garrett_mcdonal

Hi Guys,

I picked up a 2nd hand pattern ship recently with a YS-120 in it. It appears to be the same as my FZ-140, except there is no nipple on the back of the crankcase. I assume it is the SC model.

Anyway, here's the problem. It has been running quite well until the last day or two. Today I had to wind the high-speed needle in 1/3 - 1/2 of a turn from where it normally runs to get the rpms to peak.

On top of that, the bottom end seems slobberingly rich all of a sudden. If I let it idle for 15-20 seconds and then go to accelerate (even slowly), it labours and gurgles and blows fuel and lots of smoke for some time before the power comes back on.

I tried leaning the bottom end out, but it just didn't seem to be having much of an impact. If I let it sit there at idle, it just keeps loading up with fuel. The idle rpm slowly drop away until it is very rough. To me this suggests the bottom end is still rich.

Any suggestions? What are most people using as the starting point for both the low and high-end needles?

Thanks,
Garrett

Geistware

My Feedback: (16)

Did you change fuel?
If this happened between tank fulls then it seams that you fuel has changed.

garrett_mcdonal

Geistware,

Nope, it seemed to happen mid-way through a container of fuel (20/20 that I have always run in my YS engines). I have some time off work at the moment, so I've been flying every 2nd day for the last week and the fuel was less than a week old.

I swapped my FZ-140 into the model this afternoon and it seems to be running just fine on the same fuel.

I need to get more fuel tomorrow, so I'll mount the 120 up on a test stand and see if it is any happier.

Any other suggestions? If not, I'll send it in for a service. I know the previous owner and although it has been very well looked after, I'd say it has done a lot of time and is probably due for an overhaul anyway.

Regards,
Garrett

garrett_mcdonal

That reminds me, if anyone out there can remember the real-world base settings for the low and high end needles in their YS-120s (rather than what is in the instructions), please let me know.

Thanks,
Garrett

garrett_mcdonal

Hi Guys,

I ended up sending my YS-120 in for a service. They confirmed what I ended up suspecting, it was a regulator problem.

Apparently, the diaphram material had hardened and was causing the engine to run erratically.

So, there you go. If your YS starts running like a pig and no end of needle tweaking seems to make a difference then it could well be the diaphram.

Regards,
Garrett

PineBaron

My Feedback: (38)

Initially, remove the regulator screw, remove the valve and generally clean the area of any particles. Assemble and screw the regulator screw flush with the housing.

Only the 140 has nipples on the back of the crankcase. The 120,91 and 63 do not have these.

In my own experience there have been one of two reasons for the problem you have.

1. Fuel blockage (simple, just clean as described above)

2. This is nasty: the front bearing gave way and the engine will appear to have those low and high end splurging problems. I had the problem on a YS91.

Else, place a question on the YS engines manufactureres forum to Dave from YS. Dave will give you an answer; more than likely he may ask you send the engine to YS for service

Vim

garrett_mcdonal

Vim,

Thanks for the reply. The service guys indicated that the diaphram was stuffed and that this can cause erratic behavior.

To the best of my knowledge, the bearings had been changed recently before I picked up the engine in a plane. I know the previous owner and he is meticulous about equipment maintenance.

It should be back some time in the next few days, so I'm keen to see how it runs.

Garrett