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4G5 carb jets, pilot plugs, power and general

Discussion in 'The Garage' started by Gra900, Feb 3, 2020.

  1. Gra900

    Gra900 XS400 Addict

    Rebuilt most of the 400SE but found it had two carb related symptoms. First it’s tickover would slowly rise as it warmed up, so would only then tickover ok with the choke out.
    Second it would go above about 40mph.
    The PO had had the carbs rebuilt so I had assumed they would be Ok, but on strip down I’ve found there’s no plugs on the pilot jets and the needle jets have white deposits inside.
    I also have the tapping points on the inlet boots joined by a bit of fuel hose. Running standard filters and a 2 into 1 going into a single silencer from a triumph 865 cc.
    Jets as fitted are
    Main jet 125 - now this is different to all other Xs which is normally 135. Is that why some people say these engines are 27bhp rather than 34bhp?
    Pilot - 42.5
    Needle 5HZ17
    Needle jet looks like 271 but hard to read
    Pilot air jet 150?
    No oring or washer on air screws, had been set to 1.5 turns, Haynes reckons 3.5
    Main question, how important are the pilot jet plugs

    ED9A2EEC-CB5D-482C-9539-150C69FC32B6.jpeg ED9A2EEC-CB5D-482C-9539-150C69FC32B6.jpeg
     

    Attached Files:

  2. Gra900

    Gra900 XS400 Addict

    Correction ——. It would not go above about 40 mph
     
  3. xschris

    xschris a lifestyle not a trend Top Contributor

    135 mains is a good start. Yes you need those plugs. Make sure your floats are set to 22mm. Your float valves look like the wrong ones. They should have rubber tips and a hoop on the end that holds the float. Your mix screws should have a o-ring, washer and spring on them. 3 turns out from a light seat is a good starting point. Not sure about your jet needle as the 80-82 sohc xs400 uses a different one.
    DSC03784.JPG
     
    Last edited: Feb 4, 2020
    Gra900 likes this.
  4. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    Theres differences in the camshaft that reduced HP figures for European models
     
  5. Gra900

    Gra900 XS400 Addict

    Hi .mike, so do you reckon bigger mains would improve top end?
     
  6. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    You will have to do plug chops to get some idea of whats happening. I think its also necessary to verify the ignition timing if you havent done that yet. Its easy to mistake a fueling issue with bad timing and it helps to eliminate that possibility. Youre better off being slightly rich in the end. Leave the needle and mix screws at factory settings and dial the main jet first. You should end up with 2 main jets that perform well enough. Then you tweak the mix screws and finally the needle height. That should get you close enough.
     
  7. xschris

    xschris a lifestyle not a trend Top Contributor

    Looks like at some point the carbs where re-built with a 82-84 dohc kit as the gaskets are wrong also for a sohc bike. Get the plugs and fix the other issues with them and go from there.
     
    Gra900 likes this.
  8. Gra900

    Gra900 XS400 Addict

    Found the right gaskets and float valves with hoops FCC1CCA9-A228-4C1F-9AE8-CC980B89DC49.jpeg
     

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