air bubbles coming out of fuel line??

[Sonic]

I have had this problem since i bought my 73, 240z. When I have the engine running i can see tiny bubbles coming out of the base of my clear stock fuel filter. Under a load, the fuel level will fall below the filter 'sump' and the pump will suck air. I have replaced all of the rubber lines, filters, fuel pump, and checked the lines for damage. Still not resolved! The only way I keep my car from dying going up hills or when under load for long periods, is a temparery electric pump.

What could be causing this?

[CoastGuardZ]

Are your fuel lines the proper size?

They're not too big are they?

Is the fuel pump new or just another one that was lying around?

Does the car also blow black smoke out the pipe under load?

I guess it might could be a carb problem.

What size carbs are you running?

This is a good one to keep bumped up on the list. Maybe someone has heard of this before?

Good luck

Nate

[2ManyZs]

How long has the mechanical fuel pump been on the car?

I'm thinking a lot of it might have to do with the mechanical fuel pump being not up to par, that is why it not keeping up with the engine under load. If the diaphram in the pump is going bad, it will suck air easily, yet not draw fuel. The worse it gets, the less fuel it will draw into the lines as it is a lot easier to draw air than it is liquid.

Since you have a 73 I'm kinda surprised it didn't have an electric pump on it already as they were installed as a recall to cure the fuel vapor lock that was a problem with the 73 and 74 with the flat top carbs.

Another thing that could be a problem is the pickup in the tank, it could be partially blocked by crud from the bottom of the tank and is not allowing sufficient fuel flow to the mechanical pump. You could take the line off at the tank and blow a little air into it to see if it clears it, then reconnect it all and see if it makes a difference. Be sure to remove the gas cap to let out any pressure before you blow out the lines....You could also blow the line backwards form the fuel filter inlet to see if the line itself might be partially blocked..

All in all, leaving the electric pump on would be a good idea, especially if you are still running the falt tops...

[Sonic]

Well I am running rebuilt (by ztherapy) 1970 su carbs. When I first got the car, the electric pump wasn't wired up, so I just took it off and ran a line directly to the tank. I was having the same problem before so I thought that if I remopved the electric pump that it would solve it. Than I got a new pump, same problem, than I blew out the lines, with an air compressor. still, nothing improved. So I just put the electric pump back on and wired it up. it runs great and the fuel filter (in the stock location) fills up all the way, But I still see bubbles!!!! The thing is I don't want to depend on an electric pump! shouln't a 73 240z mechanical pump be sufficient enough for round tops and a good radiator and cooling system?

The car origonally had a frigi king a/c system, that I removed, if that helps any? I also removed all emission control. did the frigi king intall people, that hacked up my car to install the a/c, do anything to the fuel lines by chance??

sorry about the long message!

anybody else have this problem?