Everybody's extruder is different. So it is hard to say. But a lot of times it is possible for the filament to get hung up after the hubbled bolt and not go into what ever pathway it is supposed to go. Or... Even once it has started into the nozzle, there is that teflon tube it can get hung up on. On thing that helps a lot is to cut a very sharp point from multiple sides on the end of the filament. That makes it less likely to get hung up. And it also helps to feed in a straight piece of filament instead of one with a tight curve in it. You might try taking a hair dryer and straightening the filament and putting a point on it. That might just do the trick.