Just a word of thanks to others on this forum for your advice and info. I bought a 2012 S40 a few months ago, and have already applied some of the suggested mods. Progressive Suspension rear shocks have improved the harsh, jolting ride and adjusting the idle mix screw has improved the sporadic gunfire (backfiring). So I recently located and purchased an OEM Yamaha Raptor 660 petcock, anticipating failure of the stock unit someday. 1049 miles, and guess what happened yesterday? The tank was over half full, the motor conked out, tried reserve, no luck. Pulled off, switched to PRI, and got me home. With the advice here, the change was not difficult, and the new petcock fits perfectly. I guess the Versalavy (sp?) is next.