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

http://wem.walbro.com/walbro/product...m=HDA%2D60%2D1

I could be wrong....but a HDA Carb may be a little to big for a 31cc ryobi????? Capt,n

11mm is about right. The membranes are the restricting factor. Trumpeting the entrance duct to the largest size the membrane petal will seal brings a substantial increase in power.

Pe R. Is that like a pirimid block of reed valves. Thanks Capt,n

I wonder if this is what is meant by:

“Trumpeting the entrance duct to the largest size the membrane petal will seal brings a substantial increase in power.”

tractor dude-you need a WT324,391 or 347 or I've heard but haven't seen 167. Except I've heard that some 167's have trumpeting membranes. Very noisy,I bet.