1974 Valiant Scamp, timing retarding when revved

If it runs, the box is still good.I've seen them die, but never while running. It's just one day you will go out to start it and doh, no sparky. I've had one like yours run for years still, but I always carried a known-to-be-good,spare. I've also seen quite a few like yours and worse, still running. I figured that junk must just be a water proofer.If you replace it with a new one, throw this one in the gbox for a spare; it might last longer than the new junk.