Noisy SU fuel pump.

[Hardimar]

Its a long story. Original su pump gave up the ghost. Replaced with a new style electric pump from NZ touted as the perfect modern replacement. Seemed excessively noisy and ran continually without the carb float chamber overflowing. Ran with alternative fuel supply aok. Refitted fuel line from tank no good. Checked supply pipework and found leak, fitted new fuel line from tank to pump, pump still suffering. Replaced new style pump with new su. Pumps well, switches off when carb is full but it is very noisy and i believe is struggling to keep up. My thoughts are.
1 There is a partial blockage in the fuel tank
2 As the original soldered end of the fuel feed to pump had been cut off i have fitted a flexible hose, is the length and route to pump critical, alternatively could the noise and failure be due to an air leak, no petrol is leaking from any joint. Any advice would be appreciated as we have missed 2 trips out already.
Many Thanks Mark

[bmcecosse]

Route/length not important. Do a pump test - pump 2 pints of fuel into a can and see how long that takes. You should hear the pump ticking when the engine is idling - but then it will be drowned out by the general racket when driving!

[Hardimar]

Thanks will try that tomorrow and advise on time. Mark

[Hardimar]

Removed fuel line to carb and timed, 90 seconds to pump 2 pints of fuel.

[bmcecosse]

So - no problems there then !

[oliver90owner]

Suspect air entering at the joints before the pump. This will not be such a noticeable problem with a pump 'well man of the job', but any air leaking into the pipe will clear without affecting the level to the carb. If the replacement was only just sufficient, any air leakage may well keep it running, as the air is pushed through to the carb. You would not notice any fuel leakage on the suction side of the pump because the line would empty back towards the tank so the fuel level is lower than the leak.

How have you fitted the plastic pipe? Jubilee clips are notorious for poor seals on small diameters and some pipes are not as compressible (on ID) as you may think.

A test would be to run the pump outlet through a transparent pipe to see if there are air bubbles at the outlet side.

RAB

[Hardimar]

Hi sorry for the slow response been on holiday. The fuel feed flexible has a hose tail with good compression fitting to the solid feed from tank. But taking your point on air entering prior to the pump. As the original fittings were soldered or brazed on and have been cut off i fitted a hose tail directly to the pump infeed. The original compression fitting had a flat sealing surface but the hose trail has a 60 deg standard chamfer. I thought as it was low pressure this would be sufficient but i suppose this may be the problem. I will do as you suggest with the clear pipe. Thanx Mark

[bmcecosse]

Just run the petrol into a jeely jar - you'll see any bubbles there without changing hoses......