Pete, the cold start obviously require more fuel, I run the larger type 504 chamber, I think yours is a 303. Both of these are designed to cope with Alcohol fuel, and have a high flow rate, so can easily be flooded. I find mine starts best from cold just before the point of flooding, if the fuel exits the bleed holes at the top of the chamber, this can cause problems starting.
The technique I use, is to listen for the change in note as the fuel fills the chamber when operating the tickler, I can then estimate the point just before it flood. (Not much help though if surrounded by noise ) If it does flood, I hold the throttle wide open, and give it a few kicks using the valve lifter to clear it out, if this fails, a change of plug usually dose the trick. (NEVER go out without a spare clean plug)
Obviously you are adept at starting big singles. This is my procedure , I leave the air correction valve fully open, as in the run position, kick it over a couple of times using the valve lifter, then bring it up on compression, and just ease it over TDC, set the ignition at the point, just enough to eliminate kick back, as over retarding weakens the spark. Then kick it as if I intend it to start.
They always run rich at the initial start, but this soon clears. The pilot adjuster needs to be set a tad on the rich side, to obtain a sharp throttle response.

I have converted my float chamber to use a Weber needle / valve and seat. The original valve seat being just the alloy top cover, the needle also being alloy, obviously to reduce weight. these can wear quite quickly, which I put down to vibration. This modification solves the flooding issues when the engine is running.
I noticed from your previous post, that your fuel pipe inlet banjo is the 180 degree type. It should be a 90 degree 14/250, this allows both fuel pipes to be rubber clipped to the frame tubes either side of the battery, also helping to prevent vibration of the chamber.