Even bad plugs should do something, unless they are totally shot.
Did you renew the HT leads, and disassemble the caps?
Make sure you disassemble the caps, and clean them, and yes the caps get cruddy.
Here my write-up,
Quote:
Short explanation: The inside of the hard plastic caps accumulate crud the can short out the spark. This can cause rough running or failure to start. Every time you do any work on the bike: remove them disassemble and clean them and renew the wires or at least the connections.
The long Explanation, Warning engineering information can cause Drowsiness.
The ancient cylinder design of the engine dictates that the spark emanate form the center of the combustion chamber. In order to get it there, the plugs had to be located down deep in a well between the cams. This well is a perfect place for dirt and moisture to accumulate. Then because there is no cooling water at this point the metal around the plug runs very hot. Surround this with the large amount of cool metal and you have a recipe for condensation. Now K did drill a drain hole between the fins to help (a little) but it often gets plugged up.
The moisture boils off the base of the plug and the vapor condenses on the cool plastic cap and the plug insulator. This moisture forms a easier path for the electrons to ground than jumping the gap at the plug to make a spark. Misfire.
This issue is right up there with Pilot jets as a cause of trouble.
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Here's some pictures that might be helpful. I took these when I replaced the wires themselves, as it was a good time for a write-up, and the wires were OEM from 1998.
Wires are just 7mm copper core, with clear silicone jacket
NGK Iridium IX® plugs are the way to go personally, I run them in both the Ninjette and EX.
http://www.ngksparkplugs.com/product.../iridiumix.asp
NGK (7669) CR8HIX Iridium IX Spark Plug, Pack of 1
https://www.amazon.com/dp/B000HDF852..._3P6Zvb2PBX9FX
You need three things for the engine to run, fuel, spark, air, all in the right amounts, and timing.
An engine is just an air pump when you break it down to the basics.
Sounds like your petcock might be bad? How did you clean the carburetors?