Our yerfdog has been turned into a trike,and a beefy one at that! So we aren't using the factory linkage bars from it, instead we have a cable throttle from the handgrip to the engine. We cut it up partially because the frame looked like a car t-boned it, and there was lot of neglect and shotty repairs. You should be able to back out the throttle screw on that engine allowing for full throttle, back it out as far as you need/want and it should help.
