T-ster

My YS 1.40L has quite a bit of time on it, but recently sent it in after a crash. All was good with it other than the bearings which were replaced. I've ran it several times since with good results but now it is inverted in an Ultimate (never have had it inverted before this plane) and it will appear to run pretty good then just stop. Restart it and runs ok but will again just stop. (I don't have a fuel filter on the plane.)

When I went to fly it today, the temp was 42 degrees and it wouldn't do a thing, just spin with the starter and nothing. Fuel was getting to the engine as it was dripping from the carb. Finally I ran the throttle to full and got it to bump a few times, then it finally started and I got a decent flight in.

When I went to run it dry, it wouldn't bump again. I only tried a few times, but gave up.

Any idea what this could be?

petec

My Feedback: (58)

If compression feels good, tank is holding pressure and the valves aren't sticking....Just for grins put a new OS F or YS #4 plug in it.

T-ster

Sorry, should have mentioned that. Using an OS Type "F" plug and replaced it during this ordeal and it made no difference.

I was wondering if a valve was sticking, but they appeared to be ok when I took off the valve cover and turned the engine over by hand.

There was very little compression though. Was easy to spin the engine. Normally when it is getting a bump, there is much more compression.

petec

My Feedback: (58)

Much needed info. Low compression can be one of two things, valves not sealing or ring is just worn out and not sealing. You said the engine has quite a bit of time on it and has been run since the bearing change. When did the compression go away? Anything change like what fuel you were using? That might cause carbon build upon the valves causing them not to seal when seated. You can look in the exhaust port and see if it s carboned up...also prop the engine over slowly by hand and listen for where teh air from the compression stoke is leaking out from...exhaust port, intake port, or throttle bore. If it's either one of the ports the valves are not sealing when seated and the throttle bore would indicate the ring.

T-ster

It received a clean bill of health w/ only bearings needing to be changed. Even though the engine is fairly old, I don't fly long flights or very often, so I suppose you could actually say it has very low time (compared to others). I would have imagined when I sent it in they would have checked valves, carbon, etc. I received it back around 4 months ago and have only ran the engine 5-6 times since then.

Compression appears to be ok checking it at home.

I'm going to try and fly this afternoon.

Thanks for the comments so far!

T-ster

Well, it ran quite well today. May have been something in the valves. Still need to adjust the low end slightly, but overall there is hope!

petec

My Feedback: (58)

That is good to hear.

still4given

My guess is that there was some foreign matter in the regulator. It was probably letting too much fuel pass and flooding the plug. Starting at full throttle is an indication. You really, really need to run a fuel filter on the YS engines.

T-ster

I had forgotten, but actually do have a filter on the fuel line. Guess I didn't look to close when I installed the darned thing......

T-ster

It has been starting reliably ever since my outing a week ago. However, the engine is not reliable.

Starting from the beginning:

I sent my YS 1.40L in for service a few months ago. They replaced the bearings, but said everything else was good.

After I got the starting issue taken care of, I thought the needles needed to be tweaked. (The engine is inverted with an OS type F plug and 30% Cool Power Heli fuel.) The idle will be high or low, at different times. At idle it sometimes sounds like it has a suction cup popping type sound (like a suction cup when it releases) I will leave the glow attached for 20-30 seconds and let it warm up some (it was 72 today) then disconnect it. It may slow down just a touch , but generally run ok. If it is running at low idle, high idle or slightly more it sometimes just stops. Not like it is loading up or leaning out, just stop. Other times it will be running fine I go to take it to the runway and then stop. It almost always starts right back up. The low speed is at 1-1/2 open, high speed at 2-1/4 and the diaphragm is about level. (This is my 3rd YS four stroke, so I have some previous experience with YS's. )

If I have the engine running at 2,000 rpm it will vary between 1,850 and 2,100, but not be as smooth as it used to run. If I try to lean it, then it will start to pick up rpm's after a few seconds. So I believe the idle setting is very close.

When running around 3-4,000 it will be smoking and rich but running good, then up and stop and at times fuel runs out from the carb. I then lean the diaphragm and it will start to pick up rpm after sitting at 3-4,000 for a second or two and stop smoking. That is only leaning the diaphragm very slightly (I know they can be touchy).

A knowledgeable club member listened to it today and was sure the timing was off by a tooth. How do you check the timing and adjust it? Pull off the round plate at the base of the pushrods and the dot should be center or just left of center at TDC? I checked when the piston is at TDC and when both valves are closed the indention on the cam gear is at the top with the cam lobe down and to the left (see photo).

I'm getting a lot of fuel around the back of the engine (from the carb I would assume) during running or after shutting it down.

I have pressure after running it, so believe the fuel lines are ok, although I am going to change the ones out on the engine since it is handy. Since it was apart, I checked the valves and they were fairly loose. I had to turn each of the adjusting screws 1 turn each to get them to spec.

That is all I can think of for now, but sure I've left some stuff out.....

Advice?

Thanks!

petec

My Feedback: (58)

I wouldn't worry about the timing for one reason, Richard and his crew run each engine before it leaves and they would have caught it.

You may want to check your regulator plunger and diaphram since you say you are getting alot of fuel out of the carb.....unless it isn't coming out of the carb bore and the carb and backplate are little loose which will give you a vacuum leak that will drive you nuts trying to tune your engine.

T-ster

The saga continues.......

Ran it two weekends ago in the back yard and seemed to run very well after making adjustments. Full throttle with the wood Xoar 18x6 was 8,500. Would bring it down to 4,000 and it would vary +/- 100 rpm (TNC tach) so real good. Idle at 2,000 rpm and would vary +/- 100 rpm, running pretty good.

Took it to the field today and same darn thing. May or may not run well but typically above 1/2 throttle will run great. It started off running well, then after I picked up the plane and started walking to the runway it simply stopped. Took it back and it started right up. Same thing again when I walked out to the field. Tried turning the regulator out and back in to the same place and didn't seem to make much difference. Started again and same thing, but on the starting table. Next time I started it, there was not much smoke at all which was kind of odd. After it stopped again, it started right back up and then had the normal amount of smoke.

The symptoms are typically the same, running pretty good but when it gets less than 1/3 throttle it sometimes runs good with no problems at all, other times will run fine for anywhere from 2 to 20 seconds then simply stop. It doesn't sound like it's loading up or getting lean (most of the time, although this can sometimes vary), just stops.

Had someone else carry it to the field to make sure I could mess with the throttle as necessary. Ran up to full throttle on takeoff and was running great. Flew a couple of circuits at anywhere from idle to full throttle and was responding well. When I came back to 1/3 throttle for 5 seconds this time (which I had done before) it just stopped, deadstick again......

A few things: 1. The fuel tank has no cushioning around it as it is in a World Models Ultimate and the fuel tank fits just inside the formers without much play at all. 2. The engine is soft mounted with the mount that came with the kit. 3. The tank is holding pressure fine. 4. It is inverted. 5. Running high speed needle a few clicks rich of max rpm.

I wonder if it has anything to do with no tank cushioning or the soft mount engine, but it varies on when and where the issues occur. I haven't changed the diaphragm out, although I did remove it and it seemed ok. I will have to order a diaphragm which is why I haven't already tried it (guess I should go ahead and get that on order).

I'm getting fed up with this darn thing!

petec

My Feedback: (58)

1) When you are running it at home and it's behaving is it in the model?

1a) Too soft of a mount and how the servo and pushrod are set up can cause a LARGE fluctuation at idle and even cause shut down.

2) How is the transition from idle to full throttle? That is where your regulator setting comes into play.

Read this for a bit of help with the settings:
http://www.julton.net/Fact%20Sheet%20YS%20Engines.html

3) What happened to the fuel you said was dripping from the carb?

T-ster

1) When I ran it at home it was in the model.
1a) I was concerned about the soft mount with the pushrod changing the throttle setting, so I can understand somewhat of a variation however I'm sure that is not the issue.
2) Transition is typically good. Thanks for the link to the article, but that is the exact article I've been using to tune the engine.
3) Still get some fuel dripping at the end. It's not because the carb is loose, because I took it off to check timing and all the bolts were snug when I removed it and the gasket was intact.

I also changed all the fuel lines on the engine the last time I had it off the plane, which didn't make a difference.


Should I get a new diaphragm and check valve? Could a problem with one or both of those cause these kind of issues? (It's holding pressure, but who knows what the heck is happening at this point.....)

petec

My Feedback: (58)

Yes and yes to the check valve and diaphram.

T-ster

Boxed it up and sending it in to Richard for his review. I'll be anxious to hear the results.