Dead cylinder. When I unplug the good cylinder plug I get shocked.

Sudonate91

Sudonate91

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So this just started. I felt half my power so I check my ignition. Bike would run when I pull my left side - die when I pulled my right (and kept my left). I tried to see if I had spark and I can't seem to see one. I switched plug wires and the left cylinder seems to still be the problematic one. Weird thing is when I let it run, then unplug the right cylinder. I will feel a shock if I'm touching metal. So that tells me my left plug has a bad ground thus no spark? If I give her gas then unplug my right it will stay on - only at idle.does it die.

Any thoughts?
 
When I take the plug out. And put it on the block and start I see no spark. But when I get it really close it will spark without touching. The spark will not be inside the gap
 
I'm not sure about the getting shocked thing as I never mess with that "dead cylinder" stuff. But I will ask you, are your plug caps the originals? If so, they can go bad, their resistance starts climbing and eventually it starts choking off the spark. Remove the cap (it just screws off) and measure the resistance through it. Stock (and good) is 8K to 9K ohms. If you measure, say, 10K ohms or more, that cap is going bad. The usual replacement is a 5K ohm NGK cap. It's also possible the connection between the cap and wire was bad, corroded maybe. Clip 1/4" to 3/8" off the end of the wire to get to some fresh wire before screwing the cap back on. I also like to strip off another 1/8" or so of the insulation and fan the wire strands out in a radial pattern like so .....

Plug Wire End.jpg


This insures the cap will make a good connection when you "screw" it back on.
 
5twins said:
I'm not sure about the getting shocked thing as I never mess with that "dead cylinder" stuff. But I will ask you, are your plug caps the originals? If so, they can go bad, their resistance starts climbing and eventually it starts choking off the spark. Remove the cap (it just screws off) and measure the resistance through it. Stock (and good) is 8K to 9K ohms. If you measure, say, 10K ohms or more, that cap is going bad. The usual replacement is a 5K ohm NGK cap. It's also possible the connection between the cap and wire was bad, corroded maybe. Clip 1/4" to 3/8" off the end of the wire to get to some fresh wire before screwing the cap back on. I also like to strip off another 1/8" or so of the insulation and fan the wire strands out in a radial pattern like so .....

View attachment 213464

This insures the cap will make a good connection when you "screw" it
Click to expand...
The original caps and wires. It's bizarre to me that it will run on the left cylinder under throttle. If I unplug the good plug while under throttle it will stay on and if i touch any metal on the bike I can feel the zapping of the spark.
 
5twins said:
I'm not sure about the getting shocked thing as I never mess with that "dead cylinder" stuff. But I will ask you, are your plug caps the originals? If so, they can go bad, their resistance starts climbing and eventually it starts choking off the spark. Remove the cap (it just screws off) and measure the resistance through it. Stock (and good) is 8K to 9K ohms. If you measure, say, 10K ohms or more, that cap is going bad. The usual replacement is a 5K ohm NGK cap. It's also possible the connection between the cap and wire was bad, corroded maybe. Clip 1/4" to 3/8" off the end of the wire to get to some fresh wire before screwing the cap back on. I also like to strip off another 1/8" or so of the insulation and fan the wire strands out in a radial pattern like so .....

View attachment 213464

This insures the cap will make a good connection when you "screw" it back on.
Click to expand...
I get 5.5k ohms on both caps. Also interesting. The good plug cap was actually barely hanging on!
 
Higher RPMs means more voltage is being generated and fed to the coils, and that may be enough to push through that higher resistance in the plug cap. Also, you may be suffering from a common old bike problem - low voltage to the coils. You start out with 12 volts (or better) at the battery but by the time it goes through all the switches (ignition, kill) and connectors, you may not get 12 volts at the coils, especially if there's corrosion in those things. Test the voltage on the R/W wires feeding your coils. If it's 11 or less, time to clean all the switches and wiring connectors.
 
5twins said:
Higher RPMs means more voltage is being generated and fed to the coils, and that may be enough to push through that higher resistance in the plug cap. Also, you may be suffering from a common old bike problem - low voltage to the coils. You start out with 12 volts (or better) at the battery but by the time it goes through all the switches (ignition, kill) and connectors, you may not get 12 volts at the coils, especially if there's corrosion in those things. Test the voltage on the R/W wires feeding your coils. If it's 11 or less, time to clean all the switches and wiring connectors.
Click to expand...
I replaced the entire wiring loom and it had a new battery. I'll start pulling voltages everywhere else once I get some time. The caps are showing 5.5k ohms. I also made sure they were screwed snuggling now. Still problematic.
 
Now I'm very confused. I was able to ride it home with no issues. So either the right plug wire being loose was the issue (which was opposite to my issues) or me pulling and plugging things a bunch fixed it
 
Last edited:
Sometimes that's all it takes. You've "refreshed" the connections by unplugging and plugging them back together. Something else to look at is the plug wire connection at the coil. That may need to be redone too.
 
What ignition is this?
If it's dual tower coil do NOT pull wire off a plug while running. Overall pulling sparkplug wires off sparkplugs on running engines isn't a good idea for several of reasons. Look for a plug wire getting pinched between gas tank and top of motor, it's common.
 
gggGary said:
What ignition is this?
If it's dual tower coil do NOT pull wire off a plug while running. Overall pulling sparkplug wires off sparkplugs on running engines isn't a good idea for several of reasons. Look for a plug wire getting pinched between gas tank and top of motor, it's common.
Click to expand...
Dumb question. How do I tell why type of coil it is? Mine is like a cylinder/drum with 2 wires coming out of it. Doesn't seem like it they can be unplugged from the coil either.
 
That would be a TCI type electronic ignition or other aftermarket electronic ignition. The coil fires both spark plugs at once you need to have a grounded spark plug on BOTH sparkplug caps any time the igniton is on, motor turning.
In this picture the RH side you can see how the secondary must jump the gap on BOTH plugs to work properly.

dual tower coil.jpg

My guess is there is a pinched area or other path to ground on the LH side why the right was fine and there were sparks when you removed the RH wire; cuz the voltage HAS to find a path to ground. I have a nasty story about high voltage and a rain storm on an XS650.
 
gggGary said:
That would be a TCI type electronic ignition or other aftermarket electronic ignition. The coil fires both spark plugs at once you need to have a grounded spark plug on BOTH sparkplug caps any time the igniton is on, motor turning.
In this picture the RH side you can see how the secondary must jump the gap on BOTH plugs to work properly.

View attachment 213483
My guess is there is a pinched area or other path to ground on the LH side why the right was fine and there were sparks when you removed the RH wire; cuz the voltage HAS to find a path to ground. I have a nasty story about high voltage and a rain storm on an XS650.
Click to expand...
It's the stock TCI. So that makes sense on why both need to be grounded to start the bike and get it running. But after that I can unplug 1 and it will continue running? But only one. When I unplug the left plug it will continue. The right it will die unless it's under throttle.
 
To repeat
My guess is there is a pinched area or other path to ground on the LH side, why the right was fine and there were sparks when you removed the RH wire; cuz the voltage HAS to find a path to ground. I have a nasty story about high voltage and a rain storm on an XS650.
 

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