Absolutely nothing ! I waited a long long time to get a WYK 16 and found out it's not available in this country, Walbro couldn't even get one from Japan. I am still using the WYK 61, it works real good, I have no complaints really. I have the low end set pretty rich for easy starting and a very low phutta phutta idle, if it was leaned a bit, I wouldn't have that sagging while inverted, but for my application, the killer idle is more important. I think this Carb might be a bit too big for the 25, I'd love to try a new cam, but I haven't found one, This carb might be perfect on a 31.