1991 Other Hyundai Models Problem with engine

Hi ive owned my hyundai excel for about 3 years and its run reasonably well, however just recently I had a problem that when I would accelerate hard the engine would rev high and the car wouldnt go anywhere, I ended up fixing the problem with a new fuel filter and it seemed to be right but now I have a new problem. The problem happens occasionally when I have about a quarter of a tank of fuel the car stumbles on acceleration like im out of fuel or something. Usually it would never do this at a quarter of a tank of fuel. Im not sure if its spark or fuel related because I did have a faulty spark plug wire (the one that goes to the coil) and I ended up replacing the whole lot. One other question I have is how do I adjust the handbrake on this car ive tryed the handbrake adjuster nut on the back of the handbrake but it didnt work, the car still rolls forward with the handbrake on. The back brakes are drums if that makes any difference?Thanks any help would be awesome.