Can't get 12 volts to both coils at the same time

[simon609zp]

If I measure the voltage from the orange and white wire at each coil back to the battery I get 12 volts. If I hook up the right coil (cylinders 3 and 4) the voltage on the left coil drops to about 8.5volts (measured at the pin inside the plug with coil disconnected). If I reverse the scenario and plug in the left side coil the voltage stays at 12v on the right side coil (again, measured at the pin inside the plug with the coil disconnected). I have tried to feed 12 volts to the left side coil from somewhere else and it does the same thing.

Needless to say the bike is only running on cylinders 3 and 4

What am I missing??

Thanks

[simon609zp]

Forgot to mention it's a 1982 GS850GL - completely stock and 36000 miles on it.

[posplayr]

sounds like two problems

First off

Left side is 2-3
Right side is 1-4

1.) 1-4 coils (Right hand) are working but there is a bunch of Resistance somewhere causing the coil load to drop your voltage to 8.5V.

2.) The 2-3 coils seem to be open and not pulling current so you never see the current drop.

[simon609zp]

Done some more troubleshooting. Plug both coils in and actually getting 9volts at both coils and also at the orange/white wire that connects to the igniter. Disconnect the igniter and the voltage jumps back up to 12volts.

I have measured resistance across both coils and they seem to be in spec

I'm thinking bad igniter.

Your thoughts . . .

[posplayr]

if you have excessive resistance in the ignition or start swicth then when the colis pull current (12V/3ohms = 4 amps per coil) then you will drop voltage across the switches and the coils will only see a portion.

If you have 9V at the coils sounds like the ignitor is working and you have bad connections. To check hot wire your orange white wires to the coils. If all is well clean your switches or do a coil relay mod.

[simon609zp]

I finally got to work on this thing again. Compression is right at 125 on all 4 cylinders, so I think I am all good there. Swapped the coils around and it still only runs on cylinders 3 and 4. The cylinders are numbered 1 to 4 , left to right, when you are sitting on the bike right??

[Matchless]

I finally got to work on this thing again. Compression is right at 125 on all 4 cylinders, so I think I am all good there. Swapped the coils around and it still only runs on cylinders 3 and 4. The cylinders are numbered 1 to 4 , left to right, when you are sitting on the bike right??

Just make sure you are getting spark on #1 and #2. You may be chasing the electrical side while it may actually be fuel problems. Usually #1 and #4 fire at the same time as does #2 and #3 so it already seems if your coils and plug leads are OK. Are the plugs OK?

[BassCliff]

Greetings and Salutations!!

Hi Mr. simon609zp,

Have you checked your plug caps and spark plugs? There more info in my "welcome thang"...

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