It’s an American movie from the 1980’s, was on HBO or Showtime, and done in the style of Better off Dead.
A younger man sends off for something from a comic book i think by saving up cereal box-tops or something. He ends up either not getting what he ordered and sets off for the mail order company.
The 2 parts I remember are that he puts an engine in a soap-box-derby car to win a race and at some point he cut’s a gas-station signal hose into pieces and plays music on it. He trades a baseball card and some other things for a replacement toy engine for the car, he also has to pay at a gas station to re inflate his tires which bothers him slightly and ends up filling up several plastic bags full of air since he had to pay for it, later in the movie a car that has been a nuisance to him is tricked into going in a parking lot through the exit and it has those odd spikes that flaten tire if you drive in through the out. and he ends up giving the driver his bags of air. That all I remember of the movie. I hope someone else has seen it and can remember the title.