I've ran that 125 with a 48" on an 8 pin .404 .Fact I have to on the 2100S Homelite because that's the only configuration it came in .Keep in mind the Homey is 114 CC and the Mac is 123.
Depends on how the 101 Kart engine was ported.They did them according to what they raced .Short track,long track,road course .I'd guess if it was a short tracker it probably was high ported for RPM and big carb or not it probably would not have the low end torque as a stock 125 .On an oval,long or short you wanted them to hit max RPM about the time you hit the brakes going into a turn .They did that ,long short,with the gearing .Road course they were ported for mid range because more times than not the course didn't have enough straight track to hit max RPM
I've tried the 125 with an 8 pin 3/8" and it did not cut as fast as using .404 chain .Conversely on a 250 I found a NOS Oregon 3/8" .050 18" which BTW takes a 72 driver chain .With an 8 pin it did cut faster .Neither one of them are racers though .Just old torquers .