Originally Posted by carlgrover

I saw from your pictures in another post you are running muffler pressure. Pull that pressure line and let it hang. You can plug your pressure tap by putting a very short piece of fuel line tubing over it and a small screw on the other end.

The sportster engines are designed to work with atmospheric pressure only. When you run muffler pressure the high end needle is very hard to set, it will kick props at you, and also quit in flight. I had this same problem with a .65 sportster and after a lengthy heated argument about it with a technician from K&B, he got me to see the light. The very second I pulled that pressure line off the muffler, I had a totally different engine that behaved wonderfully.
carl