[Quzarx]

if (p1_sw_trig == 0)
{
pwm13 = pwm14 = Limit_Mix(2000 + p1_y + p1_x - 127);
pwm15 = pwm16 = Limit_Mix(2000 + p1_y - p1_x + 127);
}
else
{
pwm13 = (pwm13-127)*0.5+127;
pwm14 = (pwm14-127)*0.5+127;
pwm15 = (pwm15-127)*0.5+127;
pwm16 = (pwm16-127)*0.5+127;
}

The way this is set up, you are only getting data from the joysticks when the trigger is not on. You always want to get that data, so first, take
pwm13 = pwm14 = Limit_Mix(2000 + p1_y + p1_x - 127);
pwm15 = pwm16 = Limit_Mix(2000 + p1_y - p1_x + 127);
out of the if block, so that you get new data from the joysticks every loop.
Then, if the trigger is on, you want to divide by 2, not multiply by a decimal

pwm13 = pwm14 = Limit_Mix(2000 + p1_y + p1_x - 127);
pwm15 = pwm16 = Limit_Mix(2000 + p1_y - p1_x + 127);
if (p1_sw_trig == 1)
{
pwm13 = (pwm13-127)/2+127;
pwm14 = (pwm14-127)/2+127;
pwm15 = (pwm15-127)/2+127;
pwm16 = (pwm16-127)/2+127;
}

Because you are getting the data every loop, and the pwm values aren't set until the end of the loop, you can modify them all you want before that point. Previously, you when the trigger was enabled, you were taking the pwm value, which defaults to 127, subtracting 127, making it 0, multiplying that by .5, making it 0 again, and adding 127, making it neutral on the motors.

Another way to do this would be:

if (p1_sw_trig == 0)
{
pwm13 = pwm14 = Limit_Mix(2000 + p1_y + p1_x - 127);
pwm15 = pwm16 = Limit_Mix(2000 + p1_y - p1_x + 127);
}
else
{
pwm13 = pwm14 = (Limit_Mix(2000 + p1_y + p1_x - 127)-127)/2+127;
pwm15 = pwm 16 (Limit_Mix(2000 + p1_y - p1_x + 127)-127)/2+127;
}

In this case, you are getting the data from the joysticks in both if and else.