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Stalling @ lights

Discussion in 'Technical and Troubleshooting Torque' started by peon_feo, Aug 28, 2006.

  1. Hello everyone,

    So I've purchased myself a 1988 Honda NT400... now I have to figure out all the little niggles ;) First on the list is its nasty habit of stalling at the lights when I have the headlights on (I have a switch which lets me turn them off and on!) and am indicating. The idle speed seems to slowly drop.. and drop.. and drop.. until it simply cuts out. When cold idle seems to sit around 1k, when warm it sits up around 1.2k.

    I guess this is probably tied into its sometime-reluctance to start ;) When I go to start it, often it will sit there churning the starter-motor until the battery dies. In fact, whenever I start it I actually have to let _go_ of the start button to do it -- that is, the engine only catches when I'm not pressing the button. Finally, it generally won't start at all if the headlight is on. Turn it off, and it's more likely to start.

    Final possibly-related info: won't start at _all_ with the choke on, will stall if I start the engine and then put the choke on (without revving the engine high first). If I ride around with the clutch on a bit (up to around 2k rpm) I can have all my lights on/etc without a problem. Similarly, if I'm sitting at the lights and keep a little bit of gas on, she doesn't stall.

    These are work-arounds, though -- I'd like to FIX this issue. Thoughts? Suggestions? If possible, I'd like to do this work myself, but if that's not advisable, let me know (mechanical newb, but not an utter retard ;)

  2. Sounds like a lack of juice in the system, so probably alternator: there's just not enough there to run everything, so when it's running the starter motor there's not enough for spark and so on. I think I'd be taking it to an auto electrician that knows something about bikes...

    Edit: Or, for doing the work yourself, seeing if you can get hold of a replacement alternator and fit it. Trouble is I suspect new ones will be tough to get, and ones from a wrecker risk being just as bad or worse...
  3. Could it just be a weak battery?
  4. Yep, alternator or regulator.

    You can refer to the manual for testing.
  5. I suspect it's not just the battery, because the alternator should provide enough juice to keep it running when it's running... although I guess a flat battery acts as another major source of resistance in the system. I guess getting the bike running then disconnecting the battery and seeing if it still idles down/stalls when the headlights are on might help to eliminate the battery as the issue.
  6. Or it could actually be the wiring lume even. But unlikely.
  7. Check the battery has good tight un-corroded connections, especially the earth.
  8. Im new to bikes also, but what i'm about to tell you is a work around for when you actually do get the bike running (ie this will not help you with your cold starts).

    Does the bike die if you rev it a bit whilst your at the lights? If it doesnt die when you give it enough throttle to rev at about 2000 revs, maybe you can adjust your idle cable thing. That way, you'll have enough revs to sustain your alternator, which is charging up the battery - which is being used by the lights.
  9. Oh, she usually starts. Eventually ;) Although I did have to bump-start 'er this morning. (Grr). If I'm riding at night, I do have to keep the revs up around 1500-2000rpm or so -- then it doesn't cut out. But that's not really a _fix_ -- it's a work-around ;)
  10. chances are you have a really old battery that isn't holding charge. check the voltage of the battery with everything off. it should be more than 11V.

    when you bike is running properly (with all the lights on), check the voltage across the battery. it should still be around 14V. if it's less, try again with a good battery. if its 14V, then it's your battery. if it's still the same, your alternator is not putting out enough, or the regulator is keeping it too low. mostly like the regulator/rectifier.
  11. Try the battery first including the terminal connections and then the alternator or regulator. A multi metre might come handy for the job.
  12. It could be the battery, so the first thing to do is check the voltage supplied, not running, at idle and at revs, as described above.

    Also consider:

    What's your starting proceedure?

    Do you use any choke?

    I'm not sure what the standard idle is on this bike, but that sounds like a minium. Another 100 rpm may see the alternator charging better and the whole problem going away.
  13. Okay, so I broke out the old multimeter on Wednesday when I was home sick, and naturally the bike behaved perfectly! Started first prod, no sign of stalling with the lights on. Multimeter reckoned it had ~11-12V across the battery when off, 14V when idling, still 14ish with lights and indicators (although it was showing a bit of a tendancy to drop very very slowly).

    'Course, when I went to start her Thursday she wouldn't go at all. Plenty of starter-crank but no go -- had to roll-start 'er. And yet, this morning she started first prod! NB: I don't use choke to start, but once it's going I do crank the choke about 50% (~3,000RPM) to warm up whilst I gear-up.

    A mechanic I spoke to reckoned it was probably the battery, and that would explain why she'll start some mornings, but not start others (weather in QLD is never exactly cold enough to be an issue! ;) I'm planning on taking the bike to some friendly battery specialists tomorrow, who reckon they can tell me in seconds flat whether it's the batt or not -- if it's not, next culprit to test is the rectifier....

    Finally -- can anyone suggest what might be causing rattling noise to occur @ about 3-3,500RPM? A nasty little voice in the back of my head keeps muttering "tappet valves" but, given that I've never heard what they sound like, or indeed know when they'd start making noise.....
  14. Most modern bikes need choke to fire then not much after that. try that starting proceedure.
  15. Ahh -- what's a modern bike, though? ;) This is an '88, and not exactly a sophisticated machine (at least, that's what I gather...)
  16. Showing my age, but I would consider that a modern bike. Give it a go. whats to loose?
  17. Nothin' ;) And I will give it a go,

    Not sure that it will help the starting issue though -- the bike either starts perfectly first prod, or sits there chruning the starter. If it's churning the starter, it will only start when I release the START button.

    This leads me to thinking that it's not getting quite enough juice to run both the starter motor AND the sparkies at the same time. Given the variance in starting behaviour, I'm thinking the battery sometimes isn't holding sufficient charge...

    Or, perhaps I'm just smokin' de crack ;)
  18. It could be the starter is just cranking faster then the idle, without choke. so you only notice theturn over after you stop cranking.

    also check your battery terminal connections are good. If they are not then a limited current draw down may only be possible.

    I have had this before.

    Stick some aluminium foil between the terminal and leads, for a temporary solution.
  19. After a great deal of stuffing around, I took the bike back to the dealer last week and insisted they fix it -- the phrase "this is not roadworthy" worked wonders! They've swapped out the reg/rec and (after they flooded it trying to start it, backfired it, and replaced the spark plugs) she runs like a dream!

    Now I just need to get the bugger tuned! I suspect someone ramped up the idle/mix settles to compensate for the dodgy reg/rec, as when she gets up to a warm running temp the idle sits about 2k!

    Thanks for your help, everyone.
  20. If it's taking a long time to warm up, try backing out the idle mixture screw.

    this will give you a higher idle, when you first come off choke and will thus allow you to screw your idle speed down.