I just finished installing a new YS63, my first 4-stroke. I put an OS F plug in and installed a prop.

Shouldn't it have some compression? I can just rotate the prop around with a finger.

I'd like to fire it up tonight, but this seems odd.

Thanks,
Chuck

Sooner or later you will need to learn valve adjustment. Might as well check it right now . It should be very close to spec,if not just follow the directions.

Great choice!!!

This isn't all that unusual for a new engine...it's probably the ring not being seated yet or a valve is sticking a little. My YS 120 almost free-wheeled for the first gallon or so, only having compression when hot until everything was broken in. An electric starter was able to get it going when new and now it has excellent compression and runs great.

After checking the valves, run it through several tanks and you'll see the compression gradually improve.

Make certain that you do not hurt the gasket on the valve cover and that you secure the valve ccover back on properly.

The Y-S engines use the crankcase to supercharge the incoming air and the space around the valve cover is used as a plenum chamber for the intake before the intake valve. If you have an air leak somewhere including the valve cover, it will drive you nuts till you figure it out.

Jim

Thanks everyone! Everything is okay. I thought maybe a valve was sticking so I filled the tank and flipped the prop a few times. I had compression right away.

So I fired her up. Nice motor! I have it in my Pizzaz for break-in, and I'll fly it tomorrow.

And when I went to empty the tank I got a nice shower! I read that you should open the vent fuel dot first, but I sorta forgot about that.

Thanks for the help!

Chuck

Not all that uncommon for a little swarf to hold the valve slightly off seat
You should be very happy with it. I couldn't wipe the grin off my hubby's face after he flew his first YS