Here's the problem.
I have a ROSSI 40 and it sucks the fuel fast. So in a loop or a dive it runs the line emty. I just bought this motor and this is the first time I've tried to fly it. In all other flight (level,nose up,side to side) it's good. Any thoughts would be great.

Try larger diameter lines? Unless the clunk is stuck at the front of the tank, I doubt there's anything you can do to the clunk that will help.

Anyone else have thoughts?
Dennis-

sounds like the clunk line is too short maybe?

I went out this morning to try larger lines the engine only run for 2 sec in the nose down (line emptied). I'm thinking a header tank might help, like on the choppers. Any thoughts?

I was going to suggest a header tank. That should solve the problem.

Where is the centerline of the tank in relation to the centerline of the venturi?

Could you be running overly-rich?

In the air or on the ground? On the ground the fuel will run forward and there will be no fuel available, especially if you installed thicker lines and the clunk is staying to the rear of the tank (where it's supposed to stay).

When I started running Norvel engines in my combat planes, I began having the same problem. It was frustrating at first, but then (long story short) what was actually happening was the thin chincy fuel line supplied by the tank manufacturers was sucking flat and closing off. I replaced the clunk line with the same stuff I use for external line and have not had a problem since.

If I was to use a header tank what size should i use? Also, how should I hook it up. Where should the header tank be put?

I figured out the problem. The fuel tank was sitting too low. Thanks for the help.

Try placing a straw over the the fuel line in the tank to keep it from getting stuck fwd.