The morning after the MOT, I noticed a dark patch under the bike, and assumed it was oil. It was towards the back of the bike, so I thought maybe it was the drive shaft leaking. I didn’t have time to look at it, as I was working.
During my lunch break, I took a closer look, and discovered it was fuel, not oil, but it was difficult to see where it was originating. The drip (very slow) was coming from the underside of the exhaust.
I was quite concerned that it was a cracked tank or something nasty, as there was a lot of muck and rust in the area. Looking at manuals and on VMaxForum.net showed that removing the tank is quite a job. It sits inside the frame, under the seat, and seems to require removal of the rear wheel and swingarm, and other gubbins to do much with it. Even it it were a dodgy fuel hose, that could be quite a job.
After work, I had another look, with a torch and it looked as though it might be the drain bolt, but the whole lot was so mucky it was impossible to tell, except that that area looked wet with fuel and nothing higher than that was wet.
I had a little scrub with a wire brush but that just spread the muck around, really.
A bit more degreasant and cleaning up with an old sock (pro tip, save old socks they make good rags) made things a little clearer, but it still wasn’t entirely clear where the leak was.
After leaving it for a little while, it became more apparent. The leak is from the fuel level sensor. Additionally, when cleaning it up, one of the wires to the sensor became completely detached, which probably explains why that hasn’t been working (knew about that when I bought it).
It looks likely that the problem is simply the o-ring for the sensor, and I think I can get it out by draining the tank and just unscrewing it, as I can access those bolts without removing the tank or wheel (I think).
I have the replacement o-ring, courtesy of my local Motorcycle Parts Centre. I also bought new bolts and a new drain plug washer to be sure. The leak has actually slowed or stopped since I used up some of the fuel in the tank, riding, so I’m going to wait until I’m back from Hayling Island, to avoid jeopardising that if I run into problems. I’ll also try to solder the sensor wire while I’m at it.
I was interested to find, in the Haynes manual, that they include a check on this in the 4000 mile routine service:
Check for leakage from the level sensor in the base of the tank.
If it is leaking, tighten the mounting screws (see illustration).
If leakage persists remove the sensor and replace its gasket with a
new one (See Chapter 4)