Bubbles are not normal and I know where they are coming form if you are using either the old school replacement electric solenoid changeovers or the old brass tap fitting., those points.


usually if the diaphragm in the pump lets go you will also pump the fuel into the engine oil and it wont hold or make much pressure

4psi is nominal as already mentioned But you should also test it with the engine running. occasionally they will pump harder at higher RPMS use your same test jig but before you hook it up warm up the engine then restart it with the line off of the carby blocked completely and see what you come up with.

while the engine is running once you get to peak pressure if you have any needle shake on the pressure gauge your pump needs cleaning/rebuilding.

the seal on the filter bowl occasionally goes brittle and leaks but is generally good once replaced for 10 or 12 cleanings of the bowl.

the water traps work on the simple principal that fuel is lighter than and imiscable in water so if you get a flow of liquid moving slowly enough across a bowl any water will simply fall out of the fuel to the bottom and clear fuel can drain off of the top.


cheers.