Well the problem with these larger carbs is that they are designed to be used with larger bore engines so a small adjustment makes a big difference, this is even worse if you have not fitted a big bore kit to make it a 150cc.

First of all screw the idle mixture screw in all the way (clokwise) and make very small adjustments to get the idle right. If you are unable to get it right then you probably need a smaller idle jet. I had trouble finding one my self so I would suggest that you look at your current one then fine one on eBay that looks the same.

As for the needle position I have mine on the middle position but you might need yours set one position lower.

I have a 120 main jet which actually runs a tad rich. If you don't have a big bore kit installed you probably need a size 110.

Could you send a link to the carb that you have bought?