jump and mixture irregularities across the throttle curve.</DIV>
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<DIV>Way back, OS changed (leaned) the fuel metering on the 140RX carb to alleviate a rich spot in the midrange that was popuarly blamed on the carb - this change appeased the majority - but I actually like the original carb better using a longer tune length (compared to the majority at the time).</DIV>
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<DIV>Regards,</DIV>
<DIV><BR>Dave Lockhart</DIV>
<DIV><A href="mailto:DaveL322@comcast.net">DaveL322@comcast.net</A></DIV>
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<DIV>> > -----Original Message----- <BR>> > From: nsrca-discussion-bounces@lists.nsrca.org <BR>> > [mailto:nsrca-discussion-bounces@lists.nsrca.org]On Behalf Of Jerry Budd <BR>> > Sent: Tuesday, March 07, 2006 12:28 AM <BR>> > To: NSRCA Mailing List <BR>> > Subject: Re: [NSRCA-discussion] Fuel Regulation in 2C Engines <BR>> > <BR>> > <BR>> > >5. It is clear that all 2-cycle engines will have this behavior. <BR>> > <BR>> > I guess I have to offer a different opinion on this. If you have the <BR>> > low end set lean (and most running the OS140Rx are running the bottom <BR>> > lean to get the mid-range somewhat reasonable) you will not be able <BR>> &g! t; to get the motor to settle into a low idle quickly. And that <BR>&g t; > presents itself as poor down line breaking, as well as the occasional <BR>> > flameout. When I ran the OS140's I bought four motors and then <BR>> > picked the two with the best carbs (aka midrange) so I could set the <BR>> > low end where it belonged. I also used higher nitro fuel (Magnum #1) <BR>> > to help lean the midrange, which also allowed me to run the pipe <BR>> > about an inch longer (which helped soften the pipe "bump"). <BR>> > <BR>> > I had good luck (post '02 Nats) and good power (8400 rpm, APC 17x12) <BR>> > with the OS's, but I found that the throttle response wasn't the best <BR>> > if you used a lot of throttle to control speed. When I switched to <BR>> > the Webra 160 I was able to set the top end rich and still have more <BR>> > power than I knew what to do with (because of the enormous <BR>> > torque/very conservative exhaust timing), and also set the idle <BR>> > sligh! tly rich so the motor would quickly settle into a low stable <BR>> > idle. Of course this was a lot easier to do with the MC carb since I <BR>> > didn't have to compromise on the mixture settings. <BR>> > <BR>> &g
t; But, anyway, to bring this back to point. The most prevalent reason <BR>> > for a 2c to have an erratic idle with poor down line braking is a too <BR>> > lean idle and a hot motor (like Evil Eric said). Adding a fuel pump <BR>> > or a pressure regulator or whatever won't fix that. <BR>> > <BR>> > Just my $0.02 worth, <BR>> > <BR>> > Jerry <BR>> > -- <BR>> > ___________ <BR>> > Jerry Budd <BR>> > Budd Engineering <BR>> > (661) 722-5669 Voice/Fax <BR>> > (661) 435-0358 Cell Phone <BR>> > mailto:jerry@buddengineering.com <BR>> > http://www.buddengineering.com <BR>> > _______________________________________________ <BR>> > NSRCA-discussion maili! ng list <BR>> > NSRCA-discussion@lists.nsrca.org <BR>> > h ttp://lists.nsrca.org/mailman/listinfo/nsrca-discussion <BR>> > -- <BR>> > No virus found in this incoming message. <BR>> > Checked by AVG Free Edition. <BR>> > Version: 7.1.375 / Virus Database: 268.2.0/275 - Release Date: 3/6/06 <BR>> > <BR>> -- <BR>> No virus found in this outgoing message. <BR>> Checked by AVG Free Edition. <BR>> Version: 7.1.375 / Virus Database: 268.2.0/275 - Release Date: 3/6/06 <BR>> <BR>> _______________________________________________ <BR>> NSRCA-discussion mailing list <BR>> NSRCA-discussion@lists.nsrca.org <BR>> http://lists.nsrca.org/mailman/listinfo/nsrca-discussion </DIV></body></html>