Casement Window Won't Pop Open with Crank

[AndrewGT]

I have a window similar to this:

My crank works great if it's open, even if it's only a tiny bit open (even if it's almost pressed closed). But when it gets pretty much closed, I can no longer move it with the crank. I have to give it a tiny push with my hand, then it pops out and I can control with with the crank. Any idea how I can deal with this, so that I can open it with the crank?

 

[Snoonyb]

Lube it.

I use SLIP-IT, non silicone spray on the lever arms and faucet lube on the crank mechanism.