[NSRCA-discussion] Fuel Regulation in 2C Engines

[Jerry Budd]

>5.  It is clear that all 2-cycle engines will have this behavior.

I guess I have to offer a different opinion on this.  If you have the 
low end set lean (and most running the OS140Rx are running the bottom 
lean to get the mid-range somewhat reasonable) you will not be able 
to get the motor to settle into a low idle quickly.  And that 
presents itself as poor down line breaking, as well as the occasional 
flameout.  When I ran the OS140's I bought four motors and then 
picked the two with the best carbs (aka midrange) so I could set the 
low end where it belonged.  I also used higher nitro fuel (Magnum #1) 
to help lean the midrange, which also allowed me to run the pipe 
about an inch longer (which helped soften the pipe "bump").

I had good luck (post '02 Nats) and good power (8400 rpm, APC 17x12) 
with the OS's, but I found that the throttle response wasn't the best 
if you used a lot of throttle to control speed.  When I switched to 
the Webra 160 I was able to set the top end rich and still have more 
power than I knew what to do with (because of the enormous 
torque/very conservative exhaust timing), and also set the idle 
slightly rich so the motor would quickly settle into a low stable 
idle.  Of course this was a lot easier to do with the MC carb since I 
didn't have to compromise on the mixture settings.

But, anyway, to bring this back to point.  The most prevalent reason 
for a 2c to have an erratic idle with poor down line braking is a too 
lean idle and a hot motor (like Evil Eric said).  Adding a fuel pump 
or a pressure regulator or whatever won't fix that.

Just my $0.02 worth,

Jerry
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Jerry Budd
Budd Engineering
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