the bigger the cam the heavier the springs.....
No, Not realy. But normally stock valve springs are longer than a stiffer performance spring. So a big cam with stock springs is not good because you can run into a probelem called "Coil bind" Where the cam tries to compress the spring more than it can be compressed which causes damage. Normally a performance spring is shorter and has less "coils" For example here is a 18 LB spring VS a 26 LB spring.
http://www.affordablegokarts.com/mm...e=A&Product_Code=HON14751&Category_Code=GGPP5
http://www.affordablegokarts.com/mm...de=A&Product_Code=VS26LBS&Category_Code=GGPP5