fuel pump weirdness

[rhubarbray]

Ok, so I'm still going over the new-to-us Thing and learning a helluva lot. ( many thanks to this site ) We were wondering why it looked like the fuel filter has bubbles coming from the bottom hose attached to the pump and the filter never fully filled. Before you all start, YES, I'm in the process of moving it to the front! Baby steps, I'm trying to do a lot all at once. I asked my wife to watch the filter when I started the car and tell me if the filter filled. Not only did it not but there was a hell of a lot of air and a bit of fuel and the filter never filled. I'm watching it wondering where the hell the air is sucking in? So I did an experiment. Pulled the pump ( I have another story about that in a minute ) and got a clean container with some gas and some clear 1/4" hose. When I manually activated the lever on the bottom the inlet hose was clear fuel but the outlet hose was 50/50 fuel/air. I am going to out on a limb and say the pump is drawing air from either the lever on the bottom or the crimped edge? In either case I need a new pump?
Now, part 2. While I'm looking at the pump it struck me as a bit odd until I recall reading here that there's 2 pumps, 1 for a generator and 1 for an alternator. Mine has the wrong one. I have a generator but an alternator pump. I did double check and it has the short rod ( 99.5mm I think). Are the pumps putting out different pressures? Or just get the right pump and rod?

[heimlich]

Don't worry about bubbles or that it doesn't fill the filter. If you see fuel in there and you see fuel pumping it's getting it's way to the carburetor.

Different pumps and rods go together. You just have to match your style of pump to the correct rod.
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[Technut27]

Good post, I have wondered the same everytime I have the engine bay open while it's running for years. It happened litteraly about an hour ago. The car runs well so I never gave it too much thought.

[germansupplyscott]

The pump not being completely full is normal, and it's just physics. There is very little pressure in the system, like 2.5-3psi. The pressure inside the fuel system is not enough to overcome gravity. The fuel is pulled down towards the earth by gravity creating a 'bubble' just at the level of the inlet/outlet of the pump.

(if the system pressure was above atmospheric (~14.7 psi) the pump would 'inflate' with fuel and stay full)

If the filter was vertical there would not be a 'bubble', gravity - fuel trying to return to the ground - would effectively be causing the pump to stay full.
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SL

[rhubarbray]

So I just replaced the fuel pump with the correct style and corresponding rod but before that I did the same experiment. Put clear hose on the inlet/outlet ends, and manually activated the lever.......no bubbles.
So my last pump was drawing air in from somewhere. From the lever shaft, from the crimped edge of the housing,.........not sure,..... don't care.
Am slowly working my way through all the little things that have been neglected through the years. Having fun but my bikes are feeling a little ignored!