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YS 120 not running right after rebuild

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Old 04-17-2009, 01:59 PM
  #1  
dditch
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Default YS 120 not running right after rebuild

Fellas,
Having a problem getting the engine to run past 1/3-1/2 throttle. It just dies.

I'm posting here in this forum 'cause I know lots of Pattern flyers use (or at least used to) fly the YS 120.
I got this engine back in 1995 cause it was the same engine I had in my pattern plane.
The engine has been mothballed since 1999 and I took it out and rebuilt it w/ the help of a friend.
The friend helped me pull the crankshaft and bearings out and I put new bearings, o-rings and gaskets in.
I cleane up the valves and set the spacing.
I also set the timing of the cam by lining the mark on the drive washer to the body and the dimple of the cam upwards.
Here is the central hobbies exploded parts diagram I am referencing:
[link=http://www.centralhobbies.com/Engines/parts/YS120NCEX.html]YS 120 NC exploded parts diagram[/link]

When first starting it up, fuel was leaking out of the regulator. Pulled it apart and I think the diaphram was not seated in right so I turned the regulator screw out about 5 turns from where it was so the diaphram would sit in there when putting it back in. Turned the regulator screw back in 5 turns. I took pics of how I placed the diaphram when installing (gasket goes on case side, clear diaphram goes on regulator side in the recess).
My initial problem was that fuel was not comming into the carb. I had to turn the regulator screw out a couple turns, then all the sudden, fuel would move. It started to move out of the regulator to the carb as I backe out the regulator screw 2-3 turns from it's original position.
Then it started up and would sound GREAT at about 1/4 throttle. It was not really holding an idle and ANY time we went past 1/3-1/2 throttle, it died.
We tried 1 1/2, 2, 2 1/2 and 3 turns out. I sort of recall I ran it at about 1 1/2 turns out, (not really sure). Anything past 3 turns and I can see the O ring on the needle valve Needle socket.

My tank is holding pressure. After letting it sit even 10 minutes at the end, when I accidently unplugged the clunk side of the refueling tube, fuel spewed out to let me know it was holding pressure. I think I have all the fuel lines all hooked up right (see photos).

I took pics showing the order that I place the gaskets as well as the plumbing of the fuel lines.

One thing I'm not clear on by the exploded parts diagram on the central hobbies website. # 73 the Regulator Balast. I don't see that on my engine.
Either my buddy took it off and lost it, It was removed and lost back in 1998 the first time it was reworked or it never had it.

I did nothing to clear out the tubes that go through the regulator body #46 and I'm wonding if I should pull that apart and maybe clean any gunk I find on it. Should I take that apart and then blow compressed air though the holse to clear it out or soak it in something?

I also need some sort of default or adjustment procedure for the #47 regulator adjusting screw. I've never had to touch it before. Both the initial use of the engine from 1995-1998 and after the first rebuild, I never touched that screw and the engine ran flawlessly.

I ran it today with 15% nitro 20% castor-synthetic blend Byron fuel.
If any other info or pics will help, let me know.
thx for any help

-David

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Old 04-17-2009, 02:22 PM
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Default RE: YS 120 not running right after rebuild

Additional information. The photo that shows the plumbing of the lines to the tank, the line that has the aluminum check valve on it goes to the top of the tank. The other line is going to the clunk. I'm wondering if that is even hooked up to the right nipples on the engine?
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Old 04-17-2009, 03:39 PM
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Default RE: YS 120 not running right after rebuild

Dave

Sent you a pmail
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Old 04-17-2009, 06:49 PM
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Default RE: YS 120 not running right after rebuild

dditch,

Yes, the hoses are correctly installed, and the engine is quiting due to lack of fuel, it is highly possible you have the engine internal fuel passages clogged, you will have to disassemble the engine completely and flush it, use alcohol, for extreme gum I use paint thinner (the paint thinner will dissolve the gum and all parts made of silicon like the regulator diaphragm so be carefull), and then try to blow all passages with compressed air.

After all that is done, you need to change all the seals, you show only the diaphragm side of the regulator, but the poppet valve (plunger) might be stuck or worn on the adjuster screw side, you need to take this apart also to clean it, get a new diaphragm, it looks in your picture like it is dented or marked on one edge, and if it leaked fuel I assume is because of this, the plunger and diaphragm are cheap so get new ones it might save you a lot of time, also, you need to change the O rings on the rocker arm push rods tubes.

The regulator should be flush with the housing after you reassemble the engine, do you have the engine manual? if not I'll email it to you.

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Old 04-18-2009, 03:28 PM
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Default RE: YS 120 not running right after rebuild

I started it up this morning after finding that the regulator housing was on backwards (tab was to the rear). I re-assmbled it with the regulator on correctly (tab towards prop). Started it up and same thing. I looked closer and there is air bubbles comming from the regulator to the carb. The silicone tubes were changed everywhere except to the tank where I took 1/4" off the tubes and pressure tested them. I see NO air comming into the regulator, just out from the regulator to the carb. I'll take apart the regulator again to see what is going on.
The gasket, diaphram and the O-Rin in the regulator were all replaced. I did a complete gasket and O-ring replacement on the engine when I did the bearings.
Something is letting air get in.
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Old 04-18-2009, 03:49 PM
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Default RE: YS 120 not running right after rebuild

Hmm, just finished taking it back apart, now I see what you meant about the diaphram. That was a new diaphram but since I originally installed it incorrectly, it left a crease on it where it was being pinched. In a semicircle but a pretty big dent on the ends of the creases. The design leaves no room for error the way that the diaphram seal is on the edge and if the seal is not good, air comes in from the outside. I like how my Walbro carb is on my Gas engine. The diaphram IS the gasket. Much easier to install.

I'll have to buy a new one (or two) and try again. I hope that's it.
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Old 04-19-2009, 04:54 AM
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Default RE: YS 120 not running right after rebuild

dditch,

Make sure you have the timing set proper on the engine. Look in the back plate of the engine and you will see the dot on the crank by the bearing journel. Line that up with the center seem of the engine then look at the cam gear and make sure the dot on the cam is to the top. Make sure the engine and gaskets are all back together right and then reset all needles. The high end needle should be 2 turns out and the low in needle should be 1.5 turns out from closed. The regulator screw should be flush with the regulator housing. Start the engine and let it warm up before going to full throttle. Once you get to full throttle adjust the top end to peak RPM and then back it off to a slite rich setting. Once the high end is adjusted start lowering the throttle to an idle till you get to around 2000 RPM. Let the engine sit there and listen and if the engine speeds up at idle then screw in the idle about a 1/4 turn at a time till you get the idle to hold. If the engine gets to 2000 RPMs and then starts to slow and want to quit running the turn the idle screw counterclockwise to lean it some and about a 1/4 turn at the time till it's right. Each time you make an adjustment go to full throttle and then back down. If you go to full throttle and the engine sounds like it's straining or if you know what predetination sound like you need to richen the regulator by turning it out. That gives it more fuel and if it's spitting and sputtering going up to full throttle then screw the reg. screw in to lean. Once you have the engine where it will idle ok and also transition good then you can go back to the idle and fine tune it some more. I hope this helps and once this thing is set you can forget it. Remeber the regulator screw controls the transition, in for lean and out for rich.

Larry
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Old 04-19-2009, 07:11 AM
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Default RE: YS 120 not running right after rebuild

I set the cam timing based on the notch on the prop washer(drive washer) and the dot on the cam already. That's what it said to do in a manual I downloaded.
This model does not have a low end needle.

Thx for the explanation of the regulator screw.

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Old 04-19-2009, 07:56 AM
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Default RE: YS 120 not running right after rebuild

I that engine the old "AC" type with the big expansion box on the back side of the head? Never mind I saw the photo at the top.

Larry
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Old 04-19-2009, 12:43 PM
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Default RE: YS 120 not running right after rebuild

One thing I'm not clear on by the exploded parts diagram on the central hobbies website. # 73 the Regulator Balast. I don't see that on my engine.
Either my buddy took it off and lost it, It was removed and lost back in 1998 the first time it was reworked or it never had it.
David,

This won't help you getting the engine to run but as I recall the ballast was added to later models to make the engine run the same inverted as upright. I don't believe it is a critical part.

Allan
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Old 04-19-2009, 08:50 PM
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Default RE: YS 120 not running right after rebuild

dditch,

The regulator also works as an idle screw in your engine model, so you have to adjust it so acceleration is good, it can smoke but it has to be smooth, if you need to make changes to the pressure regulator for idle adjustment then remember to go to full power to reset the engine pressures before checking the results.

Even if your engine is old, it's a very good engine and it's easier to adjust than the later models. On this engine you check full power and transition, everything else should be ok then.

Oh, one more thing, remember not to fully tighten the rotating disc screw, the disc has to be able to turn very easily, not free spin, just easy to rotate with your fingertips.
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Old 04-20-2009, 09:01 AM
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Default RE: YS 120 not running right after rebuild

OK, All this info is good.
Now, unlike a 2 needle valve setup, the Regulator screw which affects the transition, the Regulator screw will also affect top end right?
So if I don't like my transition, you are saying that every time I mess w/ the Regulator screw, I reset my top end again before trying the transition?


Help me with my procedure here:
Bring up to full throttle and Set top end slightly rich
Try the transition from idle
If sputtters, then comes up to speed or dies, turn regulator screw inwards (CW) (how much?), then set mixture needle at high end again (slightly rich) and try again.
If slowly comes up to speed, or dies, turn regulator screw outwards (CCW) (how much?), then set mixture needle at high end again (slightly rich) and try again.

I had 15% nitro fuel 20% synthtic-castor blend fuel I was using for this initial start.
I recall running 20%-25% back when I used to fly it.

I also have a gallon of 30% Nitro 20% oil heli fuel left

What fuel should I run normally? I don't need that much power for what this is going into (Scale Spitfire)
If I use 20% Nitro 18%-20% oil, I could use that in my heli as well.
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Old 04-20-2009, 10:28 AM
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Default RE: YS 120 not running right after rebuild

Hello,

First on the fuel, never use any fuel that has Castor in it, actually the maximum allowed Castor in YS engines is 2%, the Castor creates gum on the diaphragm and can clog the internal fuel passages.

Adjusting the regulator, look at it this way, high needle is a regular high needle and the regulator is the low needle.

What I mean by going full power is, once you make an adjustment, do not start the engine at idle and check it right there, instead, start at idle, go full power go back to idle then check.

First set the high needle, unless you are doing dramatic changes on the regulator, (more than a turn) you do not need to reset the high needle at this time.
On the regulator from flush, if it sputters then go cw or closed to reduce fuel to the carb, go 1/8 of a turn a a time or less, after you are rally close go only 1/32 or the thickness or the screw slot at a time, if it slowly accelerates then open it up, don not got 1/4 turn or more, this will only drive you crazy.

Make sure you also have a 1mm opening on the carb at idle when you do this adjustments.

The best fuel I used on the 120 was the wildcat YS 20/20, higher nitro not only gives you more power but it improves the idle a lot. If you can't find Wildcat, then go with fully synthetic helicopter fuel, like Cool Power, Helicopter fuel has more oil in it, and the YS 120 should run on 20% oil.

Which glowplug are you running? and what prop? I used 15x10 APC with excellent results, you can also use APC 16x8

Regards
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Old 04-20-2009, 11:00 AM
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Default RE: YS 120 not running right after rebuild

Thx,
Got it on the needles as you described.
I'll see what prop I have tonight. I know it's an APC, either a 16x10 or 16x8. What ever it is, it ran GREAT years ago w/ it on that plane.
I have an OS F plug on it right now.
I'll see if they have coolpower 20% at the LHS and use that at least next time instead of the castor-synthetic blend.
thx again and I'll report after the diaphram comes in and I replace it. I also got a new plunger and plunger spring just to be on the safe side.
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Old 04-20-2009, 01:17 PM
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Default RE: YS 120 not running right after rebuild

No problem, let me know.
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Old 04-23-2009, 12:52 PM
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Default RE: YS 120 not running right after rebuild

No joy.
I fired it up today at lunch.
First attempt was the same, but then I saw that I AGAIN allowed the diaphram to twist out on installation.
Pulled out diaphram #2 and installed being even more careful this time.
Installed and fired it up.
No air between the regulator and carb this time so looks like problem solved.
There was LOTS of fuel comming out of the muffler but I think that was from when my diaphram was installed wrong since it stopped later on.

But I still have the same problem, I get up to half throttle and it dies suddenly. No girgle, no spudder, dies.
I tried turning the regulator out a turn or two as well as opening the needle to 3 turns but still no luck.
If I turn past 3 turns on the needle, the o-ring seems to show.

Pictured is how I set the timing. Dot on the cam is straight up and the two notches are aligned. I pulled off the cam cover to verify this (put a sharpie mark on the opposite side of the dot since the lifter covers the dot right now.

What else should I look at?
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Old 04-23-2009, 01:08 PM
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Default RE: YS 120 not running right after rebuild

Will it continue to run past half throttle with the glow ignitor still attached and driving the glow plug?
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Old 04-23-2009, 01:25 PM
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Default RE: YS 120 not running right after rebuild

No, it still dies with the NiStarter still attached.
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Old 04-23-2009, 01:51 PM
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Default RE: YS 120 not running right after rebuild

One thing.
I know my tank is holding pressure (at least I think it is). When I called it quits, I let it sit for about 3-5 minutes. When pulling the vent line off to release pressure, I hear the air escape. There could still be a slow tank leak. Could a slow tank leak cause this?
It sure sounds like the high end is lean even though I try it at 2 turns out and it dies.

for some reason 3 1/2 turns out sticks in my mind as to where I used to fly this engine with 30% nitro. But that does not seem right from what I've had others tell me.
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Old 04-23-2009, 02:21 PM
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Default RE: YS 120 not running right after rebuild


ORIGINAL: dditch

No, it still dies with the NiStarter still attached.
That rules out the plug unless it something really wierd is happening.

One more question, after all the work you did on the regulator, did you flush out the high speed needle in the event some crap got sent down the line?
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Old 04-23-2009, 03:09 PM
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Default RE: YS 120 not running right after rebuild

I would also avoid the Byron fuels. I've seen some strange things with the Byron fuel. One guy got a bad gallon once and we fought it for a month and lost 2 planes, only to finally figure out it was the fuel. I would find a gallon of Cool Power, PowerMaster or something else.

Arch
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Old 04-23-2009, 03:21 PM
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Default RE: YS 120 not running right after rebuild

One more question, after all the work you did on the regulator, did you flush out the high speed needle in the event some crap got sent down the line?
DOHHHH, no I did not.
I can unscrew that threaded shaft thingie (needle socket) and clean it out, correct?
That has some o-rings I think and I don't remember changing those out come to think of it.
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Old 04-23-2009, 04:59 PM
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Default RE: YS 120 not running right after rebuild

I flushed out the carb w/ fuel and tried again.
still the same.
I used byron 30% heli fuel.
I also wondered if I put the throttle arm on right. So I loosened it and rotated it 180 degrees and tried agian. same thing if not worse.
Here is a photo of about idle to 1/4 throttle
Is this right or should I rotate it 180 degrees back where it was?
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Old 04-23-2009, 09:23 PM
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Default RE: YS 120 not running right after rebuild

Take the valve cover off and check the valves for the right tappet or gap. While that is apart make sure the head bolts are tight and then put the valve cover back on and if you have a new gasket use it too. You want to make sure all the bolts are tight on that engine and not to have any air leaks at all any where. Just to try it if you can, get a gallon of Morgans Coolpower 30% heli and run through it. As much as you have worked on the regulator area you should have it right. Just start with it flush with the housing and 2.5 to 3 turns out on the main needle and start it again. Let the engine run at a fast idel and get it warm, then slowly start advancing the throttle little by little then listen to it. Try to here how it sound just before it quits. If it sounds like it predetonating then lower the throttle and open the main needle about a half turn then start raising the throttle again. You may have done all this and I'm just typing then. I hope I have helped and keep us posted. I forgot, clean the valve cover bolts good and use good blue loc-tite on them. Make sure you have no air leaks. This thing has go to run

Larry
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Old 04-23-2009, 10:05 PM
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Default RE: YS 120 not running right after rebuild

Dditch,

The notch in the crankcase to use is the one on the bottom of the engine, not top, the engine timing is wrong.
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