Hi, i recently purchases a 1978 Columbia Commuter with the 505 Sachs engine. I've rebuild and cleaned the carb and replaced the spark plug. Everything else seems to be in good running order. The moped tops out at 25 on flats and really bogs going up hills. I stalled it trying to go up a steep road. I've read tons of stuff on performance parts and derestricting mopeds in general but can't seem to come up with any good ideas for my moped that don't involve expensive new parts. Anyone out there know any adjustments or things to check that may need maintenancing?