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XS400 top speed??

Discussion in 'The Garage' started by Vloukole, Nov 4, 2013.

  1. xschris

    xschris a lifestyle not a trend Top Contributor

    These speedo's with stock tires can be off by 15-20mph :wink2:
     
  2. FarmBoy72

    FarmBoy72 XS400 Enthusiast

    I'll just have to wip out the radar then :bike:
     
  3. Lou Ranger

    Lou Ranger Former xs400 Luddite Top Contributor

    Very inaccurate guages, tires with different rolling circumferences, different sprocket ratio combinations or a combination of all 3 would do the trick.

    If my tach was accurate, I would not want to take my engine for a long, slow climb up to 11,800 rpm though . . . :yikes:
    Radar or GPS would seem to be a good idea!
     
  4. Vloukole

    Vloukole XS400 Enthusiast

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    My bike wont reach 11800rpm. It bogs down after 8500rpm. Still trying to figure it out. Any ideas?
     
  5. willem

    willem XS400 Guru

    :laugh:

    how about tuning and syncing up the carbs, setting the valve clearance, lubing all moving parts, checking the brakes for dragging? Fresh oil, greased chain, set timing if you have points? Inflate tires too.. If it then doesn't rev past 8500 I don't know anymore :shrug:
     
  6. Lou Ranger

    Lou Ranger Former xs400 Luddite Top Contributor

    I don't think any of our bikes will reach 11,800 rpm (missed-shifts excluded).

    When you say it bogs at 8,500, do you mean in top gear when trying to hit top speed, or, does it bog in all gears?

    If the former, it may just be that the engine can't push any harder against the wind at top speed.
    If it can't get to its red-line in any lower gears then it needs work - likely tuning (unless it's due to reduced compression).
     
  7. Vloukole

    Vloukole XS400 Enthusiast

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    I will check the compression. The carbs aint perfect. What is the fix for low compression?
     
  8. Lou Ranger

    Lou Ranger Former xs400 Luddite Top Contributor

    I believe low compression can occur if piston rings are worn, cylinder walls are scored or valves are worn or not seating properly.

    But I only know the things I have read over the years - no first hand experience whatsoever. I wouldn't want to advise on what to do should you get low readings because some things are cheap and some are not and it's important to diagnose properly so you don't waste money on unnecessary parts or hours of labour.

    Apparently, if you get a low compression reading then you should take a second one after introducing some oil into the cylinders. If there is a difference between the dry reading and the wet readings, then this is a clue as to where the problem is.
    Inspection of and adjustments to valves are also good ideas.
    I believe all these are relatively easy and cheap to do.
     
  9. Vloukole

    Vloukole XS400 Enthusiast

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    Hopefully its the cheap fix. Ill need to buy a compression gauge.
     
  10. Scorpio1963

    Scorpio1963 XS400 Guru Top Contributor

    First of all do a wet compression test,if you don't own tester go through the loan a tool program from stores like autozone,Advance auto or Oriely`s.
    Next if you get low reading like Lou R said it could be worn rings and cylinder walls.Valves not seating all the way cause of carbon build up.None of these are easy fixes they require a partial tear down at least.You want numbers in 140-150 range on your compression readings.
     
  11. Lou Ranger

    Lou Ranger Former xs400 Luddite Top Contributor

    With luck, everything will check out fine and you will be reduced to becoming a carb cleaning expert like most of the members on the Forum. . :banghead:

    Unless you break some fragile little part in the process it will cost you nothing except time, frustration and likely a bit of your sanity. Good luck.
     
  12. Scorpio1963

    Scorpio1963 XS400 Guru Top Contributor

    Loss of sanity priceless:laugh:
     
  13. xschris

    xschris a lifestyle not a trend Top Contributor

    Unless it can't be fixed:doh: We have seen a lot of that too.:wink2:
     
  14. Vloukole

    Vloukole XS400 Enthusiast

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    Update on the limited revs(8500rpm): The fix was changing the needle clip position 1 down from the center(4th notch now from top). Was able to take it to 9000 easily and felt like there was more left.

    Another problem is that when I take it for a cruise around town it suddenly start to run one cylinder and then dies and wont start. Ill let it sit for 2 minutes and it goes again but repeats the problem after 3km. One spark plug has an adaptor and a nice tan colour but the second spark plug is to rich(sooty).
    The plug with the adaptor missfires a little bit. Any ideas?
     
  15. 16VGTIDave

    16VGTIDave XS400 Guru Top Contributor

    At full throttle, above ~7000 RPM, your bike is getting most of the fuel from the main jet. The needle is fully extended before 8000 RPM. You will probably find that your bike is running rich at 1/2 throttle now. This may be the cause of your stalling.

    I'd suggest returning the needle clips to the previous position and following the testing and tuning procedure described here.
     
  16. Vloukole

    Vloukole XS400 Enthusiast

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    Great read thanx. I think alot has to do with my float height. Is it safe to adjust one of the mixture screw 3 turns out and the other only 2 turns out? Any chance of damage anywhere?
     
  17. 16VGTIDave

    16VGTIDave XS400 Guru Top Contributor

    Adjust the Pilot screws as required to maintain a good idle. The suggestions to start with a certain number of turns out is just a starting point to get the bike running. Many people adjust the Pilot screws out further than they should to try to compensate for a Pilot jet that is too small.

    Follow the guide and you will have a well adjusted and happy bike. And that will make you happy as well! ;)
     
  18. Vloukole

    Vloukole XS400 Enthusiast

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    Okay but do you think that the spark plug adaptor is the cause of that plug to run leaner than the "normal" plug? The adaptor reduces the depth of the plug.
     
  19. arfstrom

    arfstrom XS400 Guru Top Contributor

    http://www.motorcyclespecs.co.za/model/yamaha/yamaha_xs400 77.htm

    from previous marked website. Personnelly, I couldnt get mine over 85 mph.
     

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