no... that's why mechanics HATE "intermittent" problems - tracing can be VERY difficult!
e.g. bad coil scenario where one coil does two plugs...
coil is weak, so produces poor spark. in order to spark at all, it MUSt fire both plugs - BUT - bike is obviously now old, and so the two cylinders aren't identical - in fact one is burning a tad more oil than the other, or the carb is a little more out of whack, so a bit rich - and it quenches the spark so it doesn't DO anything useful on that cylinder, causing a misfire.
A combination of the two weaknesses is the symptom, but the REAL PROBLEM is the coil.
so my guesses in some resemblance of order...
dodgy coil, bad ht leads, plug caps, coil low tension wire ground(s) or power wires, plugs, dirty carbs/fuel supply problems
Change spark plugs, checking caps for cracks, pull the cap and cut a 1/4" off the wire and reinstall plug caps, try it, check/replace leads (they're old anyway

) check all undertank wiring, grounds etc.
If that hasn't got it, clean the carbs and fuel taps (again, probably due anyway). Failing that, you're into deep electrical trouble and in need of an expert.
good luck!
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Grant Johnson
Seek, and ye shall find.
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One world, Two wheels.
www.HorizonsUnlimited.com