submikester....
....I think I can simplify this for you....
My problem isn't the top end or the low end but the mid range. It will
run fine at the top end, well at the bottom but when I pick the nose up at half
throttle or so it leans out something terrible.
....any time our aero-model engines "lean out" when the nose is raised, it
is caused by one thing....and one thing only.....lack of fuel pressure. It doesn't
really matter if it is suffering from lack of fuel on the low end (idle mixture), or
the top end (high speed needle)....if the engine is leaning out, it is from lack of
fuel. This reality is simple.
Keep in mind, there are only two "adjustments" on the GMS .47....the low and
high speed needle adjustments....there is no "mid range" adjustments. We all
know that the low speed needle adjustment, and the high speed adjustment
effect the mid range....but, even if the low speed is set slightly rich (the
way I like it) and the high speed is set richened for flight....when you get to the
mid-range....in a "stand alone mode"....the mid range is kind of "on it's own".
You cannot richen the low speed enough, or the high speed, because you will
be outside the parameters on both ends, meaning....if the fuel pressure is not
enough....you will not be able to compensate by over richening either end of
the spectrum....rather, performance will suffer to the extent that the mid-
range won't really matter.
When you go out of the low needle spectrum, and are advancing into the high
speed needles influence....there is only one thing that is controlling that portion
of the mixture, and that is the
taper of the needle, working in conjunction
with the design of the nozzle.
Another thing to keep in mind is....the low speed needle adjustment isn't really
a "fuel circuit"....it is simply a method of "blocking off" the fuel mixture provided
by the needle/nozzle combination from the high speed needle. This of course
relies on the principle that the needle/nozzle relation is
perfect at all settings,
and it also assumes that the fuel pressure is constant, or at least satisfactory.
This is of course, may not the case.
This is the main reason the YS engines are so succesful. By utilizing their super
high pressure fuel systems (enough to blow some fuel tanks in half) the engine
will not "lean out" in any case. The fuel pressure is more than adequate
to eliminate the leaning-out problems associated with the rest of the aero-model
engines (non pumped) no matter what the throttle setting, no matter where the
tank is mounted, no matter how much fuel is in the tank....or no matter what
attitude (position) the airplane is in.
The bottom line is....fuel pressure is not that great at half throttle...less than at
full throttle, to be sure. Were you planning on going verticle at half throttle ? If
the engine is leaning out on the ground at half throttle, you must address this
problem.
When I started looking at my engine for possible problems, I noticed that the
nipple on the muffler had flasihng in it....it wasn't drilled properly, and probably
wouldn't have delivered full pressure to the tank. That was the first thing I did
....was remove the restriction from the exhaust nipple....
....check yours. If you aren't getting proper pressure to the tank, all bets are off.
FBD.
