Hi Norm,
If it was me I'd be giving up on this one. Usually unless the mower has specific sentimental value to me or I am extremely bored I will strip it down and use it for parts at this point (I get the impression you get driven nuts until you solve the problem though). I'm sure you know this already but over time I have found the plastic air cleaner housing warps and these carbies rely VERY heavily on a good tight seal here. I usually find chucking a 2nd carb gasket on fixes most hard to start issues on Quantums as it builds up the thickness and seals all warped areas.
Just my thought; I really have nothing of value to add past this point.
Pete
