I'm about to drain the oil and take off the cover to inspect clutch on my ATV and I've got Valvoline synthetic 10w30 to out back in it.
I've seen some people say that will work just fine while others day absolutely not you have to buy Kawasaki brand oil or ATV specific oil.
The service manual says

Can someone tell me if this will work or is there a special oil to use?

 

As it says on your chart SE or SF quality. Any oil suitable for motorcycles should have this marked on the tin. Because the KLF400 has "wet" clutches like almost all ATVs and motorcycles, the oil hasn't to contain certain friction inhibitors. Check if the Valvoline tin has either "suitable for motorcycles" or SE or SF on it.

 

Alrighty, Saw another poster say SE and SF was a outdated term no longer used on oil products so wasn't sure about that.
What I've got is Valvoline synthetic high mileage SAE 10w30

 

Is it the Valvoline ATV/Motorcycle oil? Walmart sells that for about $4.79 a quart.

I wouldn't just use car oil in it for the slight savings you get. If it messes up your clutches, you will be wishing you had just spend the $15!

Just saying...