I purchased a YS 91 AC. It is supposed to have a new diaphram and gasket set. It will not run properly. You can actually drive the high speed needle all the way in and the engine will not die. I have never had a glow engine act like this. Does anyone know about this engine? I have never had a YS. I started at the factory settings for the low and high. 1 1/2 turns out on each. It will start at that point but not run right. As I mentioned something doesnt seem right with the high needle. Also there is an O-ring near the carb that seems to be leaking fuel.
Any advice would be appreciated.
Thanks
Darren

I fly a used 91AC and two new 110FZ's, and have a 160DZ on order. YS's are awesome performers and are actually quite easy to tune when they are running right.

YS's need a special fuel line setup to work properly, so make sure that your fuel lines and check valve etc. are hooked up exactly as recommended.

You may have some sort of leakage somewhere in the system which is quite complex and must be perfectly sealed in order for the engine to work right. Or maybe the new diaphragm wasn't installed right or the plunger is sticking. I'd start by checking the fuel system and taking care of the leaking O-ring.

You might want to try posting in the YS support forum and be more specific with the symptoms. Will the engine run correctly at full throttle? Will it idle? Does it want to load up or lean out?

Walt

Hi Walt,
The engine will run up but it sounds a bit rough. When you turn the high speed needle in it does not change much. Also as I said, you can turn it all the way closed and it will keep running.
Do you know if it should keep running with the high needle in all the way? Does that say there is something seriously wrong? An air leak? Maybe that is from the leaking o ring?
Thanks
Darren

When Y-S engines are in good shape there is absolutely no engine that runs better. They have perfect idles and make power like a engine a size larger than they actually are.

But one giving trouble is a nightmare. The screw on the regulator should be flush with the outer edge of the regulator body.

The regulator has a spring and a viton valve plunger in it as well as the diaphragm. There's no telling what was done in there.

Your engine most likely has the wrong needle valve in the carb. The carb is a air bleed type and the wrong high speed needle adjustment will also effect the idle.

If I remember correctly the AC version has a different needle valve than the FZ version. The FZ 110 is the current production model. The AC 91 has been around for a while and the carb is different than the FZ.

Enjoy,

Jim

Darren,

My YS experience is still pretty much limited to engines that don't have any problems and unfortunately it sounds like yours definitely has some issues.

It sounds like yours is running rich no matter where the high speed needle is set. Opened up fully the high end is adjusted pretty much like any other 4-stroke. Except I've found on a YS that if it is too rich it will tend to load up and sputter a bit. The high needle on my 91AC is exactly 1-1/2 turns out. If your engine has the wrong needle valve you should be able to get the correct on from from Central Hobbies.

The idle adjustment on my 91 has no affect on things except at when the engine is at idle, and it is not a very sensitive adjustment.

The regulator adjustment controls the spool-up mixture. Its not all that sensitive an adjustment either, so don't be afraid to play with it. On the rich side the engine will put out a ton of smoke when the throttle is opened up. Closing it off reduces the smoke. But the engine should run OK as long as it is set close to right. Start with it flush to the body.

I think that the plunger/regulator on my 91AC sticks a little sometimes when I haven't flown the engine for a while. It loads up, coughs and sputters. But once warmed up completely everything clears up and there are no more problems for the day.

Walt

One more thing, make sure that you are using the right fuel. Everyone I know around here is running 30% heli in their YS's. I never tried it but I understand that YS engines run badly on 15% or lower nitro fuels. And I also understand that fuels with low oil content or castor in them can cause all sorts of problems. So 15% Omega, Coolpower and the like are not at all appropriate.

Walt

Hi Jim,
I called YS and they told me the whole assembly may need replacing. They told me they dont make the part anymore but the new part will fit. I am guessing that is for the 110. He told me there is a brass fitting where the needle goes that maybe worn.
Thanks for the help
Darren

That's what they had to do with my AC. When they were done, it was a FZ all over.

Enjoy,

Jim

I was hoping to be able to install the part myself. I havent looked at it as I am at work and called them from here today. I guess I will look and see how hard it is to install myself and go from there.
Thanks
Darren