No fuel flow into carburettor

[zincnlead]

I am new to this forum, and wonder if anyone can help me with a problem with my 280S. For the second time in a year it has stopped dead, with no fuel flowing into the carby. First time, I replaced the float valve and the float itself, and all was well. This time same thing, but it seems fuel is not getting into the carby itself. Has anyone had a similar problem? I think it should be a simple fix...hopefully!

[another sad 280s]

my advice would be to check that the fuel pump is working. disconnect the fuel hose on the carb, get somebody to turn the ignition over. this should result in fuel being pumped out. if not then check you're getting fuel to the pump by disconnecting the inlet hose. this should at least give you a better indication of whats happening

[oscar]

A couple more things to check.  You might find that after undoing the line into the carb that fuel flows out that line whilst someone else is cranking the engine over.  But put your thumb over the end of the line to see if there's any pressure behind that flow (a fuel pressure gauge would be best if you've got one).  If there's no pressure your fuel return pressure valve may be cactus as well.  (pic below). NB: Make sure the vacuum connection is connected to manifold vacuum.    But before you go replacing it, do this same test by testing the pressure before this return valve so you get a reading or feel the pressure coming straight from the pump, see if there's much difference.

If there's good pressure from the pump but not after the fuel return pressure valve, you can place a restriction in the return line like a screw thread with head cut off.  Small enough to partially block the flow back to the tank without being able to travel up the steel line.



Two more things to check are filters.  Maybe you should do these first but there's a filter into the carb.  It's situated directly where the fuel line goes into the carb.   Remove that and give it clean. (1st pic)
The next filter is situated in the fuel pump.  Remove the center screw of the fuel pump's cover (2nd pic), pull the cover off and there should be a cup shaped gauze filter inside.  This one's a newish pump, replaced before I got the car so I haven't checked this one but give the gauze filter a clean.
Once that's all done, hopefully it was just some gunk in the filters that caused flow issues rather than having to replace the pump. If that's all it was, it might be beneficial to put a disposable filter in the supply line to the pump (3rd pic).

[zincnlead]

Thanks to all for the replies.  Luckily the solution was pretty simple in the end. The small float valve sits in a brass tube, and it seems that over time (30 years?) this brass tube works its way out of its seat, upwards. When it gets to a certain point, the tube blocks off the fuel coming into the carby. I was able to simply take out the float valve and press the brass tube down into its seat with my thumb.  I was advised not to tap it hard as you can bust the aluminum casting at the bottom.

Re-assembled, the car started perfectly and acceleration is smoother than before (no flat spot) and idling is smoother too. 
 

[oscar]

Yeah I was going to suggest that next   
Nah I thought you had the float side of things covered and I didn't really expect that to be an issue.  I really thought you might be up for a new pump.  It's better news than I was expecting, well done.

[zincnlead]

Thanks Oscar!