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| Version | User | Scope of changes |
|---|---|---|
| Dec 12 2006, 8:44 AM EST (current) | venkatarun | 614 words added |
| Dec 11 2006, 1:56 AM EST | venkatarun |
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Hi
•Tuning the engine, or setting the mixture, is a very important part of helping your engine have a long and trouble free life. There are some terms you will come across that can be somewhat confusing. For instance, you have a 2 stroke Engine but you are told to run it at a four stroke. Sounds silly? Well this is just a term that is used to indicate how rich to set the mixture. All will be explained!
•Start the engine with the throttle fully open (if you have a control line engine then this doesn't apply because they don't have a throttle) and listen to the sound. This does take a little practise to understand the different sounds it will make. If the mixture is nice and rich (too much fuel being allowed in) then it won't rev very fast, the exhaust will have lots of smoke and will sound somewhat rough. Just to make sure it is running rich, open the needle valve a little more and the revs should drop a bit. If they drop and the engine still sounds rough then it is now running at what we call a rich four stroke, so-called because it sounds like it is only firing every second time the propellor goes around.
•Now slowly start winding the needle in (towards the closed position). What you are doing is making the hole that the fuel comes out of in the carby smaller so restricting the rate that fuel will be drawn into the engine. This is known as leaning out the mixture. Do it slowly because some engines have very sensitive needles and a small adjustment can make a big difference to the mixture. You'll soon notice that the revs start to rise but the engine still sounds rough. Eventually, as you continue winding the needle in, you'll hear a new sound starting to come from the exhaust.
•This sound is a much cleaner and higher pitched sound than it had before. At this point, leave the needle valve where it is and just listen. What you should now be hearing is the engine changing from the rich "four stroke" sound to the clean "two stroke" and then back to the "four stroke". Adjusting the mixture to a little leaner (turning in) will make it run most of the time in a two stroke and just occasionally making the "four stroke" sound. A little leaner still and the "four stroke " sound will disappear. The engine is now running at a rich two stroke. It still won't be at maximum revs but it will sound smooth.
•Now don't do the following unless your engine has been run in properly or it can be damaged. Very slowly lean out the mixture and listen to the sound. You will easily be able to hear the engine starting to pick up speed more and more as the mixture gets leaner. At some point you will notice that, even though you are still winding the needle in, the revs aren't getting higher or are even starting to drop. The engine is now starting to run lean and this is bad. The temperature of the engine will rise very quickly to the point where nasty things can happen to the piston or liner.
•When you reach the point where the revs are at a maximum (without going too lean) you should then wind the needle slowly out about 2-3 clicks until you can hear the revs start to decrease. This is the leanest mixture you should allow the engine to run at when you fly because it will lean out slightly more when in the air.
