150cc tao tao carb upgrade too big -

[4getful2]

I don't see anything wrong with what you're doing as long as the intake manifold-runner isn't too long.
Same goes for the air filter pickup,Try running it up front or if you're deleting the bucket all together, you could use that area for an air pickup. Out the back, you'd probably pick up too much dust.
You may have to play with your needle adjustment a bit.