When Evel jumped over the cougar and snakes in 1965. He was using a Honda Elsinore. They were first made in 1974.
The BSA 441 Victor used at beginning of the movie wasn't available in 1958. They were made from about 1967 to 1972.
When Evel drops Linda off at home then drives down the street, cars used in the present day can be seen at the end if the street in stead of 1950 model cars.
In the scene set in 1950 Jerry Lee Lewis' recording of "Whole Lotta Shakin' Goin On" can be heard, seven years before it actually was recorded.
Several anachronisms include: Aluminum beer cans were not in use in the '50s; hardhats in the 50's were made of steel, not plastic as portrayed. The helmet worn during the Caesar's Palace jump was a modern helmet with extra padding around the face not yet available in 1968. During the skating scene, Knievel wore skates not available at the time.
At the Ideal Toys meeting, execs are looking at a prototype of a cube puzzle - clearly a Rubik's Cube. Although Ideal did look at a design by Larry Nichols for a puzzle similar to the Rubik's Cube, the Nichols design was 2x2x2, not 3x3x3 as shown in the film, and was eventually rejected by Ideal. The Rubik design was invented in 1974 and was bought by Ideal in the late-1970s.
During the Kings Island jump towards the end of the movie, the amusement park used as a backdrop is actually Cedar Point, located on the Lake Erie coast of Ohio. Not only is it the wrong park, but there are several coasters visible that were not even thought of when the jump occurred in 1975. Most notably Millennium Force which opened in 2000.