Jimmy offers to his dad to "regrind the valves" on the lawnmower's engine which they intend to put in the go-kart, but judging by the noise and smoke it gives off it must be a two-stroke motor which would not therefore have any valves to regrind.
The opening scene with the soapbox racing down West Street is filmed in several takes to give the impression that the street is longer than it really is.