I've been driving my newly acquired 75 280Z for a week now at just about 200 miles logged. When the car was shipped to me I got it with a full tank which I thought was both odd and nice of the PO. At half a tank I got some sputtering like it was out of fuel so I thought the PO didn't fill it up and instead had a bad gauge and I was on empty, so I filled up, the gauge correct, btw. Again at half a tank (and now lower) I'm getting the sputtering again AND a buzzing sound from the rear of the car. I changed the fuel filter and the fuel that came from the IN side was a nice brownish tint. After changing the filter the buzz was gone and I noticed an instant improvement in throttle and idle. I figured all was well until I was almost home and got another sputter and the buzz noise returned. I climbed under the car while it was running and looked for the noise and found the return fuel line from the tank was actually creating the noise and vibrating slightly and not from the pump directly as I had assumed it was. It was almost like the was air combining with the fuel inside the hose.

I assume it's time to drop and clean the tank? Broken pickup as someone else suggested? Any ideas?

Thanks in advance.

Some times the brazing on the tank fittings cracks and the inlet/outlet pipes can move/rotate along with a leak.

Maybe no / bad fuel damper .

Maybe no / bad fuel damper .

Not sure of the condition, but the damper is in place. I would think that far along the fuel line the damper would be a non issue.

My guess would be a broken or rusted fuel pickup. It happened to my first Z, which was also a '75. I would get to a half tank, and then I would be out of fuel. I don't recall having heard buzzing sounds, though.

Fuel damper is supposed to keep vibrations from happening so if have vibrations in return line I would replace the damper first.