hi john , i had similar thing with my leader this weekend gone , it ran the first time i started it but then i changed one of the exhaust downpipes and next time i tried starting it i couldnt get it going .
did have a bit of fuel down on the floor and although plugs were wet at tmes and still sparking it wouldnt go .
i left plugs out overnight then tried again the next day , this time with the choke on it would try to fire on one cylinder but not two , and i could kick it in succession and get it to fire but not run .
eventually it did go and then on both cylinders .
the downpipe wasnt sealing quite enough and through that i noted a fair amount of fuel mix running out of the exhaust port and down to the floor .
i had obviously flooded the engine to the extent of having the crankcase full of fuel on one side .
gong back to when i first got the bike out of storage i had a fair bit of fuel out of the carb and on to the floor , which was caused by the float needle staying open .
there is a little article i copied and attached which says a few things about the float etc on amal carbs .
i think you can raise the level using a shim washer kit from amal but if you need to lower it i am not sure if the new stayup float kit is and adjustable tang on the float to allow this , although the guy in the article machined a needle seat down a bit so he could lower his float level that way , and then if reqd adjust with shim kit .
not sure if the new amal needle seat face is shorter than the originals , so you can facilitate float level changes .
looks like if you have a brass float you can add a blob of solder to the tang and file it to suit and set float level , but would maybe need to be quick soldering as you dont want to unsolder any of the float joints .
i did have a brass and a nylon needle and it looked like one produced a different float height to the other when i was swapping about parts .
the original needle was the nylon one and the brass is a later viton tipped type , so perhaps theres a difference between parts .
i dont know the float level for the monobloc off my head .
i had a flooding issue on my cafe racer ariel but that uses a concentric carb and it was the float level that was the culprit , but i could adjust the float on that one and set the level as i wanted .
ian http://www.whfolk.co.uk/REOCHUMBER/Arti ... nobloc.htm