Wait, wait, wait... the engine on my kart has a GX140 head, which has a smaller exhaust port than a GX200 head & I used 1" tube which has an ID of 7/8"; using 3/4" pipe on a larger port will be restrictive &, therefore, defeat the purpose of "increasing performance"...
FYI: larger engines have larger exhaust headers, you may just need to redrill the stud holes...
Simply put, a straight pipe of any description will be loud, you will need a muffler of some description; for neighbourhood use, a "low tone" muffler is more desirable IMO...