| 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 |
| engine wear, may also require a tune-up. | | | | degrees from this point. If you have a tachometer, |
| Relatively more fuel to air is known as a "rich" | | | | open the needle about 300 rpm less than max. |
| mixture, while the opposite is known as a "lean" | | | | 5) Still at high throttle, perform the pinch test. Briefly |
| mixture. A lean mixture generates more power, but | | | | pinch then release the fuel tube going into the carb. |
| also generates more heat. Too much heat could | | | | If the engine momentarily speeds up, then slows |
| damage the engine. A rich mixture generates less | | | | back down, you're done. If the engine does not |
| power and less heat. Too rich and the engine might | | | | speed up, or quits, then it is too lean; richen the |
| quit while you're flying. | | | | 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 | | | | 7) Now perform another pinch test. This time pinch |
| behavior from half to full throttle. The low speed | | | | and hold the line. The engine will want to speed up |
| needle tends to have more of an effect from half | | | | and die. If it speeds up immediately, it's too lean, |
| throttle down to idle. Both the low and high speed | | | | richen the low speed needle. It should take 4-6 |
| needles can be richened (counterclockwise turning), | | | | seconds to speed up and begin to die. Any longer |
| or leaned (clockwise turning). | | | | 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 |
| 2) Start the engine. | | | | engine hesitates, the low speed mixture is too rich. |
| 3) With the engine or aircraft secured, open the | | | | For more information about Model Airplane Engines, |
| throttle to full. | | | | visit the RC Airplane Advisor - Model Airplane Engines. |
| 4) Lean the high speed needle slowly and watch and | | | | This article may be reprinted if proper credit is given |
| listen: | | | | and all links left intact. |
| Too rich: lots of smoke, low pitched sound | | | | |