Cant select checkbox dynamically

Hi,
I have an ajax call that returns a number of values.
With it I am assigning a value to an input text field (this works fine)
and trying to show a checkbox as 'checked'
I've tried a number of methods to try and check the checkbox dynamically but it simply isn't.
Is there something I'm missing?
using Jquery 1.9+
bootstrap 3

html segment

<div class="form-group form-group-xs">
<div class="col-md-4">
	<div class="checkbox">
	<label><input type="checkbox" value="1" class="styled" id="horsepower_check" name="specs[checks][horsepower]">Horsepower</label>
	</div>
</div>
<div class="col-md-8">
	<div class="col-md-12">
	<input type="text" class="form-control input-xs" value="" id="horsepower" name="specs[values][horsepower]">
	</div>
</div>
</div>

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Script segment

$('#horsepower').val(data['engine']['horsepower']['!value']);
$('#horsepower_check').prop("checked", true);

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