Subaru E10 Columbuss having trouble reaching high RPM

Transcript: (Movie starts in the drivers-seat, with engine off.) -OK, so this is the Subaru E10, trying to rev up. OK, it's been running for a while now, so it's 'bout quarter way warm. (Refering to where the engine temp.gauge is, on the dashboard). -OK, starting now. (Turns key. Engine starts). -And then, we go back to the engine here.(Moves to the rear of the vehicle). -As you can see, it's running pretty smooth now on idle. But when I try reving it up... (Reaches for throttle valve. Engine revs up, but starts to splutter and afterfire on full throttle.) -...it just doesn't seem to do it. Anyone got a good idea? -By the way, I'm gonna show you guys how it looks like. (Moves back and pans the whole car.) -It's quite cute, isn't it? -OK... Sugguestions, anyone? (End of movie.)