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YS 91 St

Old 07-01-2008, 06:49 AM
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gau2857
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Default YS 91 St

I am looking for some help on setting the needle valves on a ys 91 st engine that i put in my helicopter. I have become frustrated with it and it is probably because i have never delt with the 3 settings for the needle valves. The only setting that seems to be right is the idle at about 2.5 and that is out of the range called out on the manual. The hover and high throttle needle valve settings i do not even think i can get close. I have spent hours trying to figure this out and have had no luck even with reading the forums. It seems like the helicopter has no power after 1/4 to 1/3 throttle. Sunday I spent another day trying to get it running and went through about 6 more number 8 glow plugs and the bolts that hold the head on the motor actuall fell out which i have never had heppen before. I am looking for help because I have been messing with the motor for the whole season and would like to get it straightened out.
Old 07-01-2008, 07:23 AM
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mjfrederick
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Default RE: YS 91 St

I don't have any experience with the helicopter engines, but if the head bolts came out, you may have been running the engine too lean and it overheated. If nobody else responds with any solid responses, you may want to contact Richard at YS Parts and Service.
Old 07-01-2008, 07:42 AM
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petec
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Default RE: YS 91 St

A couple questions. You say your idle needle is 2.5 turns out but not where the others are set so can you tell me where they are? WHat is the transition from idle to hover like? What is the smoke like?

Also, what is causing you to go through glow plugs? Are they becoming carbon fouled?

Getting my heli dialed in was a little more difficult than an airplane but you just need to make changes in one RPM range before moving on or you'll be chasing your tail....
Old 07-01-2008, 02:17 PM
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gau2857
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Default RE: YS 91 St

Ok well i went bac out to the field again and here is what i did. The manual says to set the idle to .5-.75 the hover to 1.5-1.75 and the high to .75-1.25. I set all of the settings to the rich side and started over with the head bolts in and tight. Then i noticed that it looked like there were little air bubbles comming from the pump to the carb. I change that short fuel line and it seemed to help but did not get ride of all the bubbles.

The glow plugs that i was going through the wire was seperated.
I do not know where other people's idle settings are i was just going off themanual.

I did not burn up any glow plugs this time out.
It seemeed like the transition from idle to hover was good, I had good smoke then when i went higher i lost the smoke. I thought i was getting some where and i needed to adjust the high setting. When i brought the throttle down slowly the enging would quit at about 1/4 throttle. Then i had problems getting it to idle where i could step away from it with it idling. So i had to start all over (chasing my tail!).
Anyway's i had it idling but not very good at @5/8.
I am thinking that maybe the air that i can still see in line going from the pump to the motor is the problem.
Anyway's that is where i am at now.



Old 07-01-2008, 03:11 PM
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petec
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Default RE: YS 91 St

Ok. Good info.

If you were burning out plugs before that is usually from running lean. You might want to richen your idle up to 1 turn to 1.25 turns as the manual suggests as a starting point and then you can always lean it. When the engine warms up it will tolerate a slighly rich mixture better then when it is cold.

If the engine is getting HOT it will not needle properly and you will wind up getting frustrated. Just concentrate on getting the idle and hover set and set them a wee bit rich. then once you get them stable move on the high speed needle.

Also, the bubbles in the short hose to the throttle body from the regulator would only concern me if the tank was not holding pressure.
Old 07-01-2008, 03:34 PM
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gau2857
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Default RE: YS 91 St

Back at it again!

Well I probably shouldn't say this because it makes me sound really stupid. What was wrong with the engine is that the fuel lines were not hooked up properly.

I had the fuel line comming from the muffler to pressurize the tank and then the tank going to the pump. In the directions!!!!!! is specifically shows you how to hook these up properly and that is going from the back of the motor to through the check valve and then to the tank to pressurize the system.

I guess it would have sounded better telling everyine that the pump was sucking air or something.

I still have to dial in the motor so if anyone has a good system of doing that I am open to learn. If not thanks for the help!
Old 07-01-2008, 03:43 PM
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petec
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Default RE: YS 91 St

Yeah, hooking the lines up properly is a big help. That and putting the check valve in the right way.

I wish I had a really easy way to set up a heli but I don't. It was idle to hove and then hover to FFF and checking the head speed and smoke to make sure I didn't get too lean..

If you find an easier way I am all ears.
Old 07-01-2008, 04:01 PM
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Default RE: YS 91 St

So in the end... it was a lean run... :-)
Old 07-02-2008, 12:37 AM
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Default RE: YS 91 St

Hi, I can see little bubbles in the line between pump and carb on my 91ST as well, it is not an issue. My motor runs a tad rich right across the range and is and should be cool enough for you to touch it for at least 15sec's (on the crank back-plate). Lots of smoke and even gurgles a little every now and then. It is important that you replace the glow plug after every 5litres (1 Gallon?) of fuel. I have also found that good quality fuel makes a huge difference, I run it on Xfuel 15% and have no hassles (alt=5500ft). Good luck!

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