make sure all valve body mounting bolts are properly tightened,if bolts are ok there is a small allen head adjustment on the right front of the valve body.
turn this screw out,but don't start with large adjustments maybe 1/4 turn at a time.if you go too far the r.p.m. limiter come into play.
these adjustment should only be performed after checking condition of cable and it's adjustment.
m.f.