Is this component also meant to act as a vacuum fuel switch, in place of a mechanical fuel tap, via its internal one-way valves?

I've had the carb leaking intermittently but now to the point where I've got the fuel line from the bottom of the tank pinched off (just by the filter). I had assumed this was a carb float valve issue but maybe the pump is involved as well or instead of...?

thanks

The pump is just that and not a fuel ''switch''. Check your fuel tank vent hose to make sure its not blocked and allowing pressure to build when parked and put extra pressure on the carbs needle and seat (which should be in perfect clean condition), proper float level is very important too. 

Later ones had a mechanical on/off tap fitted, could have been to aid tank removal or as a shut off. 

I believe that some of the newest Sherco's with the rear mounted fuel tanks had some extra " plumbing "  .  I think that the fuel feed line to the carb had a  " T " fitting and the third hose went back into the fuel tank.  Hopefully someone else remembers better than I do.  Good luck.

This is covered in        Stalling on Downhill         in the Sherco forum  April 5, 2013

The fuel lines on the rear tankers go hard and split. which causes all sorts of unusual problems, including fuel APPEARING to leak out from places whereas in fact it is coming from elsewhere.  It can also make the engine play up, perhaps intermittently or under certain conditions.  The fuel lines can need replacing in 18 months.  

I've got a Yamaha TT250R from 2005 that's fine and has never had carb, fuel line, electrical or any other problems! And I've probably done more off road on it as well!

Why are these bikes so crap!? 

Generally most modern trials bikes are pretty reliable . The 2010-'15 sherco's did not have the best fuel tank system for reliability and were/are prone to problems...art least you did not get one of the ones with the  formula hydraulics    Hope you get her sorted soon

7 hours ago, v1nn1e said:

I've got a Yamaha TT250R from 2005 that's fine and has never had carb, fuel line, electrical or any other problems! And I've probably done more off road on it as well!

Why are these bikes so crap!? 

It is basic plumbing. Crap goes downhill great, uphill poorly.

 

So, to hopefully close the sorry saga of my 2011 250, I dismantled the carb and discovered that it had a 250 float valve fitted, instead of the original 200 size. Both floats were in perfect condition.

I notice that the Splatshop article for the 2011 model mentions upping it to 250, albeit on the 290/VHST carb. Anyway, I replaced with a new 200 size and it all seems to be working, no leaks.

Note that it is very easy to get the throttle cable dislocated from it's seating on the top of the carb, when re-installing the slide mechanism, causing the throttle to be held partially open.