Here Chuck let me share my notes with you maybe they can help. Click on that pic and I have written a general table to look at.

While your thinking, remember when a motor comes up on the pipe its tendency is to go lean, so always start with a fat setting with your starting length, and go through the needle first. Then move the pipe in and go through the same process with the needle.

This is where the third-channel mix is nice.

That pic I threw in is one of those copper fitting headers I've seen around. I am not sure where to get them or who makes them.

I would say give it another shot with a longer piece of coupling, and work that needle more. I think with what you said about being too short already, and running 60% nitro, you might have started too short to begin finding it, and its choked on the pipe. Drop a prop size too, get the load off the motor so its easier to tell when it jumps on the pipe.