acceleration problem

document.addEventListener('keydown',function Down(e) {
        e.preventDefault();
        if(e.keyCode == 37){
            //left
                    e.preventDefault();
            goLeftVar = setInterval(function GoLeft(){if(-3<drawX){ClearAndDraw();
            drawX = drawX - VelocityOfJetVarTWO;}/*left*/},VelocityOfJet);
        }
        if(e.keyCode == 38){
            //up
                    e.preventDefault();
            goUpVar = setInterval(function GoUp(){if(drawY>-1){ClearAndDraw();
            drawY = drawY - VelocityOfJetVarTWO;}/*Up*/},VelocityOfJet);
        }

        if(e.keyCode == 39){
            //right
                    e.preventDefault();
            goRightVar = setInterval(function GoRight(){if(701 > drawX){ClearAndDraw();
            drawX = drawX + VelocityOfJetVarTWO;}/*right*/},VelocityOfJet);
        }

        if(e.keyCode == 40){
            //down
                    e.preventDefault();
            goDownVar = setInterval(function GoDown() {if(drawY < 461){ClearAndDraw();
            drawY = drawY + VelocityOfJetVarTWO;}/*down*/},VelocityOfJet);
        }
        },false);

document.addEventListener('keyup',function Up(e) {
    e.preventDefault();
    if(e.keyCode == 37)
        //left
        {clearInterval(goLeftVar);}//left
    if(e.keyCode == 38)
        //up
        {clearInterval(goUpVar);}//up
    if(e.keyCode == 39)
        //right
        {clearInterval(goRightVar);}//right
    if(e.keyCode == 40)
        //down
        {clearInterval(goDownVar);}//down
}   ,false);