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Can "half" of a coil go bad?

H

hannibal

Forum Mentor
I've been trying to get my bike running but cylinders 1 and 2 remain cold. I thought this couldn't be a coil problem because I tested them by grounding an old spark plug to the head and saw a spark. Then I read that coils can test good when cold, but not fire once they've warmed up.

Have you ever seen a case where one of the coil outputs works while the other doesn't? For instance, can the 1-4 coil fire properly on the HT lead to cyl 4 but not fire the lead to cyl 1? I plan to swap the leads between 1 and 4 to see if the dead cylinder follows but just wondering if this issue is likely or even possibly.
 
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Not sure, but have you checked the spark plug wires and wire/cap connection? I had a bad spark plug cap on mine- corrosion and a bad in-cap resistor.
 
hannibal said:
I've been trying to get my bike running but cylinders 1 and 2 remain cold. I thought this couldn't be a coil problem because I tested them by grounding an old spark plug to the head and saw a spark. Then I read that coils can test good when cold, but not fire once they've warmed up.

Have you ever seen a case where one of the coil outputs works while the other doesn't? For instance, can the 1-4 coil fire properly on the HT lead to cyl 4 but not fire the lead to cyl 1? I plan to swap the leads between 1 and 4 to see if the dead cylinder follows but just wondering if this issue is likely or even possibly.
Click to expand...

Not possible IMO. The twin lead coils spark path is one lead, coil to ground, then ground to second lead to coil....If you've got a spark on one side you've got a spark on both.
Be aware though that one side can be through a leaky lead rather than the plug...

Most likely to be a fuelling issue IMO.
 
Thanks for the replies. I trimmed a bit off the end of each HT lead, but haven't rechecked resistance. Visually the wire ends look 10 times better.

I'm redoing the carb cleaning process. I think it's a carb/fuel issue as well but wanted to rule a coil problem. Thanks again.
 
I've had dyna 3.0 ohm coils drop one side. it is possible. I even swapped the coils from my kz to my gs, used different wires with the coils, and still had one bad side on that coil. so again it's possible, just highly unlikely. but then again, I'm usually blessed with those oddball issues.
 
Id be more inclined to look for plugged pilot jets this time of year if you didn't run the carbs dry. Stabil doesn't work for me on the 4 cylinders , the pilot jets are too small but I would ohm out the plug leads and caps first
 
If it's the carbs then the bike will fire on the non-firing cylinders when you rev it because it's highly unlikely you have blocked main jets.

Do the lead swap between 1-4, 2-3 and see what happens.
 
I had a Dyna go bad on one side.... The contact between coil & wire came loose & then it basically spark eroded the contact away until it didn't work any more. Dyna replaced it.

With the stock I can't imagine that happening as the wires go onto 3/4" long pointy stick at that end.... more likely to be a break in the wire or a faulty cap in that case.

:)
 
I'm trying to sync the carbs and i can't get the bike to rev more than 2500-3000 rpm. I'm gonna check primary and secondary resistance. Giving the carbs 3 days in the carb dip and paying extra attention to cleaning the pilot circuits.
 
24hrs is sufficient for a dip. 3 days can darken the metal. if darkening the metal don't bother you, then go for it
 
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