How-To: N/A 280zx S.U. Carb (Hitachi) conversion

[Ryoskatekov]

There has been a couple of 280Z S.U. carb article but I have yet to see a 280zx one so here it is. 
 
Before anything: This conversion is relatively easy. It could be done without any power tools IF everything came out un-siezed (which it won't... Trust me) . Hitachi S.U. is a wonderful carburetor that gives you great fun and induction noise with reliability and minimal re-tuning. It is also very affordable if you rebuild it yourself. However It is still a carburetor so I do not recommend doing it in states where summer and-or winter has temperture extremes.    Oh and not to mention, DO IT AT YOUR OWN RISK 

 

*NOTE* This write up is written ASSUMING you have a GOOD pair of S.U carbs. So If you need a write up on Rebuilding S.U carbs, There are plenty out there. GOOGLE IT!

Things you need:  ( I will keep it short and simple here for easier read. will put more detail in the actual step by step part) 

-The mechanical
 - 79~83 N/A 280zx.  
 - A NON LEAKING S.U carburetor. Preferably 46mm round top. 36mm flat can work to a certain extent. 
 - NON LEAKING 240z/260z Intake manifold. 
 - 240z heatshield and its components recomended.
 - New Intake/exhaust gasket HIGHLY recomended. 
 - Fuel pressure regulator OR 3 psi Fuel pump. or, both. 
 - 240z/260z Fuel line OR Rubber fuel hose and Brass tees, hose clamps. 
 - .100 nozzle (if it doesn't have it) and a SM Needle (available at Ztherapy) 
 - Long wire and a switch for 82~83
 - JB weld and Metric bolts can come in handy. 
 - Bunch of vacuum caps. 
 - Bolts/Studs for the Intake 
 - Extra linkages for 46mm. for 36mm you will need to custom fab a cable set up.
 - Fuel filter 
 - Dual choke cable and lever of your choice.
 
-The tools 
 - Metric ratchet/Torque wrench set. 
 - Unisyn 
 - Screw driver set 
 - Might need a reuter with cutting capability. 
 - Mirror and a flashlight 
 - LOT of rags. I mean ALOT. 
 - Pan, bottle, funnel , catch etc could come in handy.
 - Penetration oil of your choice. 


Step 1: REMOVING THE EFI
 
1. Start off by relieving fuel pressure. You should be able to by disconnecting the fuel pump and let the car run till it dies. 
2. Disconnect battery. Start dissconnecting the EFI connectors one by one, lableing them as you go just in case. 
3. Get a bottle and funnel as well as rag ready and start disconnecting the hoses. This includes the coolant line going through the throttle body, Fuel lines etc. Vacuum lines (lable them), Crank case hose, valve breather etc. 
4. Take off the old EFI fuel components, EFI fuel filter, regulator, fuel line, injectors (injectors should be able to come off as one with the fuel line) 
Part of the fuel line is attached to the belt pully. 
5. Remove all the junk thats on the EFI if it gets in your way of unbolting the manifold. The Brake vac heat shield too for easier access during the conversion.
6. Get your Ratchet wrench, mirror and flashlight.  The top 4 bolts are easy. cheesy. But the lower 6 bolts / nuts that you have to loosen (don't have to pull out completely.)  As seen in the picture below, The 3 exhaust manifold bolts can remain on there if you're planning on reusing the intake/header gasket (NOT RECOMMENDED but if you're not guna replace it, atleast put some sealant on there) 



7.ATTEMPT bolting off the EGR tube located all the way at the end of the manifold towards the driver side at the bottom.  If that doesnt work, then maybefrom the bottom and on the exhaust manifold side.
- If that doesn't work, just cut it off as seen in picture above. It's made out of Adamantium so good luck.  I JB welded a Nut to mine. it works lol. 
 
8. Take off the exhaust manifold and replace the Gasket if you can.    
9. Slide off the EFI linkage piece on the firewall side.  

 
Step 2 : REPLACING FUEL PUMP (if you're doing regulator, skip this) 
 
The 280zx fuel pump can be located in the right rear passenger under side. Easier if you jack your car up.
 
1. Usually there won't be any fuel left, But wear a goggle and get a rag just in case.
2. Spray some penetration oil and remove the hose clamps, Disconnect the fuel pump and bolt the pump off. 
3. The 280zx pump has a unique shape. If your low psi fuel pump is threaded, get some brass fittings and teflon tape to get your pump to the shape you need.  Or you could get some rubber fuel lines and play around with it.
4. While your under the car, get a multimeter and see which side of the connector is positive and which is negative. Get a friend to turn your car to where fuel pump will usually run.  label the connectors, 
5. Connect the new fuel pump and clamp all hoses back togather. 
 
Step 3 : INSTALLING THE MANIFOLD / CARBS

Refer back to the picture at the top, you will need 8mm x 1.25 40~45mm ish.  get however many you need. 
 
1. Slide in the Carburetor linkage thing to the linkage near the Hood release. It should be shorter than the EFI one. (for 46mm) 
2. Slide the intake manifold without the carburetor, It will be less hassle to bolt on. 
3. Bolt down the intake manifold / exhaust bolts to Specified torque. 
4. Optional, but you can connect the coolant hose that used to go to the throttle body to the intake manifold if it has one. But this was used to warm up the manifold quickly and was not meant for cooling....   You can bypass this coolant line by either returning it to the sensor housing where it used to end up or deleting it all togather with bolts etc.
5. Slap the carburetor on, don't forget about the center throttle linkage piece, bolt it on. 
6. Check your Fuel bowl float setting before you connect the fuel lines. 
7. Install heat shield and its springs if you have one. If you don't, fabricate your own spring tensioner or a heatshield to attach the spring to. 
8. Connect all remaining lines.  Dist vacuum, Fuel lines, Crank case stuff. throttle linkages.  I recomend putting clear fuel filter for visual of how much fuel is in the system. 

Step 4 : INSTALLING DIST FAKE SIGNAL SWITCH (for cars with E12-92 dist unit, 82/83 only)

The 82/83 ZX came with a E12-92 distributer which had variable retard via coolant temp and throttle position. 
Because we deleted one of the two inputs or both, we need to send a fake signal after the engine warms up, 
 
1. there will be a 2 pin connector on the top of this box on the dist. either cut the connector from the EFI or get some new ones. Both pins are POSITIVE, pull 12 volts out of the interior and put a switch. connect it to EITHER ONE of the pin or BOTH to control the timing retard manually. 

This switch should be turned on after you release the choke. It does enough to the dist that it can change idle by few hundred rpm. 
 
Step 5 : FINISHING UP THE BITS

 
- install choke cable.  Get creative and find a hole in the fire wall and a place to put a choke lever. Currently, mine is hanging around next to my seat. 
 
- pressurize the fuel until the clear fuel filter is full or near full.  Inspect all fuel lines and connections visually and with your nose. as well as your hand. Gasoline will have a very cool feel when you touch it with bare hands. 


And thats it, there you have it a Carb'd 280zx for all the haters.  Go google or youtube how to tune a S.U carb or go buy a dvd from Ztherapy. Its simple enough. 
 

 
 
 Hope you guys enjoyed the Read :) Have fun with your S.U carbs. 
 
 

[john510]

Have you driven this yet ? im thinking your'e gonna be a little down on power with 38 su's on an L6.

[Ryoskatekov]

Have you driven this yet ? im thinking your'e gonna be a little down on power with 38 su's on an L6.

Already drove it. Kinda restricted over 5000 but who does that in a daily ZX anyways? Lower end is super happy. 

[Zmike]

What did you do with the ecu and related harness wires?