I'm working on a dual Hitachi SU setup for my 210 (Z Therapy carbs - they are beautiful by the way but I haven't had a chance to run them yet). Anyway, I'm working on the fuel line setup now. I've got a Holley dual output fuel regulator and I'm wondering if when using this if there's any need for a fuel return line to the tank. It seems to me that using the fuel line will do 2 things. First it forces me to join the 2 dual outputs from the regulator to join them both to the return line. I dont' see the point in that - might as well have a single output regulator in that case. Also it means that the regulator has to maintain pressure not only in the short fuel lines going to the carbs but also the the entire return line back to the tank. Anyone done this before who can offer some advice? BTW at this point I am using the stock mechanical fuel pump, though when I have money somewhere down the road I'll probably switch over to an electric. Thanks for the help -

Michael

Here's a pic of my SUs just for fun. They look like nasty flat tops but they're relaly the same as round tops (notice they float bowls aren't integrated like on the crap Z flat tops). These are 510 SSS carbs, desmogged Had to get a manifold from Australia because they never had A series SU's in the US, only JDM and Oz as far as I know.

Actually the GX setup was available here in the US form Nissan Motorsports. It used the 38mm flat tops which are not smog carbs. This is a scan from one of my old Nissan Competition Parts catalogues. Doesn't really answer your question but that setup was once available here.

Wow, awesome bit of info Stephen - thanks! I hadn't heard that they were available here even through Nissan Motorsports. Hope you don't mind if I relay this info to the 1200 forum. They may find it interesting as well. I wish there were a picture showing the manifold so I could compare it to mine. If you have any more info on this please pass it along to me (off line if you like so we don't post too much off topic stuff here - I try to limit my non-z posts at least to info that is directly applicable to Z's...)

Michael

Mperdue, the second output on the regulator is for a mechanical fuel pressure gage. If you don't have one then plug it. No need for a fuel return line when using a regulator with electric pump with pressure bypass (Holley, Carter, etc.).

The regulator limits the fuel to carbs from the pump, the pump (electric) runs continously, but when regulator limits the flow the pump "bypass valve" opens and the pump "freewheels".

You will need breather lines from the bowls. If your floats don't stick, or the pressure is not to high, they will only pass vapor. BUT, they could also pass fuel. So vent the bowels to a "catch tank" to keep fuel off your exhaust.

PM me if you need photos of what I'm talking about.

Pancho

EDIT:I see you are using the positive displacement mechanical pump. This will not "freewheel" and you will need a return line to fuel tank. This is not an area I'm familiar with. It might require two regulators in series, with the first set to a higher pressure than the second. One port of the first reg would feed the 2nd reg and the second port of the 1st reg would be the return to the fuel tank.

Go electric, it's much easier.

I'll see what I can come up with. I think I have every one of those catalogs including the ones from when they were called the Datsun Competition Department.

I was goign to put a guage on a "tee" from one of the 2 lines, to get a true pressure reading of the fuel line pressure (or mabe both if I can come up with 2 gauges). But I guess if you trust that both outputs are really identical you could do as you suggest, tee both carbs off of one output and gauge the other. But putting the gauge on the real fuel line does let you see if there is a problem such as a leak or something. So probably the best solution is to tee both carbs off of one output and put the gauge on that line also. So why did I get a dual regulator?? real reason - cheap deal on ebay !

You say no need for a return with an electric, but waht about with a mechanical? IS there any sort of incompatibility between a mech pump and a regulator? Maybe if there's no return on the mech pump output it can cause excessive load or stress on the mech pump?

I would like to see the breather setup photos. I'll PM my email address. Thanks for the help -

MIchael

Mperdue, the second output on the regulator is for a mechanical fuel pressure gage. If you don't have one then plug it. No need for a fuel return line when using a regulator with electric pump with pressure bypass (Holley, Carter, etc.).

The regulator limits the fuel to carbs from the pump, the pump (electric) runs continously, but when regulator limits the flow the pump "bypass valve" opens and the pump "freewheels".

You will need breather lines from the bowls. If your floats don't stick, or the pressure is not to high, they will only pass vapor. BUT, they could also pass fuel. So vent the bowels to a "catch tank" to keep fuel off your exhaust.

PM me if you need photos of what I'm talking about.

Pancho

EDIT:I see you are using the positive displacement mechanical pump. This will not "freewheel" and you will need a return line to fuel tank. This is not an area I'm familiar with. It might require two regulators in series, with the first set to a higher pressure than the second. One port of the first reg would feed the 2nd reg and the second port of the 1st reg would be the return to the fuel tank.

Go electric, it's much easier.

Here's the other scan. This one shows the cylinder head side of the manifold.

Thanks stephen and ponchovisa. I would still be interested in seeing pictures of you catch tank in case I can find an electric pump I can afford.

michael

Michael, I'll be in my garage this weekend and will take some photos for you. Regarding the e-bay auction tou sent me to, those tubes are for "banjo" bolts (metric at that and tough to get), while the photo of your carbs shows hose nipples for the breathers.

So, not directly compatable.

I thought those connectors looked a little weird. Well I've got a tube bender so maybe I can come up with something that looks nice myself. No huge rush on the pictures. I can only work on my car for a short time on Saturdays anyway and I've got lots of wiring to straighten out anyway.

michael