I just inherited a 1974 260 Z. It's been sitting for 10 years. I am trying to get it running again. When I turn on the ignition and the fuel pump starts fuel comes gushing out of the open port on the rear carburetor. I don't even know what hose should be attached to it or why fuel is spraying out. Any help would be greatly appreciated. Please see picture for open port on the right-hand side of the carburetor. Thank you very much.

Your going to need to set your floats and clean your needle and seat the problem is that it isn't shutting off the incoming fuel grab a 1/2 inch drill bit as your measurement between the float and lid and bend the float until it touches the drill bit

And that line gets a hose on it and goes to your air cleaner

You can also find a lot of good info in the fsm it's hard to find but search for it and download it get the 72 240z fsm and the 74 260z fsm as those carbs are most likely 72

Congratulations on being a new Z owner. Round tops, so not quite stock. This sounds like a minor problem. You need to study the basics of the SU carbs, the FSM (factory service manual) is very good for this, and there are some excellent tech articles on this site. Chilton is also OK. Also ZTherapy "Just SU's" video for more in-depth stuff. 

 

The open port is a vent. If fuel gets too high in the float bowl, it comes out the vent. Normally the vents have hoses to the air cleaner, so any fumes are inhaled by the engine (I prefer to have the hoses lead to a container or the ground so any overflow can't drain out on a hot manifold, just my opinion though).

 

I'd guess it's either a worn out float bowl valve (kits are available that include gaskets for the float bowl), gunk stuck in the valve, or a leaking or badly adjusted float.

 

Maybe a good idea to pull the drain plug at the gas tank, and drain the old gas into a container. See if any rust or dirt comes out. You could put in some clean gas, put a hose on the fuel rail leading to a container , and crank it for 15 seconds to clean some dirt out of the fuel lines, and install a new fuel filter, before cleaning the valves or installing new ones, etc. The rubber tip on the valve needs to come to a sharp conical point, otherwise it's toast. Also check the filters in in banjo bolts that the fuel hoses go to; put new ones, or clean them with carb cleaner. I tossed mine, seems ok without them.

 

Be careful and good luck.

You can get the service manuals here:

 

http://www.xenons30.com/reference.html

 

The float valve could simply be held open due to the flaot being "glued" down from old fuel that dried out while the car was sitting. Start by opening the float bowls and cleaning all the old fuel out. Check the float valves for wear and adjustment while it is apart.

Take the float bowl lids off.

Remove the needles and seats that screw into the lid and flush them out with carb cleaner. Reinstall them in the lid with the float and blow into the fuel inlet tube while moving the float up toward the lid. You will feel resistance to your breath when the needle closes.

 

Resist the urge to start readjusting the floats because there is nothing that happened to change float levels during the engine's down time. 

 

Also more than about 3 1/2# of fuel pressure can overpower those needles and seats causing what you are seeing also. What are you running for fuel pump?

 

We have a 4 hour fun filled action packed dvd JUST SUs that'll tell you more than you ever wanted to know about your carbs.

Thank you all for your time and great advice. You have me loots of work .

what type of fuel pump foats etc...???