| Tuning is simply adjusting your engine for peak | | | | Leaner: reduced smoke, sound starts changing to |
| performance. The factory-fresh settings may be a | | | | higher pitch |
| good starting point. However, you may need to | | | | Leaner still: little smoke, max rpm reached |
| compensate for higher altitudes, or for temperature | | | | Too lean: very little smoke, max rpm can be heard |
| changes with the seasons. Changes in fuel type or | | | | falling off. Open the needle valve up 20 or 30 degrees |
| engine wear, may also require a tune-up. | | | | from this point. If you have a tachometer, open the |
| Relatively more fuel to air is known as a "rich" mixture, | | | | needle about 300 rpm less than max. |
| while the opposite is known as a "lean" mixture. A lean | | | | 5) Still at high throttle, perform the pinch test. Briefly |
| mixture generates more power, but also generates | | | | pinch then release the fuel tube going into the carb. If |
| more heat. Too much heat could damage the engine. | | | | the engine momentarily speeds up, then slows back |
| A rich mixture generates less power and less heat. | | | | down, you're done. If the engine does not speed up, or |
| Too rich and the engine might quit while you're flying. | | | | quits, then it is too lean; richen the needle some more. |
| The popular twin-needle carburetor has two needle | | | | 6) Now throttle back to idle; let the engine idle for a |
| valves. The high speed needle controls the total fuel | | | | couple minutes. |
| flow into the engine, and affects the engine's behavior | | | | 7) Now perform another pinch test. This time pinch and |
| from half to full throttle. The low speed needle tends to | | | | hold the line. The engine will want to speed up and die. |
| have more of an effect from half throttle down to idle. | | | | If it speeds up immediately, it's too lean, richen the low |
| Both the low and high speed needles can be richened | | | | speed needle. It should take 4-6 seconds to speed up |
| (counterclockwise turning), or leaned (clockwise turning). | | | | and begin to die. Any longer and it's too rich. |
| Tuning Procedure: | | | | 8) Also check the throttle transition. With the aircraft |
| 1) Start with the factory recommended needle valve | | | | secured and engine idling for a couple minutes, |
| settings. | | | | advance the throttle quickly to fully open. If the engine |
| 2) Start the engine. | | | | hesitates, the low speed mixture is too rich. |
| 3) With the engine or aircraft secured, open the throttle | | | | For more information about Model Airplane Engines, |
| to full. | | | | visit the RC Airplane Advisor — Model Airplane |
| 4) Lean the high speed needle slowly and watch and | | | | Engines. |
| listen: | | | | This article may be reprinted if proper credit is given |
| Too rich: lots of smoke, low pitched sound | | | | and all links left intact. |