I've read just the opposite.
I've read where people have extended the stock manifold 3-4 inches, and they've gained low end torque.
I've been around and built drag cars, custom cars and motorcycles my whole life, and when i first heard that a longer intake will make more low end torque, i thought just the opposite.
Normally on an engine, longer, straighter intake runners kill bottom end torque but are great for high rpm's because they flow better.
but there have been a number of people who clain that they extended the intakes on these china 2 strokes, and they gained a bunch of low end torque and got better throttle response.