Spitback on XS400

I finally got my XS400 '80/'81 with electronic ignition started - newly cleaned out carbs - and its running as if its heavily choked and won't pickup.

It also spits back through the carbs - what does this indicate?!? too much fuel I suppose. Compression is good.

It idles nicely when warm but won't get going. I moved house recently and can't find the manual. Can anyone give me some pointers - eg float height on these carbs - they're plastic floats with a shoulder (see pic). Do you measure to the top of the circular bit or the top of the shoulder. What should the height be?

I think the only way to set the timing is with the bike running is this right? any tips to tune it without a strobe? except by ear?!?

Thanks in advance

Tony