Hi Dave,

I have a YS 120NC that is mounted inverted in my World Models FunWorld FunFly 3D. The engine doesn't want to idle down too well and overall it runs quite rough.

I've turned the regulator in a turn or two in an attempt to smooth out the low end. when I remove the glow igniter there is a noticeable RPM drop and increase in the roughness. How can I tell what the proper setting should be?

The engine is not running lean, but it always feels hot to me after a 10 minute flight. I've richened the high speed needle as I screwed in the regulator. I am running an APC 17X6 prop and am not exceeding 8500 RPM...

Also, the mid range is very rough and it doesn't smooth out until full throttle. It's mounted on an antivibration mount and it moves around quite a bit in the mount. At half throttle the regulator screw is just a blur...

I've already had it in for service in the last month so I know the gaskets and silicone parts are okay...

Any suggestions?

TIA for your help.

What fuel and plug?

I am using PowerMaster YS20/20 fuel and an OS F plug. I recently replaced the plug with not noticeable effect...

Does this engine have an idle air bleed needle or is it fixed?

As far as I can tell it's fixed. The instructions that came with the engine instruct me to turn in the regulator to lean out the low end mixture... I've read about some hole somewhere on the carb that is often times enlarged on the 1.20NC engine. Is that what I am facing? Is there a replacement carb available that has a proper low end mixture? Also -- what about the roughness? Is this all related?

Leaning the reg will just screw up the transition. The bleed hole in the carb barrel (remove it and you'll see) will need to be drilled out slightly. Go a little at a time until the idle is OK. They are all different so I can't tell you exactly what drill size to use.

Hi Dave,

I took the carb barrel out last night and before I drill out the hole a little I wanted to ensure that I am looking at the right hole. The hole I am planning to drill is the hole through the flat spot of the barrel that is on the side that you cannot see when it's installed. The other hole that I can see bisects that axis of rotation and can be seen in the groove that the retaining screw fits into. I was not planning to drill out this hole. Do I have it right? You do carry this part in stock in case I mess up-- right?

The one in the blade is the right one, you had it correct.

Hi Dave,

I drilled out the hole in the butterfly valve to 3/32 and opened up the the regulator. The engine is running better and will idle well at 2400 or so and was topping out at 8400 or so with an APC 17X6. I am certain the engine is very rich, but it feels like it is getting hot... So far I have about a gallon of fuel through this engine and I am unsure how broken in it was when I got it...

It is still a running rough, but it is better, and I was wondering just how smoothly this engine will run -- inverted? I am also curious as how I will know when the low end is correct... I usually rely upon having no RPM drop when the glow driver is removed added to several minutes of idle with a clean transition to full throttle... Does this sound reasonable?

TIA for your help.

None of the big YS engines are what you would call smooth. They all vibrate a bit. Upright or invert doesn't make a difference.
RPM drop when you take the clip off indicates too rich or poor quality fuel. You may have to go bigger on the drill size on the air bleed.
The low end is correct when it will continue to run without leaning out or richening at idle. If it takes the throttle ok it is close.
If you think it is running hot, reduce the load with a lighter prop. You can run these at 9000 with no problem.

Hi Dave,

I have another gallon through this engine and am getting a little leaner on the top end and the power it starting to come up too. It's still a fat on the low end with the butterfly valve drilled to 3/32" and the regulator screw flush with the housing. Before I go up to the next size in my drill index, 1/8", I wanted to make sure that it's the right thing to do. Is 1/8 too big? Can I get the lower end leaner with the regulator? The mid range seems fine and throttle response is great. It still shakes a great deal on the low end though...

TIA for your continued help!

Try going in on the regulator first. If that doesn't do it, go to 1/8"
Shaking at idle is pretty normal.

What precent fuel are you running ? and why may i ask are you swinging a 17x6 APC? try a 15x8 APC! thats what I run on all my YS's also found that they run best on a McCoy plug. I would start at the high end needle about 2 turns out and and maybe 1 to 1 & a half on the low end. and go from there, sounds like it may have some dirt in there also. I've noticed when i buy a new YS they always seem to have just a little tiny piece of dirt somewhere

I came on line this evening after a nice day at the field with the EXACT setup you are using (YS1.20NC and WM Fun World 3D). What you describe is my condition.

I have two YS 1.20 NCs. The first one, purchased about 6 years ago is from the outside identical to the one that is now installed in the World Models plane. The one installed in the WM is about 2 years newer than the first one.

THe first engine runs like a clock. Contrary to one of the posts, your expectation should be that the YS will purrr. Transitions should be immediate and completely smooth, idle should be stable even when very, very slow (so you almost hear the valves ticking away), and you should be above 9K RPMs turning a 16 x 8 APC (what YS performance recommends and seems to optimize the power curve on this engine). Like one of the other posts, I also used to run a 15 x 8 but the thrust is more with 6 x 8 when doing the back-of-the-napkin calculus (raw feel).

Anyway, the reason for the engine history is that the second YS never ran well...from the start. I had sent this to YS performance (after being so happy with my first one) and they drilled it out as the recommended cure. Apparently there were a bad batch of engines out there that would never lean or richen (I can't remember now which way it was).

After the drilling (side counted at the time) it did run better but still nothing like the first engine. Now that it is mounted inverted, it does exactly what yours is doing (vibration, etc). I have a little rpm drop off when the ignitor is disconnected but no severe. My main problem is the transition. If I goose it it really stumbles.

We tinkered with the high and low (I never even thought of touching the low on my first engine) and honestly, I couldn't tell when it was running better or worse.

I was actually hoping to come on line to find the direction I should be turning the low end as I probably have it all messed up now.

I will stay tuned and let you all know if I find something out.

Trevor Dearman

Yep, got a bad 120NC also. Been sent in, still runs bad. After a brief retirement from modeling, had to replace some bearings. Had to cut the bearings of the shaft with a Dremel cutting wheel. Couldn't get the new ones on until I had the crank machined to the correct diameter.

I don't think this engine will ever run right. Going to saito 180!!

ML