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YS 1.40L sensitive needle

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Old 10-07-2011, 07:21 AM
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mlr53
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Default YS 1.40L sensitive needle

I have a YS 1.40L that was sent for a through refurbishment due to sitting on the shelf for over a year. They changed the plunger and spring in the regulator, and instaslled a new piston ring, then test ran the engine. I installed it in a patriot with a new crank tank, and new fuel tubing. The plumbing is connected properly and the check valve is testing good (it holds pressure, no leaks). The engine gave me trouble and I replaced the diaphram in the pump, the old one seeming stiff. I managed to get the engine running and flew it a few times, but the needle valve is so sensitive it goes from blubbering rich to over lean and sagging in 2 clicks of the needle valve. The regulator was set at flush with the housing to start. I tried to lower the regulator pressure setting 1/4 turn but needle sensitivity is still the same. I am running 30% nitro, 20% oil helicopter fuel.

Anyone run into this issue? Any suggestion to correct the problem?
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Old 10-07-2011, 07:30 AM
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Default RE: YS 1.40L sensitive needle

What prop? What plug?
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Old 10-07-2011, 08:23 AM
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Default RE: YS 1.40L sensitive needle

APC prop 16.5 narrow x 10 turned down to 16x10 N
YS plug
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Old 10-07-2011, 08:27 AM
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Default RE: YS 1.40L sensitive needle

Prop doesn't seem to make a difference, I have tried other sizes of APC props and still had the same problem.
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Old 10-07-2011, 09:25 AM
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Default RE: YS 1.40L sensitive needle

Check the actual needle valve. Unscrew it and look at it, if it has had a long extension on it it will wear with a step in it that will exhibit exactly what you describe if your elevation requires setting the needle where the step happens to be. If it is not worn while you have it out flush out the seat with raw fuel in the event you have some gunk creating a blockage.
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Old 10-10-2011, 05:34 PM
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Default RE: YS 1.40L sensitive needle

Check it, the needle does not have a groove or notch and feels smooth using a finger nail to feel for a worn notch. I have also pulled the needle seat and checked for trash or restrictions but found none.

 Would reducing the regulator pressure make the needle less sensitive and what other effects would that have on the engine?
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Old 10-11-2011, 07:22 AM
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Default RE: YS 1.40L sensitive needle

You can't lower the pressure, you can only lean and richen the regulator. Out will richen by allowing the plunger to come off it's seat further thus allowing a larger volume of fuel to pass.

When you had the needle and seat out did you flush raw fuel from the regulator through the needle and seat?
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Old 10-13-2011, 10:19 AM
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Default RE: YS 1.40L sensitive needle

Yes, it all came out clean, no trash.
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Old 10-16-2011, 05:37 AM
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Default RE: YS 1.40L sensitive needle

If the needle is good and there is no trash in the seat, let's get back to basics. The check valve is a YS unit and it is working properly? Can you swap it for a different one? Try a different YS#4 or OS#F plug. Changing out the diaphragm should not cause issues like this. You mention having issues with the engine that made you change the diaphragm what was the issue?
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Old 12-12-2011, 04:05 PM
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Default RE: YS 1.40L sensitive needle



Had the engine torn down and reassembled, found a leak on a fuel tubing fitting on th eback of the engine. Reassembled and it ran great on the bench. Put it back in the model and 2 flights later it ran lean and RPM sagged. Pulled it out and put back on the bench, it ran perfect. upon installing back in the plane I pulled the fuel filter out and it ran great. The filter was a crap trap and does not appear to be plugged nor did any trash come out of it. My engine guru informed me that they have similiar issues on other YS engines with a crap trap and seem to think it restricts the fuel flow causing the engine to run lean. It's sure is runniing great now.

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Old 12-14-2011, 06:27 AM
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Default RE: YS 1.40L sensitive needle

I would think the crap trap worked if it took two flights to go lean. I personally use a different filter but now I need to go get a crap trap to test. Thanks for the info. Glad you got it running again.
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Old 04-19-2012, 10:04 AM
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Default RE: YS 1.40L sensitive needle

Petec, have you gotten a crap-trap to try on a YS 140L? If so what was the result? I have this engine and have recently put it in a pattern plane. I just put the engine back into service after many years on the shelf and I am using the crap-trap fuel filter. So far my only issue is poor idle. When I throttle back to 2000 RPM it stays there for about 10 seconds and then gets slower and slower until it dies. I cannot see any debris in the filter.
Thanks for any feedback.
Bob
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Old 04-24-2012, 11:19 AM
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Default RE: YS 1.40L sensitive needle

I have not gotten around to that, unfortunately time is at a premium for me. I have always used the Dubro machined aluminum filters with good results.

If your idle is going down until it dies that indicates a rich condition on the bottom end. If the transition is good, without stumbling, you might want to back the low speed needle out a bit at a time to open the air bleed and lean the idle.
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