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No power......couldn't pull skin off rice pudding

Discussion in 'The Garage' started by Ivant1066, Aug 1, 2022.

  1. Ivant1066

    Ivant1066 XS400 Member

    Hi all,

    Need help, my 1982 xs400 has very little power, I think a 50cc would beat me off the line & it is just gutless, it starts fine & ticks over no problem, had the carbs cleaned, new plugs, new leads, new rec/reg, it's with my local bike mechanic but I think he needs ideas......any thoughts appreciated
     
  2. CaptChrome

    CaptChrome XS400 Addict

    Welcome to the forum!

    I guess I would start with the very basics. What sort of compression do you have in the cylinders? Does it smoke under acceleration? How does it rev in neutral? What does the bike sound like under load? Is the bike stock, or have there been changes to the air intake and header/muffler? Does the fuel tap flow a lot of fuel or just dribble?
     
  3. Ivant1066

    Ivant1066 XS400 Member

    Thankyou for the welcome.

    Thanks for all the suggestions, it doesn't smoke but that's the only thing in the list that's definite. It isn't stock.....it has cone air filters & the header & silencers have been changed. Compression is a definite to check, when revved in neutral the pick up to me doesn't feel responsive.
     

    Attached Files:

  4. CaptChrome

    CaptChrome XS400 Addict

    After seeing your picture (nice looking bike BTW!), I am thinking you probably have an issue with the carb tuning given the pod filters and the shorty exhaust. The CV carbs used on these bikes have a reputation of being hard to get tuned properly with pod intake filters. Some builders claim that they can get them to work, but I have never seen a good "recipe" for jetting and tuning. Longer intake stacks seem to be one solution that might be promising. You might search the forum here for jetting/tuning tips for pod filters. The engine will probably do better with slide valve carbs, but that is a pretty big expense.

    However, do the easy to check stuff anyway. Then worry about the carbs.
     
  5. Ivant1066

    Ivant1066 XS400 Member

    Thanks again CaptChrome for the feedback. I had heard before about pod filters being a pain & not being easy to jet/tune easily, the shorty pipes as you said won't help either. As you say I will get the easy stuff checked first, but I have a feeling your hunch about the carbs will be right.
     
  6. Kitchi

    Kitchi XS400 Member

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    I would start to see if it it running on both cylinders. Are both exhaust pipes heating up? (near each cylinder) If they are not I would start investigating why the cylinder isn't firing.
    check compression
    check to see if you have Good spark.
    look at the spark plug. Is it wet? I yes it might be over fueling causing a spark plug fouled.
    If it is only running on 1 cylinder you may have to check the resistance on the pickup coils along with primary and secondary of the ignition coils.

    These bikes are pretty simple it dose not take much for them to run.


    I just went though this on my on my 81 xs400. I found 2 issues
    1. my tci box was defective (I was able to fix it)
    2 that same cylinder the carb needle seal was bypassing.So I rebuilt both carbs.
     
  7. CaptChrome

    CaptChrome XS400 Addict

    @Kitchi - Do you mind posting what you found in your TCI and how you fixed it in another thread? Might be helpful.
     
  8. spectra

    spectra XS400 Junkie Top Contributor

    Had an 80 and well ended up running the H pipe with unis........... worked out great......... both SOHC builds I did I used the H pipe and unis........ even my latest uses the unis...... not sure what it is but the regular pod filters you see I think are junk......
     
    CaptChrome likes this.
  9. Ivant1066

    Ivant1066 XS400 Member

    Thanks for the info guys........sorry please forgive my ignorance, but can you explain "the H pipes" & "unis" in lamens terms please. Thanks.
     
  10. Kitchi

    Kitchi XS400 Member

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    on the stock exhaust if you look under the motor there will be a pipe connecting both exhaust pipes together. that is what is called a "h pipe". If you look at it it is in the shape of an H.

    I not sure what Spectra means by unis
     
  11. Ivant1066

    Ivant1066 XS400 Member

    Thanks Kitchi......I did think that's what it might be, but thanks for clarifying.
     
  12. CaptChrome

    CaptChrome XS400 Addict

    I think Spectra is referring to the intake manifold here. Here is a pic of what that looks like and why it gets called an H-pipe...
    Carb Intake boots2.JPG

    The unis are pod filters make by Uni Filter. Search for "uni pod filter" and you will find out what they are. However, I will let Spectra correct me if I misspeak (which I seem to do a lot, just ask my wife.)
     
  13. Kitchi

    Kitchi XS400 Member

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  14. Ivant1066

    Ivant1066 XS400 Member

    Hi Spectra,

    Could you tell me the code of the "uni's" you use please. Thanks.
     

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