i have an 87 daelim trac olympic with a 15mm aha 68 jet. tops out at about 30-32mph but would like to go about 40. low end picks up really slow. i literally have to push it to get it going. the sprocket setup i have now is 12 in front 42 in rear. front sprocket is welded on so nothing i can do there. anything i can do to increase low end?