The inline-fours basically have two ignitions systems, so like Hardrockminer described, you can troubleshoot by swapping parts around. You can even do it with the pickups.
Pickups have been reported to become intermittent with heat in the past on Kzrider... not often, but it has happened.
After you rule out the coils, swapping pickups is a bit more involved.
On the pickup harness, you swap the black wire with yellow, and the blue wire with red.
That puts your ignition 180-degrees-out.
To compensate, you flip your advancer rotor 180 degrees.
Now if the problem moves to the 2-3 cylinders, you know the 1-4 pickup is bad (pickup with black wire and blue wire).
If that turns out bad, you can replace just the pickup, or you can even use a 2-3 pickup (red wire, yellow wire) in its place. You can use the same pickups from pretty much any inline-four Kz from that era. So there are quite a few options if you can't find your exact pickup plate for sale.