i have a 1980 jawa x25 that tops out at 23 mph, the bike runs good, the muffler is clean, new piston , and the timing is good, i just want it to be a little faster, say 30 or 35, anyone know of any mods i could do , i know there is a jawa x30, what are the differeces between the x25 and the x30?, thanks for any hep