Gasoline Engine Adjustments

Always leave the cowling off until the High and Low End needles are set.


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.

Updated: February 16, 2012 — 3:43 PM


  1. “If you want to “richen” a particular needle, you will have to turn the needle counter-clockwise.”
    Please consider that when you say it like that you are only partly correct as there are carburetors that use air needles, then if one were to follow your statement they would be doing the opposite to the intended result.

  2. Also when talking about gas engines, you may want to add if the pilot needs to pre-set his ‘gasser’ mixture ‘Fat’ or not as apposed to nitro fuel. This would be extremely beneficial in your next article for ‘new-bies’ that are just now starting out in gas.

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