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YS 91-AC idle

Old 11-17-2007, 04:38 PM
  #1  
skawbo_dk
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Default YS 91-AC idle

Hi,

I'm currently breaking in a YS 91-AC which sofar have had one gallon through it. The problem is the idle. With glow it idles ok at 2000 rpm, but when it is removed the rpm drops with 300-400 rpm and it is difficult to keep alive. When the engine is warm (when I manages to get it in the air) it is ok. I use an OS F plug and changing it with a new one does not help. Should I lean the low speed needle?

Br

JJK
Old 11-18-2007, 12:32 AM
  #2  
Troy Newman
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Default RE: YS 91-AC idle

At 2000rpm with glow idle is fine and remove glow it drops off rpms like this its too rich on the low end. Adjust the air bleed idle idle adjustment screw out for leaner (CCW). If you get to about 2.5 to 3 turns open on this idle screw and it is still to rich at idle....The you need to Lean the Regulator screw (IN or CW for this screw) and reset everything again.

This is a good way to tell if the setting is too rich on the low end...HOWEVER...you can't get accurate final settings with the glow driver connected. It will almost always overcome wrong mixture settings with the glow plug glowing good from the battery. See these engines rely on the heat generated to keep the glow plug alive and glowing properly from the last "combustion"

So if the engine is too rich the glow plug will burn colder and eventually the engine will load up and die. A battery connected will artificially keep good glow on it and your needle adjustments are in vain. I see all the time guys at my local club field running the engine up with the battery attached setting the mixture both top end and idle then...when they remove the glow and taxi out to takeoff it quits...Or it quits on Takeoff, or ?????

It amazes me....Go up and help the guy get it set properly....explain why you don't want the glow connected while setting the mixture and its runs great for the day.

next weekend he is out and doing it just like the he was last week...and the engine is a junker.

Oh Well you can't save everyone!

You are likely not too rich....its just a bit rich so you should be able to dial it in well. By the way in the first few gallons of the break end period...you need to realize these settings will drift a bit. This is normal until about 3-5 gallons...then it will get very stable.

Troy Newman
Team YS
Old 11-18-2007, 03:52 AM
  #3  
skawbo_dk
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Default RE: YS 91-AC idle

Hi Troy,

Thanks for the advice. I'll try to lean the low end so that I do not get a drop in rpm when glow is removed (keeping the 2.5-3 turns in mind).

Br

JJK
Old 11-18-2007, 03:01 PM
  #4  
skawbo_dk
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Default RE: YS 91-AC idle

Hi,

Just a follow up: Today I gradually leaned the low end to 3 turns out. This certainly improved things and now I can keep the engine running at idle for a sufficiently period before takeoff [8D]. The rpm now only decreases slightly when glow is removed. For now I will try to leave the settings as they are and then possibly adjust the regulator when the engine is fully broken in.

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