I agree that you should check for an air leak. You can get a meter with duty cycle function at sears for $30.
Running an engine too rich is a bad thing to do. Having a higher fuel bill is the least of your problems. The excessive fuel dilutes the oil and washes oil film off the cylinder wall. The engine will also foul plugs.
Running rich is a very unhealthy condition for your engine. Running lean causes excessive combustion chamber temperature and also causes problems. It needs to be taken care of.