A while ago, someone on JBL posted a how-to guide for fixing the Viper Pit Vipers relative lack of mobility and ability to move their heads. Here is that link as a background reference, as it's nice to have all this info in one thread.
http://www.joebattlelines.com/forum...er=asc&start=15
Now here is my Yorktownjoe Solution.
First, choose the right tool for the job. I recommend a Black & Decker Wizard, but any rotory tool should work.
The next step is to sand down the tab inside the collar on the figure's back. This is the equivalent of chiropractic care for your Viper. Soon he will have full range of neck articulation!
Here is a picture of before and after side by side. You basically want to flatten that neck tab smooth.
The next thing you will want to do is CAREFULLY file down the crotch on the waist piece. If you have shaky hands, I would suggest the JBL filing solution. It will take longer, but you won't risk permanent figure dismemberment.
You may need to start slowly, then return to finish the job after you have confidence that the process is increasing the figure's poseability and leg motion.
Lastly, I suggest going with a bigger O-ring. This is an optional step, but it really helped my Vipers a lot. The top O-ring is stock with the figure. The bottom one is my larger O-ring suggestion.
Reassemble your Viper and he is ready for action! Let me know what you think of my solution. It worked for me, and I hope you will find it helpful.
Yorktownjoe