ok. i know the problem. could you try if this works for you
<!-- model specifications -->
<?php if( have_rows('model_specifications') ):
$firstrow = "1";
while( have_rows('model_specifications') ): the_row();
$ms_model = get_sub_field('model');
$ms_gpm = get_sub_field('gpm');
$ms_input = get_sub_field('input');
$ms_psi = get_sub_field('psi');
$ms_drive = get_sub_field('drive');
$ms_rpm = get_sub_field('rpm');
$ms_drive_rpm = get_sub_field('drive_rpm');
$ms_hp = get_sub_field('hp');
$ms_volt = get_sub_field('volt');
$ms_hp_volt = get_sub_field('hp_volt');
$ms_power = get_sub_field('power');
$ms_engine = get_sub_field('engine');
$ms_burner = get_sub_field('burner');
$ms_electric_start = get_sub_field('electric_start');
$ms_size = get_sub_field('size');
if($firstrow == "1") :
echo '<div id="model-specifications">';
echo '<table class="rwd-table">';
echo '<thead>';
echo '<tr>';
if ($ms_model) {echo '<th>Model</th>';}
if ($ms_gpm) {echo '<th>GPM</th>';}
if ($ms_input) {echo '<th>Input</th>';}
if ($ms_psi) {echo '<th>PSI</th>';}
if ($ms_drive) {echo '<th>Drive</th>';}
if ($ms_rpm) {echo '<th>RPM</th>';}
if ($ms_drive_rpm) {echo '<th>Drive RPM</th>';}
if ($ms_hp) {echo '<th>HP</th>';}
if ($ms_volt) {echo '<th>Volt</th>';}
if ($ms_hp_volt) {echo '<th>HP / Volt</th>';}
if ($ms_power) {echo '<th>Power</th>';}
if ($ms_engine) {echo '<th>Engine</th>';}
if ($ms_burner) {echo '<th>Burner</th>';}
if ($ms_electric_start) {echo '<th>Electric Start</th>';}
if ($ms_size) {echo '<th>Size</th>';}
echo '<th>Quote</th>';
echo '</tr>';
echo '</thead>';
echo '<tbody>';
endif;
$firstrow++;
echo '<tr>';
if ($ms_model) {echo '<td data-th="Model">'.$ms_model.'</td>';}
if ($ms_gpm) {echo '<td data-th="GPM">'.$ms_gpm.'</td>';}
if ($ms_input) {echo '<td data-th="Input">'.$ms_input.'</td>';}
if ($ms_psi) {echo '<td data-th="PSI">'.$ms_psi.'</td>';}
if ($ms_drive) {echo '<td data-th="Drive">'.$ms_drive.'</td>';}
if ($ms_rpm) {echo '<td data-th="RPM">'.$ms_rpm.'</td>';}
if ($ms_drive_rpm) {echo '<td data-th="Drive RPM">'.$ms_drive_rpm.'</td>';}
if ($ms_hp) {echo '<td data-th="HP">'.$ms_hp.'</td>';}
if ($ms_volt) {echo '<td data-th="Volt">'.$ms_volt.'</td>';}
if ($ms_hp_volt) {echo '<td data-th="HP / Volt">'.$ms_hp_volt.'</td>';}
if ($ms_power) {echo '<td data-th="Power">'.$ms_power.'</td>';}
if ($ms_engine) {echo '<td data-th="Engine">'.$ms_engine.'</td>';}
if ($ms_burner) {echo '<td data-th="Burner">'.$ms_burner.'</td>';}
if ($ms_electric_start) {echo '<td data-th="Electric Start">'.$ms_electric_start.'</td>';}
if ($ms_size) {echo '<td data-th="Size">'.$ms_size.'</td>';}
echo '<td data-th="Quote"><a href="/request-a-quote/?">Request a Quote</a></td>';
echo '</tr>';
endwhile;
echo '</tbody>';
echo '</table>';
echo '</div>';
?>
<?php endif; ?>
<!-- end model specifications -->
