Try changing the oil to a good brand, I have seen a big difference in preformance depending on the oil I used in many of my past bikes. You may have worn fingers on the clutch basket or clutch hub. The clutch plates wear grooves in them and that makes it hard for the plates to slide on them when you pull the clutch. When the engine is running the force of the engine will force them to slide, but when it is not they want to "stick" making it hard to push while in gear. When they get real bad the engine will stall sometimes when you put it into gear. This a common problem on motorcycles. I have fixed them before they get too bad by pulling the basket and Lightly filing the fingers to take out as much of the grooves as poss. Don't get them too thin or they are prone to breaking. The grooves are caused most of the time by popping the clutch for example: to wheelie or burn out, and just age. Hope this helps.