some people are just not very handy. a good example would be my neighbor accross the street. he replaced the carb on his snowblower. he got it to run but the throttle wasn't working and it sound like he had the throttle set too high. i took a look at it and found this. while he was installing the carb he bent one of the rods so the throttle lever did nothing and it was running at the rpm he set it to with the idle speed screw. he got lucky because i think he did have the engine running at 4000rpm. i replaced the rod and adjusted the carb to where it should be and had it all working like it should again.#2 reason is they don't have enough confidence to try and do it themselves.