problem with hc-05 bluetooth

Hello, my project consists of a arduino UNO, motor shield and the HC-05 bluetooth module. My issue is that when I send the HC-05 commands such as right and backward, the wheel rotates perfectly. But forward, left is not working. I have connect 3 motors to adafruit motor driver l293d.

//1st motor
#define motor1a 2                
#define motor1b 4                
#define pwm1    3                
//2nd motor
#define motor2a 7                
#define motor2b 6                
#define pwm2    5
#define motor3a 8                
#define motor3b 10               
#define pwm3    9
// 3rd motor
#define motor4a 12               
#define motor4b 13              
#define pwm4    11              

char readString;

void setup() {
  Serial.begin(9600);
  pinMode(motor1a, OUTPUT);
  pinMode(motor1b, OUTPUT);
  pinMode(pwm1,    OUTPUT);
  pinMode(motor2a, OUTPUT);
  pinMode(motor2b, OUTPUT);
  pinMode(pwm2,    OUTPUT);
  pinMode(motor3a, OUTPUT);
  pinMode(motor3b, OUTPUT);
  pinMode(pwm3,    OUTPUT);
  pinMode(motor4a, OUTPUT);
  pinMode(motor4b, OUTPUT);
  pinMode(pwm4,    OUTPUT);
}

void loop() {
  while(Serial.available()) {
    delay(100);
   int data=Serial.read();

  if(data == '1'){
   Serial.println("Forward");
   forward(255);
   delay(50);
    }
    else if (data =='2'){
     Serial.println("Left");
    left(255);
    delay(50);
  }
  else if (data =='3'){
    Serial.println("Right");
    right(255);
    delay(50);
  }
  else if(data =='4'){
    Serial.println("Backward");
    backward(255);
    delay(50);
  }
  if(readString =='6'){
    Serial.println("Rightturn");
    rightturn(255);
    delay(50);
  }
  if(readString =='8'){
    Serial.println("Leftturn");
    leftturn(255);
    delay(50);
  }
  else if(data =='5'){
    Serial.println("Stop");
    Stop();
    delay(50);
  }
  

}
}
void forward(int pwm)
{
  digitalWrite(motor1a,LOW);
  digitalWrite(motor1b,HIGH);
  analogWrite(pwm1,pwm);

  digitalWrite(motor2a,HIGH);
  digitalWrite(motor2b,LOW);
  analogWrite(pwm2,pwm);

  digitalWrite(motor4a,LOW);
  digitalWrite(motor4b,LOW);
  analogWrite(pwm4,0);
}
void backward(int pwm)
{
 digitalWrite(motor1a,HIGH);
 digitalWrite(motor1b,LOW);
 analogWrite(pwm1,pwm);

 digitalWrite(motor2a,LOW);
 digitalWrite(motor2b,HIGH);
 analogWrite(pwm2,pwm);

 digitalWrite(motor4a,LOW);
 digitalWrite(motor4b,LOW);
 analogWrite(pwm4,0);
}
void right(int pwm)
{
 digitalWrite(motor1a,LOW);
 digitalWrite(motor1b,HIGH);
 analogWrite(pwm1,pwm/3.5);

 digitalWrite(motor2a,LOW);
 digitalWrite(motor2b,HIGH);
 analogWrite(pwm2,(pwm*6)/10);

 digitalWrite(motor4a,LOW);
 digitalWrite(motor4b,HIGH);
 analogWrite(pwm4,pwm);
}
void left(int pwm)
{
  digitalWrite(motor1a,HIGH);
  digitalWrite(motor1b,LOW);
  analogWrite(pwm1,(pwm*6)/10);

  digitalWrite(motor2a,HIGH);
  digitalWrite(motor2b,LOW);
  analogWrite(pwm2,pwm/3.5);

  digitalWrite(motor4a,HIGH);
  digitalWrite(motor4b,LOW);
  analogWrite(pwm4,pwm);
}
void leftturn(int pwm)
{
  digitalWrite(motor1a,HIGH);
  digitalWrite(motor1b,LOW);
  analogWrite(pwm1,pwm);

  digitalWrite(motor2a,HIGH);
  digitalWrite(motor2b,LOW);
  analogWrite(pwm2,pwm);

  digitalWrite(motor4a,LOW);
  digitalWrite(motor4b,HIGH);
  analogWrite(pwm4,pwm);
}
void rightturn(int pwm)
{
  digitalWrite(motor1a,LOW);
  digitalWrite(motor1b,HIGH);
  analogWrite(pwm1,pwm);

  digitalWrite(motor2a,LOW);
  digitalWrite(motor2b,HIGH);
  analogWrite(pwm2,pwm);

  digitalWrite(motor4a,HIGH);
  digitalWrite(motor4b,LOW);
  analogWrite(pwm4,pwm);
}
void Stop()
{
  digitalWrite(motor3a,LOW);
  digitalWrite(motor3b,LOW);
  analogWrite(pwm3,0);

  digitalWrite(motor4a,LOW);
  digitalWrite(motor4b,LOW);
  analogWrite(pwm4,0);

  digitalWrite(motor1a,LOW);
  digitalWrite(motor1b,LOW);
  digitalWrite(pwm1,0);

  digitalWrite(motor2a,LOW);
  digitalWrite(motor2b,LOW);
  analogWrite(pwm2,0);
}

I could see all the commands such as forward, left , right and backward in serial monitor but only right and backward commands are working.