So what is it doing without the filter and lid? still not run right after 2nd gear? Oh, do not ride this thing without a filter. Your pretty, new topend will go bye, bye. Do you have a fuel filter on the quad? If your fuel line is long enough, take the filter off and see if it helps. It sounds like it's leaning out. Take off the seat and filter and look at the carb slides through the filter opening. there should be a small gap under each slide if the slides are not in backwards. once your looking at the slides, slowly push the throttle lever and see if both carbs slide up at exactly the same time. I do not recomend riding the machine until you figure out what is making it do what it's doing. If you do and it is leaning out, kiss your top end good bye. possibly the crank too since the oil in the fuel lubricates all of the crank/rod bearings too. Let us know what's going on as of now.