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Xs400j problems

Discussion in 'The Garage' started by Ryder Desmarais, Nov 20, 2019.

  1. Hey guys I have a 82 xs400j. I've had it for a a good few months in that time I have put on about 3000 kms and it's been a little rough.. I have replaced some superficial parts and seals. I was warming the bike up this morning and getting my gear on when I couldn't hear the bike so I went down to turn it over again (thought it idled down in the cold weather) but I couldn't get it to turn back on. Any ideas on why this could be happening, I have had problems with it stalling before.
  2. Read manual and go through the usual list, then post any actual diagnostics you've done if you want help.

    Carbs, valve clearance, timing, check plugs, battery voltage, etc. Sounds like some deferred maintenance is overdue
  3. Went through carbs like a month ago. New plugs, new gas cap gasket( old one was fucked) oil change and all that normal shit even went through the wiring harness... battery is strong at like 12.7 or 12.9 volts
  4. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    So the bike stalled when you let it warm up and it wouldnt start again? Did it crank over?

    If the battery reads 12.7v, its low. Leaving the bike idling will only drain this even lower and it wont be enough to keep the engine running. The bike wont charge at idle speeds. Electronic ignitions need good voltage from the battery and you must produce charge above idle. You should see 14v+ above idle.Cranking the bike with a low battery will pull power away from the ignition. Get a new battery.
  5. xschris

    xschris a lifestyle not a trend Top Contributor

    12.7-9 volts on the battery with the bike off is perfect. 14-14.5v is at 5K rpm's or so. Idle 1200 rpm's should be around 13 or so. With these dohc bikes being e-start only it's good to not let them idle a lot and drive them at highway speeds so the batteries can get a good charge. If the volts drop lower than with the bike off volts there is a charging issue.
    buztabuzt and Ryder Desmarais like this.
  6. yes it does crank over and i did buy a new battery and its reading about 14.7 to 14.9 my dad tells me it going up and down between those #s indicates that the alternator still works
  7. Addison

    Addison XS400 Enthusiast

    Does anyone have any thoughts on a DOHC being topped up periodically (say, driven daily and then tossed on a NOCO trickle charger overnight once every two weeks) if only using it for short commutes?

    I think it would be a good idea and easy enough to do if you aren't really ripping the bike around too much.
    I will be using my 83 DOHC as a daily driver, but only for a ten minute commute at 50km/hr (haha..) so I'm wondering if I should be periodically topping that battery off (newer battery) on the charger.

    Easy enough to do, but I'm new to the bike world and curious if charging the battery while it's on the bike can cause any issues at all.. I don't see why it would, but I may be missing something obvious.

    Sorry to hijack the thread, just curious.

    @Ryder Desmarais as for the stalling issue I think the above posts pretty much covered it, with the battery. Same thing happened to me when I first got the bike a few months ago, cold weather starts ran fine but then stalled and wouldn't fire up as the battery voltage had dropped too low.

    Good luck.

    PS- Post a few pics when you get a chance! Is the XS400J the Seca? Anyone know the Maxim number (is it the K?)?
  8. Did some tinkering and its running but only with the gas on prime..

    Attached Files:

    buztabuzt likes this.
  9. Addison

    Addison XS400 Enthusiast

    cool looking bike, unique front load saddle bag there too.
    Wondering if perhaps there is a fuel supply issue from the petcock if fuel can only flow from prime position.

    I would first replace the gas lines, install an inline fuel filter, remove the petcock assembly and inspect those elements, disassemble and reassemble the petcock to become familiar with how it functions, and also inspect the tank.

    Could be many potential issues stemming from this process: debris inside the tank, poor fuel lines, then of course that leads to dirty carbs etc. Best of luck looking through those items, let me know how it goes.
  11. so i have gone through the petcock and put fresh gas in the tank i didnt seen anything wrong with the fuel system... replaced the fuel lines.. and im still stalling
    it uasally stalls when i come to a stop but sometimes wile im moving at 50, 60 kmh
  12. Addison

    Addison XS400 Enthusiast

    I'm wondering if the stalling while driving issue is more of an electrical issue.
    I'm stumped as well, I have no idea as I'm very new to this but it sounds like you've eliminated the possibility of it being a fuel supply issue. I honestly do not know where to go from there, I would try checking wires to see what happens. Is there anything that is consistent when it stalls at a high speed? For example are you hammering the throttle? Is it while decelerating? Cold weather? After engine is up to running temp?
  13. pcream

    pcream XS400 Enthusiast

    You had said earlier that it will only run with the petcock on prime. Is that still true now that you have taken it apart and presumably cleaned it? Is the vacuum tube connected to the intake? Does the petcock function correctly:

    1: When it is on run/reserve, does no gas flow while the engine is off?
    2. When it is on run/reserve, does gas flow while the engine is running/cranking over?
    3. When it is on prime, does gas flow freely all the time?

    The answer should be yes to all of the above, if not then the petcock is not functioning correctly and might be leading to you running out of gas in your carb a minute or two while riding. If the petcock is all functioning correctly, I would move onto to checking the carbs again, sometimes it takes two (or three!) teardowns to clean out all of the gunk and/or find components that no longer work, especially if you don't have an ultrasonic cleaner.
  14. The petcock on this bike has "ON" "RES" and "PRI" it flows freely on prime and reserve but does not flow freely on 'on'... I think it maybe be float height and if its not that maybe rusty tank or bad back pressure on the exhaust .
  15. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    The petcock has nothing to do with float levels or rusty tanks or back pressure.

    If the petcock doesnt function 100% on all positions, it needs to be replaced or rebuilt.

    if it stalls when you are riding and it will start back up a moment later, you most likely have a fuel starvation issue. Its recommended that you use a clear inline filter as well as the built in filter in the petcock.

    You said you rebuilt the petcock? Did you test it? Did you put a vacuum line on it and see if it works properly? Did you check the flow rate?

    The next step after that would be to check the carbs for sticking floats, they usually stick open though and you end up getting fuel dumping into the filters. I havent heard of floats sticking closed...?

    are the carbs synced? That will make the bike stall and idle poorly and cause stalling.

    Ive had stalling issues that turned out to be bad grounds and battery connections.
  16. So my dad and I (he's a harley Davidson mechanic) went through the bike again and we realized that it was getting almost no spark at all, we pulld the ignition coils out and tested them, they were ok. (Brand bew battery and spark plugs) so we figured after looking at the wiring diagram it had to be either the pickup coils or the tci unit . We manage to get a tci unit at a local motorcycle salvage... and it worked!!! 2 days later after install tho
    buztabuzt likes this.

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