I have a 49cc kaliber and put a performance pipe carburetor and a bore kit now it will bog down at 45 mph when it did 43 mph before?

Quite a few number of possibilities:

1) You're not getting enough fuel (your carburetor may need adjusted)

2) You're not getting enough air (your carburetor may need adjusted, you may need a performance air intake)

3) Your carburetor:

--float type

may not be able to keep enough gas in the fill bowl to keep up with the fuel need of the engine

--diaphragm type

same as with the float type, but the diaphragm cannot pump in enough fuel to the carburetor to keep up with the consumption of the engine

4) Could be a problem with your CDI if it has one. If it does, might want to look into upgrading to a racing CDI (and the speed\rpm governor\limiter might also be a part of the CDI which might be what is cutting you out when you go above 40-45mph)

Good Luck!

I can't give a definite answer but hopefully the above checks will help you out.