If you mean hp/lbs then I think its in the neighborhood of 27hp/400 lbs for the SOHC. That'd make it 0.0675 hp/lb or 0.1485hp/kg. Even making small adjustments can alter your ratio very significantly.
I guess in order to feel like your accelerating with one more horsepower, you'd have to decrease your weight by about 7 kilos or 15 lbs. If you've removed 48lbs, you're probably going to see the equivalent of a 3hp increase.