Move Your Feet: The Third Pull of the Snatch & Clean
Do you find that your feet never quite end up where they need to be when you snatch or clean? For example, they're always too far behind you? Try actively lifting your feet and replacing them flat on the platform, focusing on landing on the whole foot, not the balls of the feet, and directly under the bar. You might be surprised how much it improves your balance and position when receiving the lift.
Now before you go and tattle on me, I'm not necessarily telling you to lift your feet way up into the air. I'm saying make them separate from the platform enough that you can replace them flat and aggressively in the correct location. This doesn't require much air space, but it does require you be active and aggressive and precise. And having said that, a dramatic elevation of the feet during the third pull can in fact be a very effective lifting style that allows maximal downward speed by guaranteeing exactly zero resistance against that initial downward movement.
If you have trouble kicking your feet back and landing on the balls of the feet, try thinking of lifting your knees rather than lifting your feet, and of sitting your hips straight down with a vertical torso rather than pulling your hips back after you finish your extension.
Otherwise, you can have lockout trouble for numerous reasons, some of which have to do with inflexibility, although rarely the biceps. Usually it's the shoulder girdle and thoracic spine and even the ankles and hips causing the problem.
But it can also be an issue of poor structure/technique. This article may give you some ideas.
I have the same problem, never been able to straighten my arms all the way. this causes trouble for ANYTHING overhead. I have tried several things with little results. But the two things that have helped are; MobilityWod.com, this may take longer and a lot of work on your part, and Massage therapy, much better but cost more, and more relaxing