Hi, Dave,

I just got a used YS 120, and have a few questions to ask.

It has a shaft key on the crankshaft. When I check out the Central Hobbies website for parts diagrams, NC & SF both has the shaft key and no idle needle. Looking at the intake valve, there is no small holes arount it. (Only disassembly was the carbbody removal).

Do I have an SF or NC?
SC part diagram has the idle needle, so I don't think it is an SC. It surely is not an AC.

Any idea?

Also, it's been ran for around two seasons from new and been stored for the last two years.
I am going to replace the diaphram as I have a couple of them as I have a 140L.

What else would you recommend to replace? After removing the carburetor body, I could see the main bearing does not have any rust. Just oil residue (brownish). Complete removal is planned and this engine will be installed in an Excelleron 90 from Sportsman Aviation using a YS 140 Sport' muffler.

What size prop do you recommend for this engine using Magnum DZ fuel (30% nitro w/ heli oil) around 1000 ft elevation?

Thank you,

Ihncheol Park

Sounds like an SF. Does it have a deep, round recess at the center of the backplate with a socket head screw in the middle?

If it has sat this long replace all the o-rings, diaphragm and gaskets just to be safe.

Prop size 15x10 to 16x8.

Dave,

Yes, the carbbody has a hole in the middle and the back plate has a socket head screw which holds the disk valve.
I guess it is an SF.

Is there much power differences between the each YS120s? SF, AC, SC, NC, FZ?
Should I keep the top rpm range between 8k ~ 9K?
Thank you,

Ihncheol Park

The SF was the first and least powerful, but a great engine. A 15x8 or 16x6 prop should be about right.

I have been tryin to ID this YS-120 for my brother any thoughts?

Either an NC or an SF. Need a shot of the rear to tell.

Here Dave- Thanks in advance!

SF. Probably second version. Great, reliable engines. Wish we could still get them.