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YS140L gets rough at idle

Old 07-22-2007, 08:23 PM
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Default YS140L gets rough at idle


My YS140L runs rough when at idle for very long. The idle at startup is fantastic and even and just fantastic.
The flight is great for a while, then about 5 minutes into the flight it begins to run a bit rough and especially at idle. It is on an OLD Funtana and I just do rolling circles, flat spins, and some hovering (but it scares me when it begins to get rough).
I came in to adjust the needle maybe and it won't slow down much at idle, then eventually comes on down and is rough and will die. I started it again and it idles rough, but then comes back up to power and no problem.

The system stays pressurized the flight and holds very well. Not sure what is up with it. I changed plugs and no change. The fuel is also good as I flew a Saito with it and a YS 120 both yesterday.

Here is a question though.. this engine has a low end adjustment. I never messed with it until today. I think it was completely closed down. I opened it a bit and it ran rough as heck and messed with it a little but eventually closed it back down and it ran well... of course until I was at mid-low range and idle.

Here is some additional information... I bought it used and sent it in for a check up about 4 months ago and had bearings replaced, gaskets, etc and it ran great there they said.
I fly 20% Byron's fuel. I do live in Phoenix and it gets hot... maybe I burned a plug? I changed the plug and it didn't seem to matter.
I set the high speed needle to where it just screems with my 17x6 prop on it and then richen it up until I can hear the rpms drop a bit...just to make sure I don't burn it up.

Any advice on where to set the low end needle valve? Altitude here is 1000ft and temp was about 90F in the am hours....I am long gone by the time it gets to 112F.

I am a bit scared to fly my planes with it running so unpredictable.
I am lost at where to start.

Side note: My YS120 is the best engine I have ever owned. I NEVER mess with the needle even as the seasons change.

Old 07-25-2007, 10:31 PM
Troy Newman
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Default RE: YS140L gets rough at idle

The idle is likely too rich...this is a sign of a rough idle....

I live in Phoenix area too...actually Goodyear and if you have trouble maybe we can meet up and I'll take a look at it. I just got back from a long trip flying and might not be going out for a few days...but we can meet up sometime.

Just send me a PM or email and we can get together.

Since we are close this is one I can actually put my hands on and help fix.

I don't know about your fuel of choice. I have not seen good experiences with that fuel. Some folks may like it but I would bet there are not many running YS engine that use Byron's. Make sure you filter your fuel really well. I have seen some experience some problems with crap in the regulators from that fuel.

Troy Newman
Team YS
Old 07-25-2007, 11:02 PM
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Default RE: YS140L gets rough at idle

Hi Troy,

That sounds like a great plan. This is my second YS engine, and I am hooked. My 120 is unshakable so I know this 140 can join that club as well.
I do have some 30% Cool Power Heli I can use.

I just sent you an email.

Thanks a ton,

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