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CB250 Electical problem, wont start :(

Discussion in 'Technical and Troubleshooting Torque' started by Viator, Apr 18, 2009.

  1. Hi all. I'm trying to fix a cb250 for a friend because the bike has been left at my place. Problem is I don't know what the problem is.

    I can't get it to start. The symptoms are that when I try to start it it has no life like the battery is dead. I can't push start it. I've tried many times in different gears etc. I've even rolled all the way down a hill in 2nd and even with the engine and wheels turning still no life. I did catch a glimpse of the neutral light though so I got a split second of power from somewhere.

    It seems to have fuel and no spark (although I'm not sure). My friend thought it was a dead battery and so tried to charge the battery with a charger that was too powerful. I get the feeling that in doing this the regulator rectifier has broken? I'm only guessing this because I've read Hondas have problems with them. Also, I should mention I'm pretty sure the battery has charge.

    So if it is the regulator rectifier then how to do I confrim this? How do I even find it. I don't have the service manual.

    Any help at all would be greatly appreciated.

  2. before we get too carried away, remove the old battery.
    The electrics on the CB are very simplistic, I rebuilt one of these from the ground up for my wife, just a year and a bit ago (which I've since sold because she got knocked up and had an extra kid etc).

    Get your hands on a jump starter (very handy things to have) and hook it straight up to the leads that used to run to the battery.
    Try and start it.
    If this fails miserably, come back and we'll start other troubleshooting.

    My guess is that there is a completely dead cell in the battery, causing a massive voltage drop, which would make any current generated by the alternator/reg/rec be eaten up by the battery before it can have a chance to be spark.

    *you can also use jumper leads and any 12v battery (eg car), the jump starter is just so handy.
  3. Thanks Joel. I got a result but not the one I was after.

    After hooking the bike's battery up to a idling car, all the bike's lights came on (yay!) but couldn't get it to start. You could hear the starter motor going crazy on the bike but the engine wouldn't fire itself up.

    I'm not sure if I've got one problem or multpile and possibly unrelated problems. Either way Joel thanks, I'm one step closer now.

    Also, I just tried it with my bike's battery in it and same deal. Starter motor goes, lights are on, bike tries its hardest, but the engine wont fire up. Checked the spark plugs and they were a tad oily and a tad carbony but seemed to be fine.

    So tell me guys, why does it seem like I'm getting no spark??
  4. ok, so we have the first problem sorted. The battery was cactus.

    From the info provided, there is fuel (for sure? and the fuel c0ck is on? and no inline filters are clogged?), and we have a working starter motor.
    The next thing is spark.

    Hook the bike back up to the car (no need to leave it idling, we wont use much power).
    You need to pull out a spark plug and firstly, have a look at it.
    you'll know if the plug is stuffed, just by appearance. If you are unsure, take a picture and post it.
    With the plug out of the motor, but still connected to the plug lead, earth the sparkplug somewhere on the motor that is accessible. You can earth it by touching any part of the plug, from the thread down, against any bare metal object on the bike.
    Whilst the plug is earthed, give the starter button another go, and keep an eye on the gap at the dangerous end of the plug. There should be good strong spark.
    Repeat for the other cylinder/sparkplug, and come back with results.

    BTW, what year model are we talking here, I have a full workshop manual
    with greasy fingerprints and dog-earred corners.
    It wont matter too much about the year model though, the inline twin 250 honda motor has been unchanged (more or less) for 30 years!
  5. Okay, just gave it a crack with only one of the spark plugs. It's sparking, but I get the feeling it's not a strong spark? Instead of it jumping across the bit that's referred to as the 'gap' it jumps from (hmm how to explain) the small circle bit to the bigger circle surrounding it. When I say the bigger circle I'm referring to the bit that's the 'inside' of the thread.

    The spark is blue and fairly short, say the length of the 'gap' or slightly shorter.

    Hope you get my drift.

    Cheers, appreciating all the advice.
  6. Just went to grab dad to show him my progress so far (he's no mechanic) and he managed to help. Who'd have thought my old man would know something. I showed him the spark and so he smashed the spark plug in an ape like fashion against the ground. I think this was his way of 'gapping' the plug.

    Anyway, gave it a shot after that and it fired up (although it ran poorly).

    So is that the whole soloution do you think? Regap or replace both plugs and replace the battery?
  7. I bet it is jumping towards your earthing point ;)
    Blue spark, good sign. Your plug gap may be set wrong, but that is sedondary for now.
    Check the other side, I bet it's sparking too.

    Through all your push-starting etc. with no firing, I wouldnt mind betting the engine itself has a gut full of fuel in it. If it is a lot, it may have even seeped past the rings in to the sump. This will make your oil super thin (but generally wont stop it running) check the oil at some stage, at least before putting her back on the road permanently.

    After checking the other plug, I would be inclined to turn the fuel off, and wind it over (for no longer than 30 secs at a time, dont want to burn out the starter) 4 nor 5 times. You may get a surprise, and as the combustion chamber gets less saturated with fuel, it might spring to life even with the fuel off!

    If this doesnt work, let it sleep until tomorrow, giving the fuel time to evaporate and try the above.

    note- make sure you are not using any choke for thje next few wind-overs.
  8. Excellent!!
    For now, ignore the above post. I'll leave it there for future issues, if any other people have a similar problem :)

    Dad's know stuff, I am one :cool: :LOL:

    Yeah, I'd check and whack :rofl: the other plug too, and let it run for a while to purge any unspent fuel.

    Get a new battery for it, whack it in, and then there is one last step before we declare it safe for riding - the voltage test.
    Get back to us :)

    edit - yheah, definitely get new plugs too!
  9. Any more progress?

    From what you have said so far, I would start by cleaning and gapping the plugs correctly.

    If the plug gap was too wide the whacking technique may have helped but I am not sure that is the best way to gap a plug. Do it properly. Too small and the plug may foul. Too large and either no spark or the spark may be too weak to ignite the fuel mix.

    And you didn't mention it but are you using choke or not. A little choke may be necessary to start but crank it over for too long without starting and it may wet the plugs. Then choke is a bad thing.
  10. Awesome info joel. I know very little about electrics and will most likely revisit this thread at some stage.

    Very, very stupid question alert but could you jump start a car from a bike battery?
  11. You never know until you try. Try runing the bike and holding the revs above idle, see if it's enough power to get the car's starter motor going. If it's not then you have your answer.

    Just to give a little conclusion to this thread, I'm confident now that a new battery and properly gapped spark plugs will fix the bike and have it running again. I'm not going to do either of these things yet though because my friend who is the owner of the bike is going away on holidays and would prefer it done when she gets back.

    Anyhoo, thanks again for the help.

  12. you probally could but i guess the car would suck the power out of the battery very fast. much bigger starter motor depending on the car; if its a 4/6/8 but still drain the battery