Yes. at least the ones that I have were. They both had a #54 stamped on the inside. I have 2 Mag20s and a Mag18.
Although, the needle seat is not replaceable in those carbs, so the needle still leaked on mine. I swapped to a #26 Kohler carb. Because the #26 came off a single cylinder, I had to swap over the butterfly linkages.
Thread appears to be about Mag18/Mag20 carbs but the title is need to repower my 982??? According to my 1872/2072 owners manual, it appears that the 1872 (mag18) could come with a Kohler carb that has both low speed and high speed screws. I found one on a mag18 and rebuilt it using the standard Kohler kit for a #30 single carb. This Carb even had replaceable seat. The 2072 (mag20) is supposed to have a walbro carb with only a low speed screw. Looking at the carb from the Mag series, it appears you could substitute a #26 or #30 carb on these engines if you changed out the bufferfly shaft from a Mag carb. Anybody ever done this? Nic? Big Steve?
do the KT carb rebuild kits use the standard single cylinder Kohler rebuild kits that cost around 12 dollars? I priced one rebuild kit for a mag engine and the cub dealer told me 54dollars!!!! I would probably buy one of those knockoff china carbs on the interweb before rebuilding one of those....