....also make sure that when you put the throttle assy on to the bar that you leave enough gap in between the grip and the bar. To do this, slide the throttle assy on to the handlebars till the bar hits the throttle tube/grip, then back it out a little but not too far to establish the gap-maybe about 1/8" (you won't be able to measure it but gives you a feel off how far to go), then tighten the throttle assy bolts as appropiate.
Also verify that your throttle cable is routed correctly on the bike-may need to reference a service manual (which you should have!) to see the proper routing...beileve me it does make a difference.
Hope this helps.