The plugs show that you are definitely running rich, and it sounds like it is often running only on 2 cylinders. those 2 things together will add up to terrible gas mileage.
first thing to do is determine which cylinder is not firing consistantly. If you pull off a plug wire and run the sled. you should be able to tell. If it runs way worse, thats not the cylinder, If it doesn't seem to make much of a difference, thats the cylinder you need to work on.
Next, check to see if you are getting good spark to that cylinder. the problem could be as simple as a bad wire or spark plug cap. If you are getting good spark, then you need to look at the carb. check to make sure the Choke plunger is not sticking, and clean and adjust the carb if necessary. If you did not do it before the season, you should probably consider cleaning all the carbs. Also, you may need to look at rejetting. Sleds need different jets for different temperatures and altitudes. A jet that is right for 0 degrees will run way too rich at 35 degrees.
One last thing, with the way those plugs look, it's pretty possible you just have a fouled plug. So, before you do anything, you should try a fresh set.
Last edited by Wyelde; 12-16-2009 at 02:43 PM.