Those pipes are designed for 22.5-26cc Zenoahs, Quickdraw, J&G and etc engines at up to 20k rpm loaded. The 2hp Jiffy is 49cc and needs a pipe for it displacement and operating rpm range. Maybe a pipe for a similar displacement Goped engine, I need to look into it further.
I agree if you touch the exhaust side with a pipe or even a decent muffler the carb has to be dealt with because on the later 2hp engines they are fixed needle carbs.