Hi Robert

Still sounds like a lack of pressure. When I had a problem like this I still had a good blast of air out of the tank. With insufficient pressure you will idle and the motor will pick up but at some point the engine cannot get enough fuel then run lean and start to detonate, which is that banging sound. I dont know if you have cleaned or replaced the check valve but I would try that first, dont rely on the burst of air to ensure that you have pressure, make sure that your check is in good shape.

Beyond that ensure that your regulator is flush, if it is dont touch it yet the motor should run correctly out of the box. THe condition sounds lean, make sure that your high speed needle is sufficiently rich, all of my L's run at ~1.5 turns out on the high end, set it at 2 turns and go from there. The low end should also be 1.5 turns out to start with. Make sure that all your lines are pin hole free and that your tank does not leak.

Check the valves, 0.002" (.051mm) is the place they should be. Make sure the valve cover is seated on the gasket properly, if it leaks you will get a lean run condition. A good way to make sure it seats and something I do to all my YS motors is to "true" the valve cover on a peice of glass with fine sandpaper. Essentially what you do is to sand the sealing surface on the glass until all the black oxide coating is removed, this gives a nice polished surface for the gasket to seal against.

I dont like removing the regulator until all other areas have been looked at as it is too easy to get some crud in there when you take it apart then you have real problems

Anyways try some of that and see what happens.

Sorry I dont remember speaking to you at the WC's it is still a blur for the most part Send me a picture of yourself and I might remember, I am better with faces