High-speed needle O/S carburetor. Low-speed needle (seat) I/S carburetor.

Start the engine, give it full throttle and adjust the high-speed needle until the engine reaches its highest rpm (peak). Then back the needle out about a quarter turn or so to richen it a little. With the glow igniter still attached slowly close the throttle to a point where the engine idles at a reliable rpm without dying. Then remove the glow igniter. If the engine dies immediately it's too rich, so you should lean it by screwing in the low speed needle 1/8th turn. (Don't touch the high-speed needle).

Re-start the engine and give it full throttle to remove any excess fuel in the crankcase. With the glow igniter still attached slowly close the throttle to a point where the engine idles at a reliable rpm without dying, then remove the glow igniter. This time the engine may run a little longer before dying, if it does then turn the low speed needle in another 1/8 turn. Start the engine apply full throttle to remove excess fuel in crankcase and with the glow igniter still attached close the throttle to a point where the engine idles at a reliable rpm without dying. Remove the glow igniter and notice if the engine rpm drops a little when you remove the glow igniter but keeps running, if so we’re getting close. It’s still too rich and you can prove this by starting the engine, opening up the throttle to see if it “blubbers” and dies. This happens because excess fuel collects in the crankcase during rich idle. So when you open the throttle all that excess fuel is sucked into the cylinder making the mixture way to rich for the glow plug to ignite it.

Keep leaning the low speed needle until it idles well but instead of it blubbering and dying when you apply full throttle, it hesitates but continues to run. If this happens you’ve leaned it too much and you need to richen it some by turning the low speed needle out 1/16 turn. Crank it up and try it again. The low speed needle will be set correctly when you can fire it up, remove the glow igniter and the rpm doesn’t change at all. And when you open up the throttle it doesn’t blubber or hesitate, it just runs.

The final thing to do is re-adjust the high-speed needle. Crank the engine and open up the throttle. Turn the needle until the highest peak rpm is achieved and then richen it a little by turning the needle out 1/8 turn. (The fuel mixture can change in flight as you point the nose up and as the fuel level in the tank decreases. In both of these cases a leaner fuel mixture occurs so we adjust for this by setting the mixture a little rich.)

Start the engine, remove the glow igniter and advance the throttle to full open. Pick up the plane and raise the nose to at least a 45-degree angle. If the engine hesitates a bit then you need to richen it a little more by turning the high-speed needle out 1/16 turn. Try it again and when you can point the nose up and it doesn’t hesitate but instead gains a few rpm’s then you’ve got it adjusted right.

Question: Where should the throttle trim setting be while performing this action – neutral, down or up?