Just to keep everyone apprised of how this comes out.

Today I experimented with the intermittent power supply to see if it fires at the application of power or the removal of power it does. From now on I am going to be sure my arm is clear of the prop arc before operating the kill switch.

Then I removed the kill switch thinking that was the only component I had not touched and it still exhibited the same problem.

Here is what I now know - the mechanical linkage is correct and moving the requistie 28 degrees CW, the keyways are all pristine, the battery has been replaced, the ignition has been overhauled and the kill switch has been eliminated. Hmmmmm.

With nothing left to do I opened the H needle 1/2 turn (Ouch) and the backfiring went away. Now the idle is fine but I lose about 200 RPM after a few seconds at WOT where it settles down and still seems a little rough. I now have to agree with Kimhoff's theory since I have eliminated the ignition and opening the H fuel flow up definitely made a positive difference.

I will let you know how this gets resolved.

Thanks for the input Bob