Coil problem?

[volks28]

I think I inherited a problem with my GS 850 83. When it's warmed up (after 15 minutes driving), it runs very badly / stalls

I narrowed the problem coming from the two cyl on the right side (small backfires come from that side). I used a timing light on those two cylinders and found one of them not firing right. I looked at the coil and looks ok, connections are good (no corrosion)

What should I attempt next? What tells the coil to fire on these bikes?

[bobo]

plugs ???h.g. :P

[redliner1973]

Pull them and tell us what you see......

[volks28]

Pull them and tell us what you see......

The color? gray with a brown tint and all 4's

New NGks to try to fix this issue. Old plugs where same color

[volks28]

Some more info on the coils

(when engine cold)

left coil
4.4 ohms across primary
10.13v at orange/white wire (between orange/white and battery ground)
21.57k ohms between plug wire

right coil
4.5 ohms across primary
11.20v at orange/white wire (between orange/white and battery ground)
320 kohms between plug wire (not sure why this is so high?)

Any ideas what I can troubleshoot? spark seem unconsistant on cyl 3 (assuming cylinder numbers go 1234 when sitting on the bike)

[SqDancerLynn1]

Try swapping the coil wires 2&3 or 1&4 to see if the problem moves to a different cyl

[redliner1973]

Voltage is too low at the coils. that is not helping at all...

[volks28]

2&3 are the middle ones right?

Do they fire at the same time?

Try swapping the coil wires 2&3 or 1&4 to see if the problem moves to a different cyl

[volks28]

Answered my own question using search :roll:

Thanks I'll check it out

2&3 are the middle ones right?

Do they fire at the same time?

Try swapping the coil wires 2&3 or 1&4 to see if the problem moves to a different cyl

[volks28]

Ok, I swapped 2 and 3 and problem followed the wire. There is a slight backfire on cyl 2 now. Again, the bike fired nicely when it was cold

:arrow: Can I run a +12v lead directly from the battery to the coil (just for a test?)

Thanks

[SqDancerLynn1]

Yes you can run the 12 v to the coil temp. If you check the coil voltage do it with the ignitor disconnected so there is no load. The readings that you got are way different between the coils. Try removing the spark plug caps (chech them), cut the wire back 1/4 " reconnect and remeasure the ohms

[Anonymous]

First, one coil fires 1/4 and the other 2/3. If doing troubleshooting, this must be kept in mind. Second, your voltage to the coils is low. This is pretty normal on an older bike. Voltage must go through the ignition switch (old/dirty), then the kill switch (old/dirty), plus a bunch of old wire and connectors (old/dirty). The sum of the old and dirty part is that less voltage gets to the coils than when they were new. See this link for a way to fix the problem: http://www.kzrider.com/ignition_upgrade.shtml
Now, to the coils themselves. The coil with the 320 K ohms secondary impedence has a short and will NOT operate properly. The other coil seems OK at about 25K ohm impedence (not sure what it should be for your bike but that is the right range). Coils get warm and over time, the insulation will melt and windings will touch. At that point, shorts will occur and operation of the coil will produce igntion misses which result in backfiring and erratic operation. I suggest you replace the coils with new Dyna coils. Contact Jeff Saunders at z1enterprises.com (he specializes in older bikes) as he has good prices on Dyna products.

[volks28]

I replaced the end caps and snipped the ends for cyl 2 and 3 and I get roughly 25kohm there too (thanks Lynn!) I also wired the 12v as per the link on the ignition wiring upgrade (great stuff!)

I now get alot of hesitation between 2000 and 5500. maybe I'm chasing more than one rabbit

Do I need to rejet now that the ignition system seem to operate correctly?

First, one coil fires 1/4 and the other 2/3. If doing troubleshooting, this must be kept in mind. Second, your voltage to the coils is low. This is pretty normal on an older bike. Voltage must go through the ignition switch (old/dirty), then the kill switch (old/dirty), plus a bunch of old wire and connectors (old/dirty). The sum of the old and dirty part is that less voltage gets to the coils than when they were new. See this link for a way to fix the problem: http://www.kzrider.com/ignition_upgrade.shtml
Now, to the coils themselves. The coil with the 320 K ohms secondary impedence has a short and will NOT operate properly. The other coil seems OK at about 25K ohm impedence (not sure what it should be for your bike but that is the right range). Coils get warm and over time, the insulation will melt and windings will touch. At that point, shorts will occur and operation of the coil will produce igntion misses which result in backfiring and erratic operation. I suggest you replace the coils with new Dyna coils. Contact Jeff Saunders at z1enterprises.com (he specializes in older bikes) as he has good prices on Dyna products.