Hi All,

Great Forum!

I have a YS 160DZ which came in an airframe I recently acquired. It is supposedly low mileage, but who knows?

On first runs, it was a pig. The main needle had little effect on the full throttle mixture and needed to be at least 4 turns open to have the thing run. I concluded from the reading around that something was amiss, so I stripped it down and cleaned and regasketed the pump, carb assembly, needle valve, rocker cover etc. and did the valve gaps. In doing this I did find a tiny pin hole in the silicon tube from the crankcase to the pump/regulator.

Now it starts fine and appears to run quite nice. Main needle is about 1.4 turns open when richened 100rpm from peak (7700 on a APC 17x12). Fuel is Southern modelcraft mixed to 20% nitro, 1.5% castor and 18.5% ML70. I've tried both YS 4C and OS type F plugs. Exhaust is Hattori cooling header and three chamber pipe. Throttling is stunning (my first YS :-) ), and idle of 2k is fine and returned to immediately throttle is shut.

Now for the but...

After a random period (usually 3 or 4 minutes) it just stops. It kind of dies down, thumps and knocks a bit, then stops. It happens most often at about 1/2 throttle or tick-over. From the way it stops, I couldn't point the finger at rich or lean. More, it has the feeling of the plug being extinguished. I can apply the glow driver again and give it a quick spin and it starts up and runs fine again for a while. I have gone both ways on the regulator, from a very rich and unsustainable tickover to a lovely clean tickover which was sufficiently lean to cause detonation when the throttle is opened, with no consistent change in the quitting behaviour. Behaviour is the same in the airframe (which has had everything replumbed just in case) and when on my engine test stand. Clunk in the airframe is the YS anti-foaming one, although the one in test stand is a normal clunk (but I don't get any foaming anyway).

It was 10degC here yesterday and I did notice a very slight drop in RPM when disconnecting the glow at tickover; not much though, had it have been a "standard" two stroke I probably wouldn't have bothered going to a warmer plug. All the plugs I've tried have been new ones.

Any thoughts?


Thanks in advance,

A


PS all the threads on starting these engines were very, very useful. Especially using a delayed glow driver which makes a big difference.

I'd try leaving a glow driver connected to it for a few minutes just to see if it changes anything. The best way I've found to do this is to connect a remote glow ignitor to the plug, you know, the kind that has a wire that runs to the plug and then a fitting of some kind that you mount on the plane, to which you then connect your glow driver. If you just leave a regular glow driver connected to a YS and leave it running for very long, the head will sometimes get so hot that it will damge or at least distort the glow driver's tip, so using the remote stops that.

This will just give you a little idea of which direction to look. If it "solves" the problem, then you might suspect a rich condition, if it doesn't then it may be fuel delivery related.

I don't think it has anything to do with the engine overheating or of a change in any setting or clearance or anything like that, since it starts agian instantly with no time for the engine or parts to cool. Sounds like a tough one to track down. Good Luck!

David

Now why didn't I think of that? [&:]

Its in the airframe at the moment and has a remote glow on it, so once it stops bloody raining I can give it a go...

(looks hopefully out the window)

Okay it stopped raining...

Started her up (<1 minute, definitely getting the hang of it). Slowly warmed it up, turned off the glow, then gave it 20 seconds of full chat, then throttled back to 1/2 throttle (about 5000rpm). 1 minute 10 later it coughed and started banging away about to stop, so I immediately turned the glow back on and viola immediate sweet running again. I repeated this two or three times. So I agree its a problem with it richening and cooling the plug.

So I spent some time tinkering. Ooo, it's a sensitive little bugger. Going 1/4 and 1/2 turn richer on the regulator definitely aggravated the problem, reducing significantly the time before it would quit. Finally, I have ended up with the reg about 1/4 turn leaner than it was. At this setting, it seems to run consistently for >30s at a variety of throttle settings. There is a hint of hesitation when opening up and if left to idle for too long it starts to speed up a little, then it starts surging and eventually stops. So I'm guessing it's still 1/16 to 1/8 turn lean - it's gone dark and I've just run out of 20% nitro so it'll have to wait to the weekend for a bit more running and confidence building. If I go another 1/8 turn lean from where it is, transition is very poor and the needle is insensitive at full throttle, so I don't think there's much point going any leaner.

Do these behaviours and degrees of adjustment sound normal? If so can stop questioning whether there is still "something wrong" and get on with tuning some more.

Well, it was a lovely afternoon, would have been rude not to go flying, wouldn't it?

Pleased to say I've just had 4 x 12 minute flights (pretty much empties the tank) and not a hiccup or cough from the engine throughout (and it was only 3degC ambient). It seems leaning the regulator slightly has done the trick - I didn't change any settings from where I finished up yesterday.

Thanks again for the help.

Glad to see you sniffed out the problem. My advice would have been to start with leaning the pump 1/8 turn at a time to try and make it go away because the description sounded like it was doing exactly like you suspected, extiguishing the glow plug.

The very fine adjustments are typical of a YS engine. Not everyone has the patience or the finesse to be able to own them and fly them, but for those who do they are in a class by themselves. Like most any high-performance, high-quality piece of equipment, it's best to use tweezers insted of a hammer to adjust them, if you know what I mean, and not everybody can do it.

Glad the glow driver idea worked for you. I used to repair small engines for a living (lawn mowers, chain saws, etc.) , and most of the time 90% of the difficulty in repairing one was in diagnosing and determining what was wrong, not in the actual repair itself. So you learn to think along the lines of eliminating some of the possibilities. Once you know what it "ain't", you can begin to focus in on what it is.

Anyway, glad it worked. I, too, suspected it was rich, and that was the best way to test it out. Happy Flying!

David

In my very limited experiance, I own 2 YS motors, 63 FZ and 120 SC, and both of them exhibited similar kinds of issues when brand new. Surging, poor running and stopping, just like you expieranced. However, the more running they had, the better they became. I did have to change glow plugs early on as new engins tend to eat plugs.. But now they are properly run in, I don't change any settings at all, no matter what the conditions. Just fill up and fly.. Easiest engines to operate I've ever owned. I think new engins just need a bit of fuel through them to settle down.

I used Troy Newmans set up method to tune them initially, http://www.patternflyer.com/troy/?page_id=13 which gets you in the ball park, and then very fine adjustments untill they run like a swiss watch. Easy. Like David, I think alot of people are ham fisted with tuning and get frustrated, especially when the engin is new and still setteling down. Just have patience and adjust cautiously..The grunt these YSs' can produce is worth it.

Roger

Thanks again guys.

I'd looked at Troy's page but it's only relevant to the pressurized tank variants.

I guess what caused me to question in this case was the fact that, at the settings I had arrived at, it actually ran lovely at all throttle settings and had stunning transition. Every other 4C motor (all non-YS and all 1.20 or smaller) I've owned would let you know the out-of-adjustment by being noticeably rich or lean in some way (burbling, 8-stroking, hunting, sounding "hard" etc.), but wouldn't actually stop. With this being a bigger and better metered engine, I've learned that it can sound fine but still not be optimum and am now expecting to fine tune in the air over many hours of gentle tinkering, I'm sure there is even more performance to come.

A