i am trying to send data via Labview to my arduino board using serial communication.My problem is that the arduino reads only the first byte of sent data then when i change it ,it doesn't react.
For example when i start the communication i send '0' to arduino.I sees it.but while it is running i send '1' but it doesn't behave accordingly to it.
I noticed also that the board 'sees' sometime the new value after a random period of time.

void setup()
{
    Serial.begin(9600);
    pinMode(13, OUTPUT);
}

char data = 'F';

void loop()
{
    data = Serial.read();
    delay(50);

    if (data == '0')
    {
        digitalWrite(13, HIGH);
        delay(1000);
        digitalWrite(13, LOW);
        delay(1000);
    }
    if (data == '1')
    {
        digitalWrite(13, HIGH);
        delay(4000);
        digitalWrite(13, LOW);
        delay(4000);
    }

    data = '4';
}