Fuel pouring out the front of the carbs

[siteunseen]

That DVD method doesn't work with the newer style needle valves. You can't turn them up side down and set the distance then install them. They'll be way off. The newer needle valves are too sensitive for the weight of the floats. You have to turn them right side up and let the float hang down, blow through the fuel inlet while raising the float until it shuts off, no more air gets through. When you get there that's the .55" measurement.

Like Captain says that'll get you in the ballpark but the clear tube will get you a real idea of where the fuel levels are.

[Jeff Berk]

On 6/26/2021 at 5:45 PM, siteunseen said:

The carbed cars don't have fuel pressure regulators like the efi ones do. 

I have a regulator and assumed it was on all 260z's. I attached a fuel pressure gauge and was told to keep the fuel pressure below 4.5 psi. I guess what I'm saying is to check your pressure especially if you have an electric fuel pump and mechanical pump both running.

[Mark Maras]

4.5 psi is pushing the limit on fuel pressure for carbs. 3.5 psi is better and will supply the engine with more than enough fuel.

[siteunseen]

4 hours ago, Jeff Berk said:

I have a regulator and assumed it was on all 260z's. I attached a fuel pressure gauge and was told to keep the fuel pressure below 4.5 psi. I guess what I'm saying is to check your pressure especially if you have an electric fuel pump and mechanical pump both running.

I always forget about the 260s and my lack of knowledge about them. I don't think I've ever even seen one in the "wild". Just at ZCON and on the internet. 

[SteveJ]

4 hours ago, Jeff Berk said:

I have a regulator and assumed it was on all 260z's. I attached a fuel pressure gauge and was told to keep the fuel pressure below 4.5 psi. I guess what I'm saying is to check your pressure especially if you have an electric fuel pump and mechanical pump both running.

As @Captain Obvious has mentioned in the past the "fuel pressure regulator" in a stock 240Z or 260Z is the orifice on the return line of the fuel rail. The 280Z was the first with a stock FPR.

[siteunseen]

Is that the smaller diameter of the return or is there an actual part that could go bad and need replacing?

Thanks!

[Mark Maras]

If I remember correctly, there's a reducer (restricto) in the return line. Nothing there to go bad but it could become plugged or corroded. I believe C.O. is the one who looked into this previously.

[Captain Obvious]

Yes, there is an "on-purpose" restriction on the end of the return side of the fuel rail right where it transitions to the rubber hose (over by the fuel pump). It's a swaged down tip brazed onto the end of the return leg. 

I've got all kinds of pics of all kinds of carb stuff, and I can't find a single detailed pic of that orifice restrictor.

So, all I've got is this:

I'll take a look to see if I have any 240/260 fuel rail stuff around here. Not sure I do, but I'll look.

[siteunseen]

18 hours ago, Captain Obvious said:

Yes, there is an "on-purpose" restriction on the end of the return side of the fuel rail right where it transitions to the rubber hose (over by the fuel pump). It's a swaged down tip brazed onto the end of the return leg. 

I've got all kinds of pics of all kinds of carb stuff, and I can't find a single detailed pic of that orifice restrictor.

So, all I've got is this:

I'll take a look to see if I have any 240/260 fuel rail stuff around here. Not sure I do, but I'll look.

You pointed it out, I found it then. Now I understand. Thanks.

 

[siteunseen]

[Captain Obvious]

Yup! There it is! Thanks for the pics!

So that little hole partially blocking the return line of the rail is what provides the fuel pressure to the carbs. If that return line wasn't necked down like that, the pressure in the rail would be pretty much zero and the carbs wouldn't get any fuel. That orifice provides the restriction which generates the pressure in the rail.

[Zed Head]

I wonder how much pressure the original electric pumps for the carb'ed cars generated.  The system started with the mechanical pump that relieves pressure at the pump itself through internal valving.  They hit a pressure and just don't push anymore.  What did Nissan specify for the pressure of the factory electric pump?