If the screw is tight the gas is probably coming from the overflow tube in the carb bowl. The float might be sticking or there might be some dirt keeping the valve from seating. It's fairly easy to take apart the carb and give it a good cleaning. Does it leak all the time or leak for a while and then stop?
You can see the overflow tube here. <a href="http://www.hondaforeman.com/phpBB2/view" target="_blank">http://www.hondaforeman.com/phpBB2/view ... t=overflow</a>
You can see the overflow tube here. <a href="http://www.hondaforeman.com/phpBB2/view" target="_blank">http://www.hondaforeman.com/phpBB2/view ... t=overflow</a>