When I have a full tank of gas, the car runs very smoothly and hardly smokes. When i get under a 1/4 of a tank it starts to smoke and runs and idles like crap. JW if anybody knew what the problem is because I have no clue.

 

I wouldn't be suprised if there was crap/water in your gas.

 

When you start to run your tank low on gas any sediment in the bottom of the tank is stirred up more and more as you get more low on fuel which in turn causes it to pump to your fuel filter and or carb-t/b, now if it did it all the time id have to say fuel filter but most likely not in this case. Best thing to do and doesnt take much time, is to drop your tank and have a look inside if there is anything other than gas in it then you need to have it cleaned and replace your fuel filter as well, and if it is fuel injected then you might get a little gunk on your injectors from build up. But this sounds of a contamination in your tank most likely.