I have a problem with an OS 32 ABC engine with 20c carburettor.

I have installed the engine in a Shuttle ZXX with the standard construction and muffler with a Futaba 240 gyro and fibreglass blades.

I have run the engine in as per the recommendations and I cannot seem to get the motor to perform efficiently.

My fuel mixture is 5% nitro, 5% castor oil, 15% synthetic, and 75% methanol.

I have the model vibrating from the RPM and I have not been able to eliminate it only reduce it.
I have had the motor attempt to stall on me mid flight.
I have excessive amounts of oil exiting from the exhaust.

The motor in idol position will stall on me as I apply power for take off and as I walk the model out to the flight line. The motor in idol speed sounds like a four stroke motor and as I turn in the low end needle setting this four stroking is reduced. I have also noticed that as I do this the vibration in the rear tail is reduced.

In frustration of not being able to get the motor running I removed the carburettor and reset the it back to factory setting as per the instruction manual and the main needle valve to 2 ½ turns out from the fully closed position and started from the beginning again. I am able to confirm the carburettor factory setting to be 2 2/3 turns in from the fully opened position for the low end needle valve for this motor.

I commenced to fine turn the motor and found the settings too rich and the model was struggling to lift off. After much time of adjustments I managed to achieve a satisfactory setting to enable the model to fly with suitable recovery and flight settings, but still needing fine tuning. Landing the model from a hover and with the throttle at zero and the trim setting at 75% the motor takes some time to return to a low idol RPM.

To achieve these settings I had to lean (turn in) the low end needle valve approximately ¼ of a turn from the factory setting and lean (turn in) the main needle valve to a final setting of 1 1/6 turns out from the fully closed position. With these setting the motor still wants to stall in the stationary position and I have excessive amounts of smoke and oil coming from the exhaust. The model requires further fine tuning to reach the optimum flight settings. I feel the low end needle valve needs to be leaned (turned in) an additional 5mm of a turn and the main needle valve an additional 5 clicks approximately. During flight I have excessive amounts of oil and smoke exiting the exhaust system. I touched the motor after flight to check how hot the motor was and found it to be not any hotter than the other motors at the field ie I feel it was not over heating.

How do I stop the motor from stalling on me while carrying it out to the flight line ??
How do I stop the motor from wanting to stall on me during flight ??
What do I do to get the motor working correctly?

Chris

There is more to tuning the engine then I can tell you over the net. I will try to help in getting it setup.

What glow plug are you using? Have you tryed an Enya#3. The O.S. like more nitro, atleast mine do. I am runnig 25% right now. IT will fly on 15% but the power is down.

My main needle is right at 1 1/2 tunrs out. I set the low end needle by attaching a "CLEAN/ NEW" piece of fuel tubing to the carb and blowing through the tube while turning the low speed needle out just until I could hear the air flowing out of the carb.

Then there is the matter of your pitch and throttle curves. Tese will effect how the engine responds to the load of the blades.

Hope this helps a little.

Dru.

Vibrating is usually from something being imballanced... Shaking the whole heli is rarely from the engine.
Your main rotor and tail rotor should be checked for ballance.
Also check blade tracking on both the main and tail rotors. (yep you can tweak the tail rotor tracking.) If they aren't tracking right, they can induce an oscillation simulating an imballanced blade set.
Its easier to set the main track than the tail... paint the tip of one tail blade with a magic marker (won't un-ballance the rotor... I hope you don't have black tail blades...) When the engne is turning the blades at high speed, low pitch and with the LG held firmly (keep on the ground, prevent pivoting), apply some rudder. Watch from directly behind for one tail-rotor blade to be consistently in a different track from the other. You only have 1/2 ball link turn resolution... so adjustment may never get them tracking exactly.

It is easier to tune a heli engine out of the heli, on a test stand using a prop. (especially a new engine.) The main rotor wants to get to turning (something about a centrifugal clutch... [img]i/expressions/face-icon-small-wink.gif[/img] ) and you can't safely get at the needle valve to tune the high end. If the high end is wrong, the low end will probably be wrong.
In the case of a dual needle carb... its possible to have the low end needle take control of the carb's high end, but that doesn't sound like what you have going on. If anything, your low end is probably on the rich side.

Tthe factory settings are approximations that should get the engine running... not the final settings where the engine should run properly. A tiny manufacturing difference in the needles can make a large difference in the needle setting needed. Also, the factory sort of expects 10% to 15% nitro (for most engines... 30% is expected for some heli engines.) and you use LESS fuel when using less nitro.

Use a 10X4, 9X5 or 9 X 6. (appropriate for the .32) Run 2 tanks of fuel through the engine. The main needle setting will probably need a major change in the middle of the first tank, and a smaller change somewhere durring the second. (assuming new engine...) The needle may need a TINY tweak difference when mounted in the heli.. richer due to higher operating temp. If you have to move the needle more than 1/4 turn from the final setting you get on the test stand... something's wrong. (write the setting down... you'll need it.)

When setting the main needle, you want to get max rpm, then open the needle 1/8 turn (about 2 to 3 "clicks" on conventional ratcheting needles.) The engine should put out a visible misty/foggy exhaust. (if you can't see the exhaust.. its too lean.)

The low end should be set for the lowest speed stable idle possible, then test for transition to high speed. If you move the stick at a rate that takes 2 sec to go from idel to full throttle, the engine shouldn't hesitate. (it may take 1 sec more to get to full speed... but it shouldn't sag as you move the throttle.)

A test stand is an invaluable tool for diagnosing the heli engines! If it works right on the stand... then its in the fuel tank setup when problems persist in the heli. A vibration (or tracking) problem can "foam" the fuel, making the engine get air bubbles. No engine will run properly if getting air bubbles in the fuel line.
It is also possible for there to be a pinhole in the fuel lines somewhere... even in the clunk line inside the tank. (that one can give you fits... dies for "no reason" at 1/2 tank every time for example, when the hole is near the stopper.)

As you can see... we can write LONG books on engine tuning. I haven't covered half of it yet!

Dru

I am running a OS#8 plug.
I like you method of determining the factory setting and will try this out.
I understand the pitch and throttle curves play a big part in the motor turning and have taken this into consideration by adjusting both curves to suite the model.
BUT
you will notice that there will be a point at which both the pitch and throttle curves will not make any difference to how the motor runs ie if the motor is to rich or lean. I feel this is where I am at, at this moment.

Chris E

I was not able to post last nite because of the very poor connection I have.

Here are a couple of things to try:

Try an Enya #3 plug. I did not have good luck with O.S plugs at all. Do not get hung up on how far in or out the needle's are. They will vary from engine to engine as well as area to area. The main needle on one of mine is open just over 1 turn out and the low speed needle is out 1 1/2. The other ones main needle is 1 1/2 and the low speed is also 1 1/2 turns out.

Try to get the engine high needle set first. Try to get it to hover, lots of smoke and no power try leaning it out a little. Keep turning the needle in until it is running well. I had to leave the nystarter atached to the glow plug to keep it from dieing at idle. Can you get some 15% heli fuel? When you adjust the main needle do it 1 or 2 clicks at a time. Turn the low speed needle as little as you can. I would turn it the thickness of the screw driver blade until mine was tuned.

Have you heard of the pinch test to set your idle??? Start your engine, with the glow plug battery still atached give the fuel line a pinch. Does the rpm stay the same, go up, go down? If it goes up as soon as you pinch it it is a little lean. If it stays the same it is running rich. If it goes down and wants to die then it is to lean. Now do this with out the battery attached. That should put it close to being right on the money.

I have to disagrre with Mr FHHuber. My Nexus would do the funckey chicken when the engine was not happy. It would kick the tail around 120 degrees and the whole heli would jump up and down about 6 to 10 inches.

You are getting two ideas from two people so between the three of us we should be able to get the engine tuned.

Let us know what works and what does not.

Dru.