Hi Andy,
Here are some thoughts.
It sounds like it can only be ignition wiring or spark plug. How do you know
the plug is firing? Do you know that another cylinder is not firing meaning
you have the wrong firing order? There are two depending on what cam you have.
I put new heads on my sons Tiger last spring and it was missing. We went
through almost all the things you went through, even to rebuilding the
carburetor. I began to think I had screwed up on setting the valves somehow.
My son finally discovered that the nuts on the spark plugs were loose
allowing the wires to rotate and fire to either the exhaust manifold or to
another wire, we are still not sure. By tightening the nuts they stayed where
they should and the miss went away. Also if you have one of the high voltage
ignition systems you should have one of the latest distributor caps with the
fins inside to increase the electrical path between cylinders. You may also
have a short in the cap.
John Logan
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