Marc

Why not do some research and let us have the findings.

If you start with a simple tank and 6mm tubing, and make sure the 180 will reach full power. Then try introducing say 1 ft length of thinner tube to the suction side. If you restrict the flow a lot you will see a stream of bubbles from the pump cavitating and the engine will not reach full power. You should find that the length of the thinner pipe will make a difference as well. If you want to do a very simple check you can fit a valve and gradually shut it with the engine at fill power.

You could repeat the exercise on the outflow side of the pump, which you will find is not as critical as the suction side. (I think Wren run 3mm pipe on the outflow of their 160). The air vent will not have a big impact either.

John