Starting Badly Out of Adjustment Engines
What to do with that used engine you just bought that feels like it has compression but won't run right. (maybe not at all) This assumes you don't have the mfgr's instruction book.
Check the glow plug and se if it functions. Replace if needed. The plug should glow a bright orange with 1.2 to 1.5 volts applied. It should not have the appearance of an ash buildup on the coil when cold. (Ash buildup indicates a failing plug, even if it will glow.)
Hopefully the engine will start at its current settings, and only minor tuning of the main needle and idle will be needed. The engine's high speed is adjusted properly when the main needle is opened about 2 clicks from where it will run at full throttle with the airplanes nose pointed straight up, however long you keep it pointed up. The low speed is adjusted properly when the engine will run smoothly and slow enough not to move the airplane forward, and will smoothly increase speed when the throttle is opened rapidly.
Basic starting a Badly out of adjustment engine: (assumes engine is mounted with servo control connected)
1) Find out where you are: carefully close the main needle counting revolutions and note to the nearest 1/8 revolution. Needle is closed when resistance to closing increases. Do not force it. Remove the needle and inspect for dirt on the needle or in the seat assembly. clean as needed. If dirt was found... set the needle exactly to original setting, ignoring #3 below.
2) If the engine has a needle valve idle adjustment close the throttle and measure as above, but note to the nearest 1/32 turn. Put it back where it was. If the engine has an air bleed idle adjust, simply close it, and open it 1 turn. (remember... I'm doing badly out of adjustment here)
3) Based on how far open the main needle was in #1: If it was under 1 turn it was too far in for any engine. Open to 2 1/2 turns. If it was between 1 and 2 turns open to 1 1/2 turns. If it was over 2 turns open to 3 1/2 turns.
4) Fill fuel tank and connect fuel line to engine. If available connect muffler pressure to fuel tank vent. Place finger over carb and rotate prop until you see fuel (fuel lines are normally transparent) entering the carb + 1 rotation.
5) Set carb fully open. Connect glow plug power source. Using care to avoid being cut by the prop, pull prop backwards into compression and allow it to pop forward when it kicks. Engine should start, and might keep running, so pull your hand clear as you let the prop kick forward.
If the engine runs briefly at high rpm... open the needle 1/4 turn and retry. If it runs and spits fuel... close the needle 1/4 turn and retry. If it trys to run backwards do not adjust the needle and retry.
If you find yourself going back and forth in the above... go halfway. ;) When the engine will run continuously, slowly adjust the needle seeking the highest RPM. Open the needle appx 1/4 turn from max RPM.
The engine should be at an acceptable setting for high speed.
6) Setting low speed: Some carbs are VERY touchy about the low speed needle setting. If the carb has a black body with a brass wheel on the side that has a small slot... it is a Perry carb and the slot needs to be very near
centered between the little index marks near the main air opening. The engine will not run more than 1/8 turn from there.
Needle valve type idle adjust is very similar to high speed adjusting... the rpm you are after is the slowest stable speed where it is not spitting a lot of waste fuel out.
Idle air bleed adjust types you are adjusting for a smooth reliable idle setting with a small opening of the main carb barrel.
Generally adjusting the needle type will need to be less than 1/8 turn from where it was originally. This will be 1/2 turn to 3 turns from being seated when the throttle is barely cracked open.
The air bleed type may need anywhere from 1/2 turn open to 3 1/2 turns open for a good smooth low speed idle. The engine should stop quickly when the main throttle opening is fully closed.
Idle tuning takes practice and the sound has a lot to do with what adjustments are to be made... High speed adjust has to be correct or the idle adjust is meaningless. Idle can be very bad with the adjustment out by less than 1/32 turn.Source : n/a
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