I would start by checking all the fuel lines, and the filter for leaks. Briggs had a problem with some fuel filters splitting a few years back, so check that also. Just mainly need to check for wet gas spots.
Depending on temp variations could be just tank venting through the cap, if stored in an enclosed area.
Thanks for the reply, I looked at the gas line, and fuel filter. It was all caked in oil and dirt so I cleaned it off with some degreaser.
I noticed that the "cap" at the bottom of the float bowl on the carb was loose. I dont know what this is for, it has a sensor wire attached to it. Anyone know if this will cause the smell?
I screwed it back in place, cleaned out the air filter and checked the oil, there was no gas in the oil, and it was nice and clean.
*EDIT* After checking out a couple of youtube videos, this "cap" is acually a solenoid used to stop the float chamber from filling up after the engine is shut off, it holds the bowl to the carb body, so it was probably letting gas leak down through the loose threads. I will give it a day for the carb cleaner to evaporate and stick it back in the garage to see if it still stinks..