Personally I would have the carbs apart and see what's going on in there- there's obviously something amiss if draining and then them refilling is disturbing something enough for it to start afterwards. I know it's a bit of a pain in the ass but hey it's Winter, the weathers' rubbish and think of it as 'bonding time'.
For what it's worth here's some of my recent findings from over eighteen years ownership of a 1997 900:
Firstly and possibly the most important thing is that the battery is not only good but has a healthy charge- turning the motor over on the starter while it is trying to huff and puff into life runs a very real risk of damaging the sprag clutch.
Next is to make sure all the *ground (earth) connections are as good as they can be*-
The wiring here was marginal to begin with but over the years is likely to have built up a degree of corrosion causing some resistance. You can check this easily using a multi meter set to the Ohm (Ω) range and measuring the resistance along each individual ground cable- the higher the number equals more resistance stopping the cable from doing it's job which is bad.
Coupled to that Ducati also chose to use a lot of brass terminals for this wiring which isn't quite such a good conductor as copper would have been adding slightly to the issue.
Now we can get onto the fuel pipes and pumps, firstly there are two vacuum pipes that need to be in good order. They run from each of the inlet manifolds with one going to the vacuum fuel tap located under the fuel tank- this isn't rebuildable and costs about £30 (if I remember correctly) from Moto Rapido. The other goes to the Mikuni vacuum fuel pump fixed to the frame which is rebuildable with a kit from Allens Performance for about £20.
Any other weaknesses in the fuel lines will show themselves more readily by leaking fuel.
The problem I encountered only showed itself on very hot days and typically when filtering through slow traffic so with either (or both) the vacuum tap or the vacuum pump not working as well as it should it caused the fuel system to vapour lock as the float bowls were not filled fast enough- compounded by the engine running so hot helping to evaporate the already in short supply fuel.
I'm only down the road too, so likewise shout if I can help further- if only it was better weather, there'd be a Monster run out there eh Nasher?
Fuel pipes:
Vacuum fuel tap:
Vacuum fuel pump insides:
Rebuilt:
I also replaced the other fuels pipes etc.
**A poor ground (earth) connection can also be the reason why on older bikes some headlights are not as bright as others (not to be confused with the poor beam pattern of the standard Bosch unit). Just for fun try this little test:
You'll need a length of wire long enough to go from the negative terminal of the battery to the headlight. Fix a M6 ring terminal on one end and a small crocodile clip on the other. Take the light unit from the bowl and make sure you are able to get the crocodile clip onto the ground (should be the black one) of the three terminals (don't clip it on yet though) .... turn the light on and note it's brightness, now attach the crocodile clip to the ground terminal and (possibly) be amazed how it becomes brighter!!
If it does then that is the result of corrosion and thus resistance of the light circuit going to ground.
**Disclaimer- I am not, will not and can not be held responsible for any blown bulbs, fuses or any other part, person or thing during this experiment
