I’ve experienced the same sorts of issues on other people’s karts with the pump around. Not sure how to get around it. One unorthodox solution, which I use on my kart is to install a mikuni 1.8mm float needle seat(from, I think a VM34/39) to deal with the fuel pump pressure, and a boyesen “super bowl” to deal with the sticky float issue.
http://www.amazon.com/Boyesen-Super-Bowl-Float-Keihin/dp/B0050HIXTS
I bought the kart this way and I haven’t had a single non user induced problem out of it.
