My gas mileage lately has been all over the board, one minute I am getting 10-13 mpg then the next I am lucky if I am getting 2-3 mpg. It has a 400 in it. I have given it a complete tune-up even replaced the distributor. The carburator is about a yr old. I did have a problem with the automatic choke not working properly, but I got that fixed. I can literally say I have watched the gas gauge move almost as fast as the speedo. I am completely baffled by this.