Yes, it probably is.. But before you spend a lot of money, just check the obvious spark killers.
Assuming correct point gap and timing, These are (as others have pointed out);
Dirty points. Singles can blow a little oil through the Magdyno and out via the points cover. I have had a bike with exactly your bike's symptoms due to this.
Crap on the HT pickup - clean the pickup and the brass ring in the magneto.
Any kind on suppressor stuff - lead, cap, plug.
Broken HT lead (stranger things have happened). I had an intermittent problem in a car which turned out to be a broken wire inside the sheath.
HT lead earthing against the motor.
'51,'56 Squares, '48 VH, '27 Model C, R67/2, Mk IV Le Mans, '06 Super Duke and Ariel projects.