Most people cheat the gas pedal pot calibration to make the game easier. The game is designed to give flames/boost for a few secs at full throttle in HI gear but it has a bog down effect that kicks in if left on full throttle into advoid this game feature they rotate the pot to advoid the full throttle bogging down/engine under powered effect.
@fatherpain is absolutely correct. You have to be able to feather/modulate the gas pedal once you shift from LOW to HI gear in order to play the game properly.
Also, the game will not let the car to move from a dead stop unless you are in LOW gear. Most players die a lot from crashing while driving too fast. Restarts happen frequently so having LOW gear selectable is a must.
And there are times when you want to drive in LOW gear full time and there is gas pedal modulation required in this mode as well during the water phase of the game.
I'm all for Jamma alternative to keep these games alive but Spy Hunters controls are very unique and specific to this game.