checking timing and got shocked?!

Another possible factor: If you don't have your other hand resting on the radiator support (or other metal), it helps reduce the chance of a shock.
 
You think that's fun? Try grabbing a live 220 wire by accident. That was life changing for me..lol. Yea, don't go grabbing a hold of all at the same time. Another possibility could be a cracked cap. The crack will be almost impossible to find, sometimes, but you'd get the same result when grabbing a cracked cap.
 
A guy at work (and member here) was putting up a shelf in his garage when he hit the main power supply to his house with a drill bit :rlaugh:

Shut down power in his neighborhood. Nobody understands how he survived but only his hand was fried.