Pete S-RCU

I have a YS 140 sport that quits in the air.
Engine is 3-4 yrs old, used to run great.
Using Wildcat 15% fuel, 16x8 MA prop.
Needle valve hard to adjust, runs leaner than it used too, no smoke trail.
If I richen it up for a nice smoke trail it will quit after a few minutes running.
Replumbed the tank, all new fuel lines, filter is clean.
I notice air in the line from the regulator to the carb, is this normal?
No air in the line from the tank to the engine.
Replaced the diaphragm, it was OK.
Tank will hold pressure for a long time after shutdown.
Engine was in a crash, replaced carb housing on back of engine, new gaskets etc.

petec

My Feedback: (58)

When does it quit? Idle? Half throttle? Full throttle? After it gets hot or when it is only running for a minute? Can you get it quit on the ground?

Why is it running leaner? Is the intake tract sealed? Are you sure the gaskets and o-rings are sealing sine the throttle housing replacement?

Pete S-RCU

It quits in the air or on the ground, at full throttle.
hot or when it is only running for a minute, doesn't seem to matter.
When I try to adjust it on the ground, as I richen it, it sounds like does when it's lean and ready to throw a prop, but there's lots of smoke in the exh, so it must be loading up.
I set it lean enough to run, and have made a flight or two that way, but I know it sb richer.
I have three YS engines and they run best with a good smoke trail.
I think I'll disassemble it today and check the gaskets and O rings to be sure they're OK.

petec

My Feedback: (58)

Also you might pull the whole needle valve assembly and flush it out with raw fuel. While its out crank the engine with fuel in the tank and let it flush the fuel line and carb body out in the event there is something in there causing a blockage.

If none of this results in a find, did you disassemble and clean out the regulator?

Pete S-RCU

Yes, I did clean everything out.
I've noticed the engine quits on an up line?
Runs best at 1 1/4 turns open, used to be 1 1/2 or maybe a little more.
Now, if I try to get it to run at 1 1/2 it spits and quits, sounds like it's lean and going to spit the prop off?
Not sure what's going on here?

MajorTomski

I know this is for factory support but there are thre things that haven't been mentioned yet, and are easy to try before he starts tearing the engine down.

Is your fuel fresh/good? I had a YS91 that gave me fits till I just bought a bottle of fresh fuel.
Around here in Oklahoma the YS Four strokes seem to be happiest on 20% nitro or more, I noticed you're using 15%.
Is your prop on really, really tight? I had similar problems with a prop that was slipping.

MTC YMMV. Safe weekend.

Pete S-RCU

Fuel is brand new Wildcat 15%, have used this for years, can't tell much difference between that and 20%.
Prop is really tight, learned that the hard way.
I have two YS 120's that run perfect foe years now, the 140 has always been a little temperamental.
Only reason I'm using the 140 is it's a bolt-in replacement for the 120's.
Don't make 120's anymore.

spaceworm

If it quits on an upline, maybe the clunk in the tank is folded up toward the front of the tank. It may be immersed in fuel when level or downlined, but sucking air when on an upline. have you had a rough landing or crash lately where the nose came to a sudden stop throwing the clunk forward? Happened to me once and drove me nuts till someone suggested to hold the plane nose up before putting it down on the runway to takeoff. If it stops, you know you have a fuel draw issue. Maybe check the tank plumbing.
Sincerely, Richard
AMA 861960
Club Saito #635; Saito 56, 100, 120abc, 130T, 180
YS F-120;

petec

My Feedback: (58)

Did you look at the needle valve taper? If you run a needle valve extension the weight and the vibration will cause it to wear abnormally. YS engines don't just change tune for no reason. It could be glow plug, needle, bearings, or regulator.

Nitro content just makes the engine easier to tune, 15% is fine as long as it has 20% oil package.

Have you pulled the engine and put it on a test stand?

Make sure you have a YS #4 or an OF F glow plug.....accept no substitutes.

Pete S-RCU

needle valve is new, glo plug is OS-F.
Have run it in the plane, on the bench.
Tank holds pressure a long time, an hour at least.
Problem is when going up in a steep climb.
Also will falter if I try to richen the mixture on the ground.
After all the cleaning I did, seems better, will have to fly it to be sure.
Needle valve is very sensitive. have to adjust it very slowly.

Dave Harmon

If the fuel feed line inside the tank has a split near the metal tubing....when the fuel level uncovers the split such as nose up or level with a half tank or less....
It will go lean and quit.
Also....under G-force, fuel line anywhere can flop around and open a split causing a loss of pressure....and go lean...then close up again.
I have had to use Du-Bro fuel line since Prather went out of business and that DB fuel line is so soft and full of debris that I have had a lot of trouble.
The DB line has chalk or powder inside and small silicone chips too. The chips are just about invisible if they get inside the n/v area.
I started flushing all the lines before installation but it is still prone to splitting....I hate that stuff.

Also....weird problems can be caused by a worn out piston ring causing some blow-by which upsets the crankcase pressure which in turn affects the mixture.
Is your engine a 140 Sport or the earlier model?
Does it have the 4 holes or slots on the outside circumference of the piston??
The earlier 140 did not have these holes and was a local mod done by YS Performance.
The 140 Sport came from the factory with 4 slots. The compression of the piston went through these holes and pressed the ring against the cylinder.
This caused much better ring sealing and much of the weird problems went away.
You should check to see which piston you have...you can remove the plug to look into the head to see the top of the piston.

Pete S-RCU

Good suggestions Dave, I'll check it out.
Mine is the 140spoirt, but I'll check on the holes in the piston.
Maybe time to replace all the fuel lines.

Pete S-RCU

well, it has the new piston.
In desperation, I screwed the regulator in about two turns.
I know, you're not supposed to mess with it, but what do I have to loose?
It runs much better now, nice smoke trail, so I think I'll leave it that way.
Any ideas what this means?

lasers200

As they age you have to run pump richer so getting closer to rebuild. Run it till it acts up again.

kenh3497

I may be wrong but turning the regulator screw IN should reduce (lean) the fuel flow???? OUT should make it richer?????

Ken

petec

My Feedback: (58)

In on the regulator does lean it which may indicate the regulator spring may be weakening. BUT before we go down a rabbit hole....what changed? If the engine is 3-4 years old how much time is on it? Did it sit for 3 of the 4 years? Has it been flown a lot for all those years (like pattern guys are apt to do just to get better). YS engines don't just change tune by that much without a reason.

Two full turns on a YS regulator is a lot of change from where it was for a long time which makes me ask, what changed?

If the engine has a lot of fuel through it, a trip to Richard may be in order.