Why did the 80/85 shifters die off? Part of it might be when shifters took off nationally. Before that there were Senior-class 80s on the regional and club level all over. But when shifters hit the national level, it eventually morphed into: Senior class race 125s, Juniors race 80. That perception seemed to trickle down to local level afterwards.
But probably the biggest reason for their disappearance? TaG. It offered about the same power as an 80, but in a ready-made package specifically for karting. The club racers that would have raced an 80 shifter gravitated over to TaGs, eventually the 80cc Juniors at the national level did as well, until most of the 80s were gone, except for a few diehard areas like NorCal, and MSOKC in Ohio.
And I’ll never understand why they fell out of favor either. Let’s face it, many of us would have a much better time racing an 80 shifter than getting overwhelmed in a breakneck 125. And they’re a much more appropriate vehicle for a newbie driver looking for a shifter kart experience and are dead set on that only. Everyone I’ve read discuss it mention how the 80 engines’ smaller size is a better fit for a kart. Best reason of all, their lower HP levels and subsequent top speeds mean that a front-brake chassis isn’t required, whereas in a 125 it’s mandatory.
It doesn’t take a genius to know that the lower entry costs from a rear-brake only chassis would make the class a lot more appealing to some.