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This might be a little better...

I’ve spent most of the winter and following lockdown giving the Tenni some love. I met a fellow Tennisti in St. Louis on a trans America trip in 2018(Iwas on a triumph)and his bike put mine to shame.A mixture of shit Irish weather, bad Italian paint, ethanol and me being lazy meant it was starting to look sad. The tank was suffering from severe measles, so that was the start, and it grew from there. I had one built by MCS in brightlingsea, UK, took about 5 months, not bad considering Covid had just hit. I had various bits of plastic repainted by a pro, the Tenni paint came from Holland(rocking horse poop). I powder coated wheels, triple tree, cylinder and alternator covers and a few other bits. Taking the wheels apart was the hardest bit, all nuts and bolts had turned to cheese, so a local engineer used his box of tricks to help. Apart from a small electrical problem (see technical topics, “thirty amp fuse failure), she rides exactly the same. she just looks better. Here’s to another 20 years!

Oh ok sorry I've missed something in the previous posts. Yes you can get away with a nitrile o ring there but a Viton or FKM would be better. I use Viton/FKM wherever possible on everything now. As I mentioned the material is totally unaffected by fuel and also has better heat tolerance. Nitrile has maximum temperature threshold of 100 deg C where Viton is somewhere around twice that. There are many areas where you engine sees temps in excess of 100 deg C and this is why old head o rings for example go hard and leak. Viton seals stay flexible in these conditions. Guzzi has superseded some o rings with Viton over the years, such as the orings that go around the cylinder studs on the Daytona engines. BTW look after that tank flange adapter, they are unobtainable now. Ciao

I am referring to the flange on the fuel tap that is attached to the underside of the plastic tank that is retained by 2 allen head cap bolts. The o-ring is slid over the fuel strainer and then rests in a circular channel in the face of the flange. The channel is about 1mm deep and the o-ring protudes 1mm above the surface of the flange and is then compressed against the flat plastic of the tank when both the cap head bolts are tightened. I hope to not have to remove it again, but I got 9 spares.

Std o ring measurement is defined by ID and cross section. Ciao

GU90706116 Stein Dinse in Germany reports: Moto Guzzi O-Ring 16x1,78 Rolf

Isn't that an oxymoron?

I had to give these guys a look. I was rather hoping they had posted some images of that delicious V11 Tenni tank . . . https://mcs-engineering.co.uk/

This flange gasket almost never leaks, its some sort of hard plastic material. Its not an oring BTW but a square section and around 2mm thick. I've had them on and off many times with the same gasket used and never an issue. Check to make sure your fuel tap body isn't cracked. I had a new fuel tap body leaking in the open position and thought it was the seals. Turned out to be a hairline crack in the body itself. The crappy Nitrile seals swell so much that eventually opening and closing them with pliers with the seals half jamming cracks the body as the body is less than 1mm wall section in some places. This cracked tap was fine until I closed it and then months later refitted the tank opened the valve and its leaking. ciao

Maybe a little better...

It's probably in this thread somewhere, the reason for the 30 Amp fuse melting that is. The cause as I see it is too much resistance in the clips holding the fuse, resistance causes heat at a current squared relationship and don't forget the current is pulsing, its not a steady DC but a pulsing DC, the peak is much higher than the average. So saying my VII Sport welded a fuse into the holder but I was able to break it free and clean the socket up again. It never gave me another problem but I eventually replaced the regulator with a direct connect type. Don't re-use a fuse that has overheated toss it and replace with a new one.