Radio Control Engines
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Nitro Engines for RC Cars, Airplanes and Boats |
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HOW TO TUNE THAT AIRPLANE TWO STROKEThis article is about tuning a engine not breaking one in, so we will assume that the engine has already been broken in. Some people have a lot of trouble getting a engine to run smooth and transition from idle to full throttle while others make it look easy. A few act as if it is a secret talent that they have been born with. I guess they think it makes them look smarter than the rest of us. It is no mystery at all and only takes a few minutes. Before you connect the glow starter, open the needle valve about 3 turns, choke the motor with your finger on the intake and slowly hand crank the motor until you have fuel in the carburetor. Don't overdo it or you will flood it, just 2 or 3 flips should be plenty. When you have fuel attach the glow starter and flip it until it starts. If you see raw fuel coming out of the exhaust, it is flooded. Take out the glow plug and flip it several times to clear the excess fuel and close the needle down and start over. When it starts, throttle it up to full throttle, it should be very rich and running a little rough. Slowly, lean it out until the RPM comes up. Doing it slowly gives the engine time to burn the excess fuel in the crankcase. When it starts to run smooth, continue to lean it a little at a time until the RPM starts to fall off or slow down. When you reach this point it is too lean. Back it up (richer) a few clicks on the needle until the RPM comes back up then stop for a few seconds. When it is running smooth again open the needle 2 or 3 clicks richer and give it a few seconds. Now pinch the fuel line just before the carburetor and let it go quickly. Don't hold it closed just pinch and let go. If it is right, the RPM will pick up just a little then come back down. If it stops running, or even tries to, then it is still to lean, open it up a bit more and pinch again until you get that momentary increase in RPM. If it does nothing when you pinch it, it is too rich and you need to lean it out some more. Do things a little bit at a time and give the engine about 10 seconds or so to settle in to the new setting before you pinch the fuel line. When you have it where you think it is right, you should then hold the airplane pointing straight up or nearly so and listen for a change in the RPM. It should hold steady with no change. Give it about 10 seconds or so in this position. When it is running smooth at full throttle it is time to set the idle. I find this is what trips most people up more than anything else. This setting is just as easy. When properly tuned the engine should come from idle as soon as you move the throttle from idle to full throttle, with no hesitation. If it stutters and sounds like it is missing or running rough but finally comes up to speed then the idle is too rich. If it dies or hesitates when you advance the throttle it is most likely to lean. Make small adjustments and give the motor at least 20 seconds at idle before you advance the throttle. It is strictly a trial and error process with small changes and checks between changes. Remember it will take at least 20 seconds for a change to have any effect when the motor is at idle speed. This is because of unburned fuel in the crankcase that needs to be burned off. When you get it right try the point it up trick again. It should run smooth at either idle or full throttle and the transition must be smooth with no hesitation. If while flying, the engine seems to slow down even though it is at full throttle, cut the throttle back and land as soon as possible, the engine is too lean. The settings will change in the air, and if you are too close, when you take off it can go too lean in the air. After you get it right on the ground make 1 or 2 flights to make sure it is going to run right before you try any aerobatics, keep enough altitude to get back to the runway dead stick just in case. |
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