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Hi guys, Just been messing around trying to get the fuel cap bolted back in and I heard somethind drop into the bowels of the tank. After a bit of fishing (and a lot of swearing) I retrieved it, but my question is what the hell is it? I can see how it goes back together but my curiosity has been piqued!

Intriguing! What's it made of, and what does it fit to....on which bike....1200S? I'd have said its the fuel strainer that sits on the fuel pickup pipe, but it looks the wrong shape. Where's the diagram from - I looked at the parts fiche but can't see anything that looks like it!

Pete

I think you'll find it's the anti-emissions expansion bottle, it basically takes up the change in tank pressure during temp fluctuations and prevents fumes / fuel "blowing off" to the atmosphere.
At least that's what I always thought it was ??

Or does it prevent overfilling ? I'm not sure now

Thank you for the responses guys, the expansion idea is interesting, but as its made from a hard plastic that seems unlikely. Its from a uk model '99 R1100s. It's made of black plastic with a tiny hole in the middle of it on the other side of where the metal tube enters. It's intriguing!

So I reckon it's designed to trigger your fuel filler gun as the level reaches the neck of the tank, then still allow the fuel level to drop slightly as the fuel flows into it thru' the small hole.
Thus your tank isn't ever overfilled ?

Its a 'reduction insert', apparently! Perhaps it 'opens' extra venting as the tank fills?



Pete

Looks to me like it is basically a baffle for the expansion vent. Prevents sloshing around fuel from exiting the tank via the vent pipe.

I suspect it’s a float to keep the vent above the fuel level ... bit like a snorkel, otherwise the fuel could drain/siphon out.

If you want to replace it I think I still have a complete assembly somewhere

Spot the difference between the schematic (mistake) & the picture; hint: o-ring. AND don't do what i did to correct it, lets just say it doesn't flex back to size so i discovered on weekend after accessing under tank (ecu) a 3rd time in as many months.

B

Thanks Britisherspy, but I've got it all back together again and so far it seems to be ok (after purchasing a new O-ring as I found out the same thing that bfisher did)! I was just wondering what its actual purpose was as I have no idea!