Loss of 2 cylinders & tacho!

[SHEPPO]

G'day all,

Last sunday was out on a ride with the bandit (1990mdl 250) and with no prior warning i lost 2 cyls and the tacho. after a quick check over the ignition wiring we jiggled the coil pack terminals on the left coil and then she fired up and i've had no drama's all week (i ride the bike daily to work).

firstly, how are the coils wired? i cant find a wiring diagram for the bike anywhere, so its guess work at the moment. what coil does the tacho get its reading from? i am assuming the left hand coil?

secondly, the bike has a noticable miss when fast idling on choke, is this normal? the bike runs cleanly and makes good power thru the revs when its running along, and once warm i sit the idle at 2000rpm and it sounds fine. i am thinking maybe change the plugs?

any help on these matters would be appreciated. i have a high level of mechanical ability (mech engineer) and good with electrics.

thanks

Dave.

[stormi]

G'day all,

G'day, and welcome!! :)

Last sunday was out on a ride with the bandit (1990mdl 250) and with no prior warning i lost 2 cyls and the tacho. after a quick check over the ignition wiring we jiggled the coil pack terminals on the left coil and then she fired up and i've had no drama's all week (i ride the bike daily to work).

Let me guess, the two middle cylinders?  2 + 3?

firstly, how are the coils wired? i cant find a wiring diagram for the bike anywhere, so its guess work at the moment. what coil does the tacho get its reading from? i am assuming the left hand coil?

Correct, (as long as this is the same as the B4 setup, and I suspect it is) The left coil controls the two middle cylinders, and the right controls the two outside cylinders ( 1+4).  In addition to the left coil's sparking duties, the low voltage wire leading to it also feeds info to the tach.  So, typically, if you can "jiggle the handle" and it works, you likely have a broken wire leading to the left coil.

secondly, the bike has a noticable miss when fast idling on choke, is this normal? the bike runs cleanly and makes good power thru the revs when its running along, and once warm i sit the idle at 2000rpm and it sounds fine. i am thinking maybe change the plugs?

I'm not sure how a 250 should run, but it never hurts to check ( to see what story they want to tell you - i.e. rich, lean, too hot, too cool, etc), and change the plugs, and while you're at it, since you'll have the tank off anyway, trim those spark plug wires to get rid of any corrosion that could be affecting spark.  

Which cylinder seems to be misfiring?  You can tell that with a hand to the headers shortly after it's started ( before they heat each other up too much to tell) and you may be able to tell with the plugs.  

any help on these matters would be appreciated. i have a high level of mechanical ability (mech engineer) and good with electrics.

thanks

Dave.

I hope some of this helps,.. also, here's a link to one of our regulars having the same problem with his B4:

http://forums.banditalley.net/viewtopic.php?t=8845&highlight=coil+tach

edit:

Oh! btw, I noticed two SHEPPO IDs in the admin panel registered at the same time.  I activated the one you're using.  Did you mean to register twice?  Shall I delete the other?

[SHEPPO]

yeah that was probably me, the activation page was saying the email was already used by a forum member or somthing.. even tho i've had that particular email address for the better part of 5 years, hahaha..

the missfire on choke isnt a great concern to me at the moment, as the bike runs fine once warm. i will however look at the plugs tho and change them whilst i'm at it.

thanks