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.