i am converting a 31cc ryobi for my supersportster and i found a walbro carb that is 15mm on one side and where the choke is its 18mm. how can i find out what model it is?? on the choke its stamped 62-40 and on the top 21-245-5-4 on the side were the high and low needels are HDA 60 k1. will it make a big difference in rpms to go to a bigger carb? thanks john