jmminbmx, I've been through the whole fuel tap thing recently, see thread below.
http://www.ukmonster.co.uk/monster/s...ad.php?t=58052
The vacuum tap is easily checked. You can blow through it from the inlet side and it should'nt pass any wind
if it does then it is prob shot and will allow petrol to reach the carbs when the engine is not running. If it seems ok and not passing, you can also check that it's working by disconnecting the outlet fuel line, connecting the inlet fuel line from the tank/filter, connecting the vacuum pipe to the manifold and turning over the engine (pull the plugs out first). It should spurt petrol from the outlet spout with each revolution of the engine (put a rag under it or you'll have petrol spurting over the engine).
In my case, the float valve in the carb was also sticking open and it filled the front cylinder and crankcase.
I fitted a new non ducati vacuum tap which cost around £6 with a simple home made bracket. I also fitted an in-line fuel tap between the filter and the vacuum tap. just as a belt and braces.