Tinkerer, the float was set too lean. On another note, just did a compression test, and I have no compression on either side......back to the drawing board...lol
No compression? Thought you said 'kicked like a mule'? Is this your first Triumph or a bike that you've ridden and are familiar with what a Triumphs compression when kicking through feels like?
Adjust valve clearances, recently rebuilt engine with no compression on both cylinders unusual and the first go to should always be the easiest. I would imagine you'd hear or see cylinder head gasket leak.
I see you said valve clearances were to spec but was this check done since the 'no start' scenario? Any chance you retightened head bolts, cylinder stud nuts, rocker boxes without resetting valves? If you still have valve clearance, then listen at carb inlet and then exhaust outlet while kicking engine through or easier while doing static comp check. A leak at either valve location will indicate poor valve seating and loss of compression and hard or no starting.
Until told otherwise, my money is on valve clearances. Mark R.