740gl main fuel pump

My main fuel pumb is making a strange noise, almost like it has bubbles or air in the system, any one any ideas, is the pump faulty, or is perhapes the fault with the intank pump failing to suply fuel. Engine does seem to be a bit flat, and I have read somewhere in this forum that this could be the fault of a pump not working. I have tried the listening at tank top to hear pump. but to much going on with other one.

Thanks for that Colin. will need to check it out. didnt want to go into tank though.it looks a bit daunting.

Found my way in to the tank. only problem is how to test if it is working. anyone any ideas. would be grateful.

Thanks again Colin. That link looks very informative. I will check all your info out and hope that helps. Regards. Stan

Problem solved. Fitted new pre pump (2 hours max) and main pump is now quiet, and I can certainly hear pre pump run now, something I had not heard before. Thanks again to Colin and his amasing link. Regards Stan