Hitachi to HS6 carb conversion & rebuild | The Z Club of Great Britain
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Hitachi to HS6 carb conversion & rebuild

Discussion in 'S30 (240Z,260Z,280Z) Engine' started by Farmer42, Apr 24, 2018.

  1. Farmer42

    Z Club Member


    I have recently swapped my Datsun Hitachi carbs to British HS6 SU carbs and I thought it may be worthwhile posting up some tips and pics when refurbishing them to the correct Datsun spec.

    I have attached a Word document to talk it through. I am happy to try to answer any questions although I am no technical expert and relied very heavily on a very helpful guy at Burlen Fuel Systems.

    Happy ReadingEXTRA:)


    Attached Files:

    franky, toopy, Huw and 1 other person like this.
  2. Huw

    Z Club Member
    Staff Member

    Good write up Paul. :thumbs::thumbs:
  3. AliK

    Z Club Committee
    Committee Member

    Really great write up - we should make this a Sticky as I'm sure it will be asked / searched for in the future.

    Nice Job Paul!

    Ps. You paid a heck of a lot less than my ZT carbs, in fact less than half and being bigger, yours probably breath more easily / better too!
  4. Farmer42

    Z Club Member

    Thanks guys.

    Forgot to mention a couple of things.

    Firstly, HS6 carbs have a pipe that the crankcase breather hose on British cars attaches to (one on each carb). It is not needed on a Zed as the breather pipe attaches straight to the inlet manifold. You therefore need to blank them off otherwise it will suck air in and the car will run erratically. You can buy pipe caps (car builder solutions) or you can use a piece of fuel hose and clamp a bolt in the end (bodge!!:EXTRAp).

    Secondly, British SU carbs run on a fuel pressure of about 2.5 - 3 PSI which I believe is lower than Datsun Hitachis. If the float chamber floods, you will get fuel squirting out of a breather hole under the fuel inlet pipe on the float lid. If this happens, the pressure is too high and is overwhelming the float valve (they are delicate little things and don't like to feel pressured!!EXTRA:D). It will probably happen if you are running an electric fuel pump especially a Facet red Top. I had this and got over it by putting a fuel regulator in the delivery line.

    Thirdly, If you do buy new float lids or have stay-up floats, you will need to set the float level. You do this by turning the float lid upside down and simply bending the metal tang as near to the float as possible. The gap between top surface of the float and the float lid is 1/8 inch or 3.2mm. Easiest way is to use a drill bit and lie it across the lid and adjust the float until it touches the drill.

    Finally, if you do need the conversion collar to convert the needle from variable or biased needle to the fixed jet needle, the part number is ABF193.
  5. dav118118

    Z Club Member

    I would think 2.5 psi is ideal for early dome top hitachis? I have a pressure regulator and have it set at 2 psi and seems fine. Does anyone know the correct pressure? Admittedly I haven’t been redlining the car so can’t comment on lack of fuel at the top end
  6. jonbills

    ZClub Administrator
    Staff Member Committee Member

    Yes it’s 1.5 to about 3.5 for SU and Hitachi (and Weber and Dellorto and...) the picture is confused by US forums’ assertions that carbs run 5 psi. That’s Holley’s spec, and normally SU/Hitachi/Weber/Dellorto tolerate it so it goes unchallenged.
  7. Farmer42

    Z Club Member

    Hi all.

    My attention has been drawn to a typo in my write up. The part number for the piston spring is AUC1170 not AUD.


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