What kind of pressure regulation system do these cars use?

[ntomsheck]

Hey guys, I'm almost ready to start this 260Z I've been working on for the past month. It came without the engine bolted in, so needless to say there are missing parts and bolts. I see a fuel supply line, a fuel return, and what I would guess is an EVAP line. The car seems to have an electric fuel pump in addition to the mechanical fuel pump. I imagine since there is a return line, these had some form of pressure regulation system on them. Does anyone have a diagram? Or could describe it in words? Things I'm looking for are, what the pressure should be set to, what side of the FPR the mech. pump should pull it's fuel from, etc. The car has a dual two-barrel carb upgrade also, with electronic ignition.

[Walter Moore]

The carburetor equipped cars didn't come with a pressure regulator from the factory. The return port on the fuel rail has a very small orifice to restrict the flow back to the tank and keep the pressure where it belongs.

This isn't to say that a pressure regulator is never required, just not with the factory pump(s).

[ntomsheck]

Haha well then it's missing a fuel rail. I'll rig some goofy system up with fuel line and brass fittings then to accomplish what you just stated. At least until the owner or I will buy an FPR

[oldhemi]

260Z had an electric and mechanical pump. I think that they were internally regulated somewhat to about 4 - 5 lbs - IIRC. (You dont need the e-pump to run the car) IIRC again, the FSM stated that the pressure was 4 lbs.

BUT, there was also an orifice - reducer - in the fuel return line which was the real regulator as WM says.

I removed all the fuel rails when I installed 3 webers and did not have a return line. I had to put a FPR on after the m-pump and before the carbs to stop the leaks past the floats. I dialed it to 2 or 3lbs depending on what driving I was doing. You might have to do the same if the carbs need less than the stock pressure.

Accepted installation these days is to run a back pressure regulator in the return line. Supposed to help reduce wear on the pump.

[ntomsheck]

Well the guy we're buying it from (The guy lets anyone try to get the vehicle started before they buy it, that's how I scored a 98 cherokee from him for 250 bucks), put the dual two-barrel system on it. The carbs are dirty so I can only imagine he ran it like that for at least a little while. There was a bolt jammed in each line; the return, the source, and the evap. It looks like the bolt in the return line has been in there longer (hard to tell with the general age of the parts) so I'll have to ask him how he ran the lines and how well the carbs ran in his set-up. Perhaps he just ran the mech straight off the electric with no return.

I can't find any stamping on the carbs, so I can't say whether they're weber or not - I know those are very sensitive to pressure. It doesn't look like there was a reg between the mech and the carbs - all the hoses are prefect length on that side of the pump. Thanks for your replies so far, I'll try it straight off the source line until I see the guy again. I'll keep you guys updated.

[ntomsheck]

Well the car runs and idles with the supply line hooked directly to the carb (with an inline filter, of cours). Some tuning is clearly necessary, and timing adjustment, but it's running fairly well. Thanks for all your help. See my new post in the cooling section if you're still looking to help hahaha.