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HomeRC & Power✈️Aircraft🚁HelicopterEngines Plugs Mufflers Fuel › YS61 ST 2 tuning issues.
12-10-2013 05:08 PM  5 years ago
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YS61 ST 2 tuning issues.
I purchased a used Raptor 60/90 with a YS61 engine that had not been ran for quite some time. So I disassembled the carb, boiled out the body, clean everything and inspected orings, replaced all fuel lines and cleaned and tested the one way valve. I have to correct lenght of hose cut from the backplate to the valve also. Running 30% cool power, I have installed a #8 plug as well. I will try and make this brief as possible. I start with the 3 needles set to factory specs. The engine starts and I can get it to hover trouble is, I cannot get away from either while coming off idle it falling on it's face and dying or then once I get it in the air it sputters and makes the tail twitch. I suspected at one point it may have been the regulator so I purchased a new one from YS for about $60 but once I installed it I got no fuel flow at all through it. The new one has a pin in the place of where the adjusting screw use to be. Bottom line is after screwing with it I have now ruined it and am back to the original one. I have adjusted it to where while I am cranking the engine fuel will just run out of the line feeding the carb but after cranking the fuel will stop. The little screw I have read about on the body that can fall out is missing but someone has filled the hole with epoxy, I am guessing this is acceptable just as long as there is no air leaks. Can you fella's please help me get this thing tuned, I have ran over a gallon of fuel through this thing and just can't get it right.
12-12-2013 01:12 AM  5 years ago

rrKey Veteran

Morgan Hill, CA. USA

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I run YS56SR and the YS91SR-3DS.
I do not know if your regulator is the same as mine.
I suspect the new regulator you bought was the same, but your "old one" sounds different. None of mine have ever had adjustments.

There is a screw on the side, but it should covered in goop.

The regulator is simple in concept.
Assuming the tank is pressurized, it should completely block (stop) fuel from flowing into the barrel of the carb if the crankshaft is not spinning.
And, the crank needs to be spinning fast enough - like having a starter attached.
From your description, it sounds like your replacement was working as designed.
And, maybe your old one is working the way it is supposed to now also.

The YS motors run rich - it can be a bear to tune them.
My 91SR-3DS has to be "nursed" over the hump from idle to idle-up. Once it reaches idle-up, then it is better.

If you are truly starting with the factory needle settings, then you should start to lean out the hover & high-speed needles.

If it is as rich as you describe, I'd go 1 click of hover and 2 or 3 clicks of high-speed and see how it acts. Adjust both until you get a little more reliability.
But, don't go more than 3 or 4 clicks of hover and/or 10 clicks of high-speed. If you get that far, and things aren't improving, there is definitely something else going on.
12-13-2013 02:22 AM  5 years ago


Richmond, VA, USA

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A healthy STII is pretty brain dead easy to tune.
Set the idle for whatever idles well.
Set the hover needle to 1.75 to start and anticipate it ending up at about 1.5 to 1.25 open.
Start with the high speed at 1.25 open. It'll be pretty rich. It'll end up between 1.00 and 0.75 turns open.
REMEMBER: The hover needle affects the high speed needle, but not vice versa. Tune the hover needle first and then the high speed. DO NOT EVER make gross changes to the hover needle, especially in the leaner direction, without first richening the high prior to going in forward flight. It could go dead lean as the throttle goes fully open.

Reg issues aside, the most common causes of problems with tuning are a bad ring, bad rear bearing, and trash hiding in the fuel passages in the carb. If needle settings are much outside of the ranges I gave, don't waste your time fighting it. You have to isolate the underlying cause.

Ben Minor
Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA
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