"Weight of Fuel" Problem

Hi All

I’m struggling to get my mind around this one. Any ideas welcome.

So…

As my bike (a 1995 M900) hadn’t been run for 3 years (I know, I know) I had it serviced at the local Ducati dealer before taking it away for long weekend.

On the drive from the dealers to home, it misfired a couple of times. I put it down to it “settling back in”. As I neared home however, one cylinder gave up completely. I managed to nurse it to a supermarket car park where it conked out completely and wouldn’t restart.

I called the dealer who promptly sent a man in a van to recover the bike.

He cranked the bike over (still wouldn't start) and suggested I put some more fuel in it (there was approximately half a tank of fuel in the bike at the point of breakdown).

I looked at him incredulously. Given there was half a tank in there what good would that do?

However, I pushed the bike to the nearby station and filled the tank.

Voila! Bike started. Took it for a run around the block – no problems. The engineer suggested the “weight of fuel” may have been an issue. Again, I looked at him incredulously. The bike has never exhibited this problem before and, frankly, I didn’t buy it.

Confused, I got the bike home without issue. That weekend I set off for my trip. First day went fine – in fair weather did about 200km from a full tank – no issues. Happy days.

The following day, in pouring rain, I had the same problems as before – this time with even more fuel in the tank – bike went down to one cylinder and a few moments later, none. Bike wouldn’t restart.

I was recovered to the local town where I simply filled up the tank and Voila! The bike started fine and showed no issues.

Here are my assumptions:

The problem is not electrical, given the bike works fine after refuelling.
The problem is not dirt in the fuel, given the bike works fine after refuelling?
The problem is not water ingress into the fuel, given the bike works fine after refuelling (as water is heavier than the fuel it would sit at the bottom of the tank and would be drawn into the carburettor before the fuel - regardless of the level of fuel above it in the tank).
The problem is not a vacuum in the petrol tank, given I opened the filler cap to check fuel levels on each occasion the bike has broken down.

So, what fuelling problem could be overcome by simply adding more fuel?

I’m at a loss here. Bottom line is I don’t trust the bike to get me back home each time I take it out which means it’s sitting in the garage.

All ideas welcome.

Cheers!

Col