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Should I "un-de-tune" my Hitachi HSC32's?

Discussion in 'XJ Technical Chat' started by StahlMaster, Dec 25, 2018.

  1. StahlMaster

    StahlMaster Active Member

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    Per this website... "That being said, all of these bikes were jetted a bit lean from the factory, in order to satisfy EPA emissions requirements of that era. So even a stock engine can benefit from slightly larger fuel jets...

    I have my carbs apart for major rebuild and I'm wondering what exactly I would need to replace to "un-de-tune" my Hitachi HSC32 from my 1982 XJ650J Maxim here in Michigan, USA.

    I've read to go from #110 to #112 on the main fuel jet and from #40 to #41 on the air jet. Is that all? Just the jets?

    D



    This is just a photo of Carb #1
    Carb 1 Done Side.JPG
     
  2. XJ550H

    XJ550H Well-Known Member Premium Member

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    just the pilot jets. the pilot jet is what was being tested through the ports in the exhaust by the gas sniffer
     
    k-moe likes this.
  3. XJ550H

    XJ550H Well-Known Member Premium Member

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    check this site you could go with the Canadian specs
    http://xjbikes.wikidot.com/carb-specs
    Years & Models: 1982-3 XJ650 Maxim USA models
    Carb Manufacturer: Hitachi
    Carb Series: HSC32
    Carb Model ID: 5N800
    Main FUEL Jet Size: #110
    Pilot FUEL Jet Size: #40
    Main AIR Jet Size: #50
    Pilot AIR Jet Size: #205
    AIR COMPENSATOR Jet Size: #36
    Starter FUEL Jet Size: #40 (non-replaceable, in float bowl)
    Main jet NEEDLE ID: #Y-10
    Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
    Fuel Level in float bowls: 3mm +/- 1mm (.118" +/- .039")
    Idle RPM's: 1,050 rpms

    Years & Models: 1982-4 XJ650 Maxim Canadian models
    Carb Manufacturer: Hitachi
    Carb Series: HSC32
    Carb Model ID: 5N900 or 5U900
    Main FUEL Jet Size: #112
    Pilot FUEL Jet Size: #43
    Main AIR Jet Size: #50
    Pilot AIR Jet Size: #205
    AIR COMPENSATOR Jet Size: #36
    Starter FUEL Jet Size: #40 (non-replaceable, in float bowl)
    Main jet NEEDLE ID: #Y-10
    Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
    Fuel Level in float bowls: 3mm +/- 1mm (.118" +/- .039")
    Idle RPM's: 1,050 rpms
     
  4. StahlMaster

    StahlMaster Active Member

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    So I could go with:
    Main FUEL Jet Size: #112 (to replace stock #110)
    Pilot FUEL Jet Size: #43 (to replace stock #40)

    Thanks
     
    Last edited: Dec 25, 2018
  5. Jetfixer

    Jetfixer Well-Known Member

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    I upped jets in my 750 Seca ...main I put in a 124 ended up putting 120 back in , ran so much better and my fuel mileage was better .
     
  6. StahlMaster

    StahlMaster Active Member

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    Perhaps going from #120 to #124 was too much of a jump.
     
  7. Jetfixer

    Jetfixer Well-Known Member

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    The only other was 122 , honestly did not notice ANY. Difference in flat out speed .
     
  8. StahlMaster

    StahlMaster Active Member

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    I'm going to leave it stock. I really like to get the most MPG from these tiny tanks.
     

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