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This is very common with everyone that installs the HRC kit. This happens because of the cam that is included with the kit. Yes, most low end pipes will help this problem. You can ask the member desert_450r, because he has the kit and a CHM pipe and loves the performance. Something else that will help out may be a 13 tooth front sprocket because it will shorten the gears B)
I love my hrc kit, thats what i used (third gear) to clear a 90 foot tabletop. It dint seem to affect the first couple of gears much, but i think the power output is overall good for the price. but yes, i think you will be more happy with a pipe.