Arduino code problem

For some reason when I comment out the Serial print section in the main loop() the motors just keep running.

while (counter1<200){
  counter3 = counter3 + 1; // dummy action
  // Serial.print(counter1);
  // Serial.print(" ");
  // Serial.println(counter2);
}

With them in the while loop the motors turn the fixed number of times and then pause as expected.

while (counter1<200){
  counter3 = counter3 + 1; // dummy action
  Serial.print(counter1);
  Serial.print(" ");
  Serial.println(counter2);
}

One thing that has improved is the motors now seem to be turning at the nearly the same speed when given the same pulse rates and the robot base travels in nearly a straight line.

Forgotten how to insert code. The {:} pop up window didn't produce the desired result and I have forgotten where is was explained.

// Motor A pin assignments to L298N motor controller
const int enA = 11;
const int in1 = 10;
const int in2 = 9;
// Motor B pin assignments to L298N motor controller
const int enB = 5;
const int in3 = 6;
const int in4 = 7;

// motor A encoder counter
int counter1 = 0;
// motor B encoder counter
int counter2 = 0;

// button pins assignments
const int btn0 = 25;
const int btn1 = 24;
const int btn2 = 23;
const int btn3 = 22;

int counter3 = 0;

void forwardA(int rate){
digitalWrite(in1, HIGH);
digitalWrite(in2, LOW);
analogWrite(enA, rate);
}

void forwardB(int rate){
digitalWrite(in3, HIGH);
digitalWrite(in4, LOW);
analogWrite(enB, rate);
}

void reverseA(int rate){
digitalWrite(in1, LOW);
digitalWrite(in2, HIGH);
analogWrite(enA, rate);
}

void reverseB(int rate){
digitalWrite(in3, LOW);
digitalWrite(in4, HIGH);
analogWrite(enB, rate);
}

void turnOffMotorA(){
digitalWrite(in1, LOW);
digitalWrite(in2, LOW);
analogWrite(enA, 0);
}

void turnOffMotorB(){
digitalWrite(in3, LOW);
digitalWrite(in4, LOW);
analogWrite(enB,0);
}

// inputs to motors control
void allInputsOff()
{
analogWrite( enA, 0 );
analogWrite( enB, 0 );
digitalWrite( in1, LOW );
digitalWrite( in2, LOW );
digitalWrite( in3, LOW );
digitalWrite( in4, LOW );
}

void setup()
{

// Set all buttons as inputs
pinMode(btn0,INPUT);
pinMode(btn1,INPUT);
pinMode(btn2,INPUT);
pinMode(btn3,INPUT);

// Set all the motor control pins to outputs

pinMode(enA, OUTPUT);
pinMode(enB, OUTPUT);
pinMode(in1, OUTPUT);
pinMode(in2, OUTPUT);
pinMode(in3, OUTPUT);
pinMode(in4, OUTPUT);

pinMode(3,INPUT); // set as input
digitalWrite(3,HIGH); // enable internal pullup resister
attachInterrupt(digitalPinToInterrupt(3), encoder1, RISING); // interrupt initialization

pinMode(2,INPUT); // set as input
digitalWrite(2,HIGH); // enable internal pullup resister
attachInterrupt(digitalPinToInterrupt(2), encoder2, RISING); // interrupt initialization

counter1 = 0;
counter2 = 0;

Serial.begin( 9600 );
Serial.println("Starting up");

}

// interrrupt server routines for reading encoder

void encoder1()
{
counter1 = counter1 + 1;
}

void encoder2()
{
counter2 = counter2 + 1;
}

void loop()
{

// set encoder counters to zero
counter1 = 0;
counter2 = 0;
// start up motors
forwardA(200);
forwardB(200);

while (counter1<200){
counter3 = counter3 + 1; // dummy action
Serial.print(counter1);
Serial.print(" ");
Serial.println(counter2);
}

turnOffMotorA();
turnOffMotorB();

delay(3000);

}