Starting a New Engine for the First Time

The starting method outlined below uses an electric starter. There are other hand starting methods that work, but I prefer to use an electric starter. For the 150 and 180 engines it is best to use a strong starter like the Sullivan Dynatron model; this starter works well with a 12 volt battery but can also handle up to 24 volts.

On your engine carb first set the main high-speed needle valve 4 turns out. Check the low-speed needle position; it should be about level, or 0.5 mm below the level, of its housing. New engines will have this set in an appropriate position and it is best to leave it as it comes from the factory for the first start. If you need to reset it, turn it so that it the screw is flush with its housing and then turn it in about one half turn. The low speed position of the throttle should be set by first setting the transmitter throttle trim at neutral then mechanically adjusting the linkage so that the low-speed throttle opening is about 1mm and you can check this by peering down the carb throat (perhaps with the aid of a flash-light). The high speed  throttle position should be set so that full throttle stick completely opens the carb.

Don’t try to start the engine with the throttle wide open (dangerous) or completely closed (it won’t start). You must look down the carb intake and set the throttle starting position such that the carb is open just a little as was mentioned above; about 1mm is OK, or up to about 1/4 throttle. It is convenient to arrange the mechanical linkage to the throttle such that the throttle stick is full back and throttle trim is centered for this starting position.

Next get the fuel up to the carb by fully opening the throttle and turning over the engine by hand with your finger over the exhaust outlet. As soon as the fuel gets to the carb continue turning over the engine about three turns to get some fuel into the engine. Another way to do this is to set full throttle position and to spin over the engine with an electric starter; it is not normally necessary to put your finger over the exhaustwith this latter method.

It is important to get some fuel into the engine but not too much. Next turn engine over by hand 3 or 4 times, you might see some fuel drip out the exhaust (assuming the exhaust points downward, as it should).

Next set the low throttle position like was mentioned above. Connect up the glow plug battery and then use an electric starter. It should start. If it backfires it may loosen the prop nut or even throw off the prop and this is a sign that you had too little fuel in the engine and you need to re-prime it. If it does not back-fire and yet still does not start it probably means you have no fuel in the engine or the fuel line is empty (assuming the glowplug and battery are OK).

After the engine starts leave the glowplug battery connected and let it run at low speed (about 4000 rpm maximum) for the entire tank of fuel. You could try removing the glow-plug battery and it may run without it even at a rich mixture setting.  You may have to leave the glo-plug battery on to keep it running. Don’t try fiddling with the needles yet and run the engine for at least 10 minutes (preferably about 15-20 minutes) total at this low speed and somewhat rich mixture.

Next start the engine again and slowly advance the throttle to maximum. There should be lots of smoke as the mixture will be quite rich. When it gets to maximum throttle remove the glo-plug battery. Use a tachometer to measure the rpm and slowly lean the mixture (turn main high-speed needle in) until you get peak rpm, then richen the mixture (turn needle out) until the rpm drops about 200 rpm below its maximum value. If the engine is unduly rich you may have to leave the glow plug battery connected at first to stop the engine quitting. You really should have a tachometer because it is quite difficult to discern maximum rpm by ear.

The following text that describes low-speed needle adjustment applies to all Saito single cylinder engines except the Saito-30 that has an air-bleed type carb. For an air-bleed type carb the procedure is the same except turning the screw in will richen the mixture.

Next lower the throttle on your transmitter stick all the way back and adjust the throttle trim so that the rpm is about 2200--2400 rpm or whatever you think is a reliable lowest speed; do not try for a very low idle rpm until you have more time on the engine.. You should next adjust the low-speed needle, and you want the leanest possible low-speed needle setting without the engine quitting when you rapidly advance the throttle from its lowest position to half-throttle or full throttle. You will notice that with the main throttle stick all the way back, if you lean the low-speed needle the rpm will increase, therefore after you make an adjustment of the low-speed needle you should re-adjust the throttle trim for about 2200--2300 rpm. or whatever you think is the lowest reliable idle speed.

Assuming the low-speed needle was initially first in a rich seeting, turn it in about 1/8 turn, reset transmitter trim for 2200-2300 rpm, and then rapidly advance the throttle from lowest position to about 1/2 throttle. If the engine does not quit, repeat the procedure, until the engine quits , then turn it out 1/8 turn at a time, readjusting throttle trim, until you have the leanest mixture without the engine quitting when you rapidly advance the throttle.

Now go back to re-check the main needle setting by fully advancing the throttle and adjusting for about 200 rpm lower than maximum as you did at the beginning. The engine should now be reliable enough to fly without the engine quitting. After about an hour of subsequent flying time you should readjust the mixure settings again at which time you could try for a lower idle rpm if you want. I am able to get reliable low speed rpms of about 1800 after the engine is well broken in.

Remember: The objective is to get the leanest possible setting on the low-speed needle such that the engine does not quit when the throttle is quickly advanced from idle to 1/2 throttle, and also from idle to full throttle. The high speed needle should always be a little rich.  Please see the “Throttle Setup” page on this web site for more information on setting up the carb.

After the engine is fully broken in (about 2 hours total) and the mixtures are set it should not be necessary to fiddle with the mixtute settings. I have engines that have been flying for 3-4 years where I have not adjusted the mixtures.

It is often quite difficult for beginners to know when they have the correct mixture with 4-stroke engines because the rpm changes little as the the needle is turned. Don’t judge the mixture by smoke from the exhaust. Set the idle mixture so that the idle is reliable, then set the high-speed needle a little rich. If the engine runs OK that’s fine, don’t worry about the amount of exhaust smoke. Never adjust the low-speed mixture needle to set the idle rpm - the low speed needle sets the fuel-air mixture for reliable operation and the transmitter trim should be used to set the lowest speed idle rpm (initially for a new engine set this to about 2200-2300rpm.

Idle Mixture Too Rich  Symptom: Engine idles OK for a while, say 30-40 seconds, then just quits. Also, engine hesitates and does not accelerate quickly from idle when you advance throttle. Solution - lean low-speed needle 1/8 turn and try again.

Idle Mixture Too Lean Symptom: Engine will idle fine for extended period, but quits when throttle is rapidly advanced frrom idle. Solution - richen low-speed needle 1/8 turn and try again

Starting an Engine That is Broken in With Correct Mixture Settings

Fill tank then prime engine by opening throttle and spinning engine with electric starter. Set low throttle. Connect up glow plug battery, Use electric starter to start the engine, Remove glow-plug battery. Wait about a minute for the engine to warm up before trying full throttle.

Another method that some find easy is to not prime the engine, but to fully close the throttle (either with low throttle trim or the transmitter engine ‘kill switch’). Next with glow-plug connected spin the engine over with an electric starter, then with engine spinning a helper holding the transmitter advances the throtttle trim (or releases the kill switch). The engine then should start as it draws fuel. This method may be particularly helpful if you are trying to start a larger engine (150 or 180) with a small electric starter that has insufficient power to turn over a large engine full of fuel.


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