I have this 70 that is running great, most of the time. When on the bench, it will rev to full throttle and run great, but when in the air on my Somethin Extra, it will run half throttle at times, even though the carb is WOT. However, I didscovered yesterday on the stand that if I rev the engine up and down and go WOT it will run at half throttle, same as in the air.

What I have seen so far, and not sure if related, the drain for the crankcase is not plumbed, so there is a lot of oil getting blown back at the firewall, so maybe its ingesting that and causing the problem? The other thing to note, the HSN wiggles, and with the engine off if I wiggle it I see air bubbles in the fuel line. Since the spring broke off the needle, I ordered a new assembly, so that should correct that.

Could either of these things be causing this?

The open breather is of no concern at all. It would not cause your engine's difficulties. The wiggling needle is of concern. It is likely leaking air and causing the erratic running. You may also want to check the carb body to make sure the needle seat is not damaged.

I have a replacement needle package on the way, should have it tomorrow. Its the whole thing that screws into the carb, not just the needle itself. Since the spring got busted off, might as well just replace the whole thing. I still want to move the drain away from the motor, will keep it much cleaner and prevent the goo from getting past the tank and into the plane. I may just put a scavenge tube on and let the exhaust pull it out and away like I did on my T-Clips.

I would ensure the screw that holds the throttle arm onto the carburetor barrel is tight.

That was a problem when I first mounted the engine, but it is on nice and tight now. The new needle assembly came and I got it installed. Its nice and snug now, no wiggle to it. Also nice that it has a spring again. Now to retune it with less than a half tank and see how it runs.