I have two OS 160 twins and have found the ONLY way to get a reliable way to get this engine to run properly is to use a Perry Aeromotive Oscillating Pump mounted to the front engine bolts. This will place it just about under and behind the carburetor. I used a 1 1/2" wide flat piece of aluminum long enough to reach both front engine bolts. You have to cut a U-shape out of the aluminum to fit around the bottom of the engine to get it too mount up to the engine bolts. I have taken a picture of my C-182 without takeing the cowl off too maybe show you.
Of course glow plug heat is also a must and helps...but it is a fuel draw problem.
Jim