Hi have you fitted an inline fuel filter to rubber hosing as most sold these days are for motorcars and need pressure from a pump to operate. If standard copper piping have you a blockage in the piping or new taps that are greased with thick grease and blocking the flow. If you have the original pre mono carb with seperate float bowl being a 276C/1B do you have the correct throttle needle marked 6 and being 81.32 mil long as a longer needle can starve the carb. Do you tickle the float bowl to start the bike? If so if you press it for long enough does fuel flow out. Are the two small holes in the knurling on the opposite side of the float bowl top clear. Is small hole in fuel cap clear.
I did completely strip and cleaned the carb including the block ect , the bike only runs for a very short while with no time to adjust the pilot screw and does not respond to the throttle
Perhaps the flange is warped? You can test that by smearing grease all around the edges of the join to the cylinder. If the bike runs reasonably well for a short time (until the grease melts) then you know you have a warped flange and air is leaking into the cylinder. You can dress it flat using a piece of plate glass and rubbing compound, and lots of patience.
A 276AW/1BB is off a BSA B31 1946 to 1948 and may have the bowl on a 3 degree or 7 degree angle or has it got the proper M20 bowl of 1B which is no angle. If you have a 7 degree angle bowl you may find it will play up on bendy roads as too rich on some bends and too lean on other bends but should not upset the starting. If the bike is starting and then stopping real quick has it got stale fuel?
This might sound a bit daft but it's happened to mne when restoring older bikes.
A rat or mouse family makes a home in the silencer and they bring in enough bedding material to block the pipe. Successive generations bring in more material. The bike will start eventually but will not rev above idle. Worth checking...
