Help with an electrical issue

hey guys.

i feel like i need to ask for help here because i am getting really frustrated. its about a kz750 ltd 1981.

couple days ago while driving around out of nowhere the engine started to backfire and run only on 2-3 cyl. i stopped to check if the cable from the coil was lose because that happened a few times but it didnt seem to be the issue. i pulled out the cable from the right #4 spark and it seemed to be the cylinder affected. when i pulled out the #1 spark cable the spark jumped from the cable to the engine and back to be and i got a good shock. when i arrived home i got another shock just by touching the carburator.

i started to rule out a couple things. it is not:

carb
spark plugs
spark cables
coils

the weird thing is that it comes and goes. typically it would start with 4cyl and within seconds it goes down to 2-3 cylinders (i have problems telling for sure if its 2 or 3 by the sound). when i apply full throttle and get over about 3.000 - 4.000rpm it would run on 4 cylinders but still sounds like its not running well. i guess the best way to describe is as if the battery is really low and it doesnt have enough power to spark. battery is fully charged though. just charged it again over night and its new as well.

so basically as far as i know there are only 2 things left. one of the plus cables are bad, which i checked but maybe i was missing something or the pickup coils. but from my experience they either work or are dead and smell burned. any ideas? thank you!

Plugs can be bad. If you got a shock from #1, four is fowled. Get new plugs first. Cheap and good for spares. Like to see a pic.
Steve

Let's start with known good items:
1. New sparkplugs(try Denso, instead of NGK).
2.New sparkplug caps(they have a 5000 ohm resistor, that goes bad from heat, vibration, and age)
The old ones are screwed onto the sparkplug wires. www.z1enterprises.com sells new ones, and most can be bought at a local Japanese motorcycle shop.
Try these steps, before buying other items/adjusting the carbs.

If you've never cleaned the many and various electrical connectors and handlebar switches, they're probably way overdue. www.deoxit.com is the website for a very good electrical contact cleaner/preservative I use.

The factory soldering jobs were iffy at best, and they are starting to fail on the older bikes. You'll need to open up the left and right handlebar switch "Pods", to access the electrical switches and contacts. I recommend no more than a 25 watt soldering iron be used to repair the bad solder joints, as the insulation on the wires may melt, and other hear sensitive items may be damaged, with higher wattage soldering tools.

The sparks plugs are brandnew (yesterday) the ones before only 3 weeks old and the caps are also still as new. Only 2-3 months old.

Yes, #4 was a little foul, seems like the last time I cleaned the carb before I coulnt turn the idle screw all the way back in. I fixed that already and the sparks are new but its not the issue im having right now.

I dont have any switches on the handlebar or any gauges. I had a similar issue when cables from the battery were lose but i checked that, cleaned it and even installed new connectors in the cables 2 days ago, trying to rule out locations.

Oh and also every single cable is new. I installed all cables from scratch again couple months ago because before it was a mess. I still suspect one of those cables might gone bad or is not connected correctly anymore or bad from overheating. I guess I have to open it up complete again and check every single cable coming from the battery to the coils etc.

Could it be the caps? Really doubt it after a few months only. They look like in perfect condition inside and outside and I removed them one by one and used them on another coil with other cables as well.

Have you checked the center electrode of the sparklplugs? Black is too rich, White too lean, but a nice light tan color is about right. Airfilter(s) clean and not clogged? Fuel filter in good shape? No restrictions in the fuel lines? Are you using any of the Ethanol Gasoline? If so, try to find a brand that does not have any Ethanol in it.

yes the sparks are perfect since months except for the #4 last time i cleaned the carbs but thats fixed and new sparks are installed. i change sparks pretty much monthly. airfilter is currently even off while im checking for the issue. fuel filter 1 week old. its no fuel issue. its def. electrical. i never get gas at one of those ethanol gas stations. only quality gas stations.

im about to go crazy. still can't find the issue. randomly jumps from 4cyl to 3 or 2, in high rpm, full throttle i get it back up to 4. i replaced the coils again just to be double sure, first turned on on 4, already thought i found it even though i was sure its not the coils, just to see that a minute later it will drop down to 2 and 3 cyl and turn off. i checked/replaced all kind of cables including spark plug cables, not the caps but they are as new still. it simply can't be that. no corrosion whatsoever inside and just a few months old.

could it be the pickup coils? but it doesnt make any sense. they usually either work or burn through and it would run on 2 cyl, not on 3. yesterday i swapped the plug from #4 to #1 and the other way around and it sounded different and i saw fire coming out of the exhaust pretty much constantly. so i am confused again, could it be the almost new caps?

what could possibly break inside the cap? the connections look new when i look inside it.

turns out it was the caps. unbelievable.. they were only 3-4 months old the max. i wonder why they broke. driving in the rain? heat? using powerful access coils? weird.. but thank you for everybody who tried to help!

Hey guys. I sadly have to move this one up again. I have another question. I installed the new spark plug caps which fixed the problem and only one day later one cylinder started backfiring and randomly work or not, so one of the caps is bad again.

HOW can this be possible? I already changed all spark plugs and its the cap again. Could it be one coil is bad and messing up the caps or how could it be? Again, Im using Accel coils not stock. Do I need to use different cables and caps for that?

Thank you very much