Regarding fuel filter, this should be changed quite regularly - think of it being an air filter, but for petrol.
Also, check the tightness of the fuel pipe in and out of the filter. That’s where mine came loose. Quite common on Griso’s
Thanks Brian. The bike has just over 4000 miles on it so hopefully it will last a little longer.
Thanks again for the tip.
From what I can see it’s jubilee clips so I’ll definitely check them.
Hi Brian, I’ve just taken the tank off and there’s an alarming amount of crud in it.
Might be an idea changing the filter more often than I thought.
I’ll have to check the recommended replacement interval.
It gets worse!
When I poured out the dregs, look what was there.
I’m guessing the bottom layer is ethanol and impurities. This is on a bike with only 4300 miles, with the last two fills (my ownership) being E5. Plus, as it’s a Mahle filter and jubilee clips, the tank has been open at least once before.
As you probably know the ethanol is hydroscopic and grabs water from the air above the fuel, some of which settles out as temp changes. Add the water that tumbles in from the filler well when the drain blocks = a lot of H20 in the fuel and that is why there are rusty steel components around the pump and filter.
Apparently the spring in the fuel pump non-return valve can rust to the point of failure - but i don’t know if it is available separately sorry 
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I just find it astounding that it could be so bad so quickly!
I didn’t know there was a non-return valve but it makes sense they can stick/ fail.
Depending on the angle of the tank, mine leaked out of the red connector; not knowing about the valve, I thought it was meant to! 
Can the filler drains be checked/ unblocked by blowing up the two pipes at the rear of the tank?
Edit to say the left hand drain is blocked. Does anyone know a way to clear them?
Another edit to say it was blocked at the fitting itself, where the pipe pushes on. I cleared it using small drill bits and blowing with compressed air.
Ok another daft question; where should the two pipes from the filler cap go? Mine connect together at a T piece then go a connection behind the rear brake reservoir, near the shaft drive. Which seems odd to me as aren’t they meant to take water away from the cap?
Thanks.
The two drain pipes, go to the tee piece (one for petrol, one for water).
Normally the water one blocks only and it is at the point where the nipple connects to the tank, if you have tank off you can hand (fingers) drill the crud out, making the hole bigger helps.
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Thanks Brian. That’s exactly what I did.
Where should the pipe go after the T coupling?
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The pipe goes down and pokes out below the rhs footrest hanger on my sport
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Thanks Brian. That’s much more like I expected.
Plus, after I posted my last message, I found an unused pipe that appears to go exactly where you said.
Which lead me to my next question, if I swop the pipe over, what should go on to the breather behind the brake reservoir?
That sounds like the gearbox breather hose, if so that runs up along the top frame rail.
Don’t know if you have tried looking through Griso ghetto - good source of info
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Yes that’s probably it, just totally missing on mine.
I thought this bike was immaculate and well cared for when I bought it but now I’m beginning to think otherwise!
Hi again, I’ve fitted the replacement thermistor but still no light when I plugged in the pump unit to test it before refitting the tank. Do you know if there’s a way to check the light to sensor wiring?
I’ve 11v showing at the socket (white wire) with the blue going to earth.
Thanks.
Just a note for anyone else doing this fix.
After washing my bike I left it ticking over for a few minutes to dry out and the low fuel light came on. I added a little more petrol and it went off correctly.
Maybe the bike has to self-check or recalibrate or similar before it works.
Another quick update.
I was out on the bike earlier and the low fuel light came on at 98 miles, a bit less than I’d hoped, but the remaining miles slowly counted UP to 60 miles, so I guess somewhere around the correct tank range.
I filled up with 12L and the light went out after a few minutes.
After only 20 miles, the light came back on and over the next 60 miles it went up to 80 miles remaining!
I’m now thinking it’s the warm weather affecting things (23-25C) plus a hot engine, or the sensor is the wrong range for the Griso, or maybe my bike is inhabited by its own Italian gremlin?
I’ll let it cool fully overnight and see what it’s saying in the morning. 
I went for a ride on my 1200 Griso after the winter break the other day. I had previously filled the tank up to the brim for the storage months but 25 miles into my ride the fuel low warning light came on…topped it back up 13.53 ltrs of fuel and it went out. That meant 16.4 ltrs (tank capacity) less 13.53 ltrs there was 2.87 ltrs or 0.63 galls in reserve. Maybe those Italian pixies had been at my fuel over the winter months. I’m beginning to question if I did in fact fill up the tank 