Behind every great flying airplane is a reliable engine with a smooth
transition. To obtain this, you may have to spend some time tweaking the High
and Low End needles that can be found on the carburetor. Personally, I always
start with the factory recommended settings and run the engine first to see if
any adjustments need to be made.
Before we begin, let’s first go over the term “to richen” and “to lean”.
If you want to “richen” a particular needle, you will have to turn the needle
counter-clockwise. If you wish to “lean” a particular needle, you will have to
turn the needle clockwise. Changing one needle adjustment may have an effect on
the other needle adjustment. As a result, take your time.
First, begin by adjusting the High End needle so that you obtain
maximum RPM with the use of a tachometer. Be careful, though, as the engine may
overheat. If you notice that there is any power loss after running the engine
at maximum power, I recommend that you richen this needle about 1/8 of a turn
or so (turning the needle counter-clockwise).
Now that the High End needle is set, it’s time to adjust the Low End.
If you notice that the engine has difficulty transitioning from low power
settings to maximum power and stutters, it may be too rich. On the contrary, if
the engine quits, most likely, it is too lean.
Once the needles are set properly, you should have a smooth transition
from low to maximum throttle.