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What is needed to convert L28 to Carbs?


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I have a stock 78 280z and have been searching and couldn't find the information I needed. I found a set of used SU's off of a early 240 on craigslist and have been wanting to carb my 280 since I bought it. I was just wondering if it was a simple bolt on or what all is needed to convert it? If anyone could give me some info that'd be great, thanks in advance!

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You could always install a stock fuel pump and rely on the stock rail to regulate the pressure.  You might have to drill and tap the head to get it to fit, but it's an option. 

 

As far as wiring,

remove the EFI harness

provide the coil/distributor with 12v (if part of EFI harness, otherwise leave stock)

Run new temp sensor wire to the appropriate connector (if part of EFI harness, otherwise leave stock)

Run new oil pressure sensor wire to appropriate connector (if part of EFI harness, otherwise leave stock)

 

I'm fairly sure alternator is part of chassis wiring, but can't remember if the Coil, temp and oil sensors are part of EFI harness or not. 

 

Download the FSM and look at the diagrams to understand the circuits, and where the relevant connectors are on the vehicle. 

 

Hope that helps.

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I did the same swap - it's very easy.  Roughly, it goes like this.

 

The FI harness separates from everything else very cleanly, so pull it, the ECU and anything connected to it including the stock ignition module under the pass. side dash.  The only thing I saved was the FP relay which just took understanding the schematic.  There are two wires to the FP relay that are part of the FI harness that connect to the AFM as a deadman.  Leave those two wires in place (both green like most of the FI harness) and do one of two things: Connect to an oil pressure switch to run the pump only when there's oil pressure (safe way in case of crash), or just tie them together until you decide how you want to deal with them (what I am doing).  I unwrapped the entire FI harness, stripped out the unwanted garbage (almost all of it) then re-wrapped and routed what was left.

 

I then bought a bypass regulator ($80) and, using the stock hardlines in the engine bay, plumbed the inlet of the reg to the feed from the stock pump. Plump the bypass from the reg to the return line.  Then, reg output goes to the carbs, deadhead.  There are other options here, I haven't found one to be better than another.  The stock carb rail has an orifice in it to regulate pressure, but I didn't want t trust that against the FI pump.

 

Next you need to deal with ignition.  I started with a stock points dist. that had been converted to an optical trigger and an Allison unit (now Crane).  I recently swapped to a zx dist (with the E12-92 module - which works fine, regardless of what some folks say).  The wiring needed is already at the Dist - mainly 12v+keyed.  Exactly what is needed will depend on what dist you use.  Ignition, in general, is fairly easy.  You need 12v to charge the coil and some control to manage firing the coil.  Look up any of the distributor swap writeups and you'll be fine.

 

The temp sensor line is already there coming from the chassis harness on the left fender.

Oil Pressure is already there on the right fender.

 

The job is not a difficult one, but you do need to be able to read, trace and understand a wiring schematic to do it cleanly.

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Ah - Forgot that i was starting with the wrong motor in my swap.  I had an FI chassis complete, but no motor, sourced the carb'd motor and mod'd from there.  

 

Thanks for the catch.

 

And i don't know about the '78, but my '77 had the enormous transistorized box that lived by the fuse box inside.  If you're going through the trouble, why not ditch the crappy setup for a better one?

Edited by SlowRob
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  • 2 weeks later...

I did this swap on my 77' about 2 months ago. I used a 3-4 psi off the shelf pump from my local orileys. I wired it up using a simple relay. I have the 12v signal wire going to the 6 pin connector that the efi harness used under the steering column. I also wired in a Ford inertia switch just in case something happens or I was to get hit. I did not use a pressure regulator as I had the fuel rails to go with my carbs. The factory rail has the restrictor built in. 

 

I removed the EFI harness, very simple. Its 100% separate from any other harness and wont hurt anything once removed. all of your gauges are in a separate harness so they will all still work. as for your ignition system, im not 100% sure on. I used a 1980 280zx e12 distributor on my setup and I was able to delete the huge ign module thats above the fuse panel in the passenger side kick panel.

 

I think all you should have to do is run a wire from the NEG side of the coil to the blue wire in the 6pin connector under the column. The FSM would tell you for sure.   

Edited by ZXT_bean
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