These are 2 concrete finishing machine engines. Both 4 stroke. Concrete business owner Michael Templin hopes for longer run times & more power to get the job done quicker. With less emissions, he is hoping for fewer headaches when using these machines in basements where there isn't much air flow to carry out the exhaust. I was able to use the medium bit for the Honda, but with the Subaru carb having the air/fuel cavity below where the groove is placed, i couldn't groove as deep.