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How to Hitachi SU carb a 280zx (L28)


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There is no real need to change the stock fuel pump. Find a brass 3 way fitting and get 2 3/8 nipple fittings. 1 is for the fuel feed from the pump and the other is for the fuel feed to the carbs. Then find 1 1/8 fitting, this will be for the fuel return line side. You then need a fuel pressure gauge on the carb feed line. Its easy to choke down the fuel fitting installed on the return side to achieve the desired fuel pressure on the carb feed side!!!!

Yes this works, yes I am 100% certain, yes I have done this millions of times. This is how Nissan did it, although they used a piece of y pipe with a small hole drilled/stamped into the fuel return line. I think Mazda did as well :wink:

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  • 10 months later...

I removed the EFI hardware & harness from my '77 280Z, & will install a pair of SU carbs.  I will keep the stock fuel pump and will put a regulator on the line after it feeds the carbs and is returning to the tank.  I found this article in my search to know more about what the fuel pump will doing after i removed the EFI stuff.  The manual indicates that there is a relay for the pump and another one in the air flow meter (which has been removed).

So I have a few questions..

1. will the fuel pump run when engine is cranking or running with the EFI hardware & harness removed?

2. how can i pump up the fuel lines and carbs without cranking (just looking to test the pump and fill the lines)

3. where does the vent line get hooked up to return to the tank?

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The Flat Tops in the You Tube Link are Separate-Float Bowl Models from the JDM and are functionally IDENTICAL to the round tops...with the addition of an idle circuit so the jetted needles can be tapered more aggressively. They are 38mm and were available on Fairlady Z's and much later on the SSS Four-Bangers. Adjustment is via screwed jet on the bottom same as earlier carbs. So yeah, technically they ARE "Flat Top Z Carbs"...but more properly referred to as JDM 38 mm Flat-Tops.


The 46mm Flat Tops used on 260's outside the USA are similar to the ones in the USA with some stuff sealed off as it was not used there...they have an internal adjustment which is a PITA to do.

The 38mm carbs work well on L24's as a super-economy carb, and I've used them on L28's on occasion when I didn't want to down another car just for carbs.

Edited by Tony D
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I would say you need a new fuel pump, a bypass regulator is going to cost more then a low pressure fuel pump.


I'm a bit out of it so I can't recall on the EFI cars if the ECM controls the relay. I don't think it does.


You just need to make sure the relay is powered by the ignition, if you are unsure just trace the wire from the distributor and splice in and steal the signal from there. That way as long as you have spark you have fuel. 


Supply 12 volts to the pump and it will turn on as long as it's grounded. Make sure to run a switch though as if you are tapping it against a 12 volt source that will generate sparks, and sparks + gas equals a bad time.


Vent line to return the fuel tank? I don't recall any vent line for the carbs, just the vent back into the intake. 

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