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Engine randomly dying

Discussion in 'The Garage' started by jonjkim12, Aug 21, 2014.

  1. jonjkim12

    jonjkim12 '77 XS360 Owner

    1977 XS360 - Stock Engine, well-maintained

    Hi all,

    Since I've gotten this bike, if i don't change gear closer to 6k (no lower) it seems like the engine begins to run rich. I can smell gas from the exhaust and there's been afterfire once in a while. Most of time, once she begins running rich, within a few minutes, i'll lose all power and I end up having to pulling over. She'll start right back up (1st kick), but will run rich, and typically lose power again if i don't let her sit for a while.

    Everytime I'm on the bike, after riding north of 45mph, I notice that she'll idle around 2-2.5k (at start up and before entering a longer straight away she idles around 1.2-1.5k)

    I was told not to shift too low (3k - 4k) and start shifting it higher. My mechanic that told me that also did a full cleaning of the carbs, and full check up (plugs and all). The problem got better, but still persisted (especially on hills where I had to keep her higher than 6.5k)

    Recently the problem got really bad, within a 20min ride, the engine just quit (going around 45mph) all of a sudden. I haven't noticed any patterns. It also shuts off when I downshift to a redlight and pull in the clutch. The moment the clutch is pulled in, it completely dies. But it'll start right back up no problem (only kick, no electric start).

    Anyone have any idea what's going on here? Not sure if the initial problem is the same problem as what's been happening recently, since it never died when i pulled the clutch in at a stop before.

    Clutch? Battery? Plugs? Timing?
  2. xschris

    xschris XS400 Guru Top Contributor

    When was the last time you set the points/ valves and synced the carbs with a manometer? When you cleaned the carbs did you fully take them apart to clean them and replace all the seals and o-rings. The xs360 carbs have choke gaskets and needle jet o-rings that go bad and should be replace from time to time. I would also do a compression test on the motor. Post a few pics of the bike so we can see what you have.
  3. jonjkim12

    jonjkim12 '77 XS360 Owner

    Hey xschris,

    I'll definitely post some pics shortly. I know the carbs were cleaned and synced a few weeks ago when the problems really became apparent (before the dying when the clutch is pulled in).

    I checked the spark plugs last night, and after putting them back in, now she doesn't idle. If i let off the throttle it just kills in the engine, not sure if this is a spark plug gap issue (i literally just pulled it out then put it back in after checking it).

    I'm going to play with the idle screw later see if that'll fix it. As for the clutch killing the engine, i checked the free play on the clutch and it was set exactly to what the manual says it should be set to.

    im stumped.
  4. xschris

    xschris XS400 Guru Top Contributor

    Have you turn the idle screw up? That may be all you need. How did the plugs look?
  5. jonjkim12

    jonjkim12 '77 XS360 Owner

    I haven't, it was getting late last night. It's weird because the mechanic set the idle screw to where he said it was "perfect" and it seemed to be, but since i checked the spark plugs, it idles as if i turned the idle screw all the way counterclock wise and keeps dying if i don't keep on the throttle

    plugs looked okay (though, from the charts i've seen that seems very subjective) they were white (not powdery, just white colored) with a little tiny bit of black almost like i took a light to it and just charred a little part of it, with the metal threaded part at the tip black.

    could this be a throttle issue? i'm not super mechanical, but isn't there a adjustment where i can set the throttle to open a little?

    i've also wanted to check to see if the gas cap is venting, but not sure how to check that either. i read there there should be a tube that vents it? but also a tiny hole on the gas cap.
  6. Lou Ranger

    Lou Ranger Former xs400 Luddite Top Contributor

    Chris will know what's best to do with your carbs.
    As to the engine cutting when you disengage the clutch, taking all the load off the engine shouldn't cause it to die - just maybe rev a touch higher.

    Unless, there is wiring involved - and I think there is.
    If your bike has a safety switch which allows the bike to be started in gear but only if you pull the clutch in, couldn't that switch be faulty or shorting out? My Maxim was wired that way - though I was lucky and didn't ever have a failure myself.
    Might be worth checking it for insulation, grounding, connectivity, tightness etc.
  7. xschris

    xschris XS400 Guru Top Contributor

    This plug came out of my 79 with 33k miles on it and 4k on the plug. They should look about like this. When you are talking about the idle screw do you mean the one in the middle with large plastic cap on it? That one turned in will open the butterfly valves in the carbs raising the idle. The two smaller ones on the sides of the carbs are your idle mix screws and adjust the fuel/air mix from idle to 1/4 throttle. They should be set 1-1.5 turns out from lightly seated. Even with pods and a free flow exhaust. The xs360 carbs run a lot richer than the xs400 ones do.

    Attached Files:

  8. jonjkim12

    jonjkim12 '77 XS360 Owner

    So i was playing around with it last night.

    My plug looks very similar to yours, maybe a little bit cleaner (think it was replaced before i bought it) and yes i the plastic cap is what i meant. i didn't know there were more screws (learning a lot here).

    So i ended up playing with the plastic cap and turned it clockwise until it idled closer to where it used to be 1.2-1.5.

    I see! well, i'll have to try that today. so basically turn it in until it resists, then turn out 1-1.5 turns?

    is it possible that the idle screws or the plastic cap turned out or in at some point without me doing it myself? that's odd.

    when i adjusted just the plastic screw last night, got her to idle, it did smell a little rich (gas smell). typically should i adjust the idle screws before adjusting the plastic screw?
  9. xschris

    xschris XS400 Guru Top Contributor

    Set the small screws on the side to 1-1.5 turn out from lightly seated. With the bike warm set the large middle one to 1200 rpm's. You should re-sync the carbs with a manometer just to make sure the carbs are balanced after.
  10. jonjkim12

    jonjkim12 '77 XS360 Owner


    So i re set the Mixture Screw and Throttle (Plastic) screw, Everything seems to be good for now. I have to take it out on a long ride to see if the main issue still persists. She actually died twice when i tested her with the new set, but i think i may have just set the Throttle Screw a little too low. New spark plugs on the way.


  11. jonjkim12

    jonjkim12 '77 XS360 Owner

    I guess that way i uploaded those pictures didn't work. I'll try to figure it out.

    As for the bike, i got it into work fine today no issues. But while i was adjusting the mixture screws (after watching a youtube video on it). I noticed the guy on youtube mentioned an air screw. is this a different screw, he said it would be closer to the air box or in my case the pods. couldn't find it though.
  12. xschris

    xschris XS400 Guru Top Contributor

    He must have been working on a vm style carb. Our bikes use a cv type carb. The only screw for fuel/air adjustment is for the idle circuit. And that was the one I showed you in the pic.
  13. jonjkim12

    jonjkim12 '77 XS360 Owner

    got it! Thanks Chris.

    So i've noticed that when i get the bike running at idle, if i turn on the headlight, it kills the engine. From what i've read some ppl have fixed it by replacing the stator. I believe the bikes PO replaced the stock battery with a smaller one for looks. But i'd like to be able to ride when it's darker outside.

    Is this the general consensus on this issue, a stator issue?
  14. xschris

    xschris XS400 Guru Top Contributor

    If it runs fine with the light off and the bike is charging at the battery ( 14.5 volts at 5k rpm's) the stator is fine. I would say your head light switch has a short in it or something is wired wrong.
  15. jonjkim12

    jonjkim12 '77 XS360 Owner

    I haven't check the charge yet. I still need to buy the right tools for that. But that's good to know, i wasn't aware that wiring issues could cause the engine to die like that. But i'll start researching that. I should probably mention the neutral light doesn't work either, and the gauges tend to wobble a bit, not very steady.

    this should be interesting, time to open up that wiring map, might as well just be scribbles.
  16. jonjkim12

    jonjkim12 '77 XS360 Owner

    One more question:

    where are two mixture screws for our bikes, correct? one on each carb? all these youtube videos only show them adjusting one.
  17. xschris

    xschris XS400 Guru Top Contributor

    On the xs360 you have one per carb. This adjusts the fuel/air mix from idle to 1/4 throttle. For 1/4 to 3/4 throttle it's your needle and needle jet and 3/4 to full throttle is your main jet. If your bike pulls good up to the red line your jetting is good.

    Attached Files:

  18. xschris

    xschris XS400 Guru Top Contributor

    Sounds like a grounding issue. The cables for the speedo and tach most likely need to be cleaned and lubed.
  19. jonjkim12

    jonjkim12 '77 XS360 Owner


    thanks for all your help btw. This bike is still giving me headaches though. Its back to the original problem i had with her. When riding north of 45mph with the rpms around 7k, it'll just give out and i have to pull over, but she'll start up right away after that, but almost always with another hiccup within the next few minutes.

    the rich/lean symptoms always confuse me. but could this be the bike running either rich/lean, then causing the later hiccups? normally once it happens the first time, its guaranteed to happen again during that ride. i believe the mixture screws are 2 1/2 spins out.

    any ideas? this problem has been happening for a while, and every time i bring it to a mechanic they can never recreate it. could be me...
  20. jonjkim12

    jonjkim12 '77 XS360 Owner

    just read through the xs650 forum, one thing i found was that people who experience kick-back from their kick start were suggested as having ignition timing issues.

    i've noticed that for the past few weeks, when i kick my bike, it'll kick back at me almost like it was in first gear and i forgot to put it in neutral, except i didn't.

    could the timing be causing all these issues? was causing the timing to become unadjusted?

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