I've heard if you mix equal parts auto tranny fluid, diesel fuel, turpentine and acetone that you can make a pretty great penetrant to loosen up stubborn bolts.
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It could also be something as simple as the linkage from the throttle to the carb sticking. I use to have to put my foot under the throttle and pull back on the pedal with my foot to bring the idle back down on my old 76 Cruiser. The linkage always got hung up in one particular spot and a quick...