That carb is no longer available from Walbro. The venturi is 13.49mm and the intake should have a cast number of 34 which means the intake is 34/64ths of an inch in diameter. Seems a little large for your engine. For the many 44 and 50cc engines I have done I used a WT-201 which has a 13.4mm venturi. I would be looking for a carb in the 10 to 12mm size. On engines that size I have done I have used 11.11 mm carbs with great success.

Just looked at my 61cc Echo twin and I used the WT-201 on it as well.