Outer Limits 4x4 Board

Hi i've got a 3y in my 4runner, and recently it'd started running really crappy, had no power and wouldn't rev cleanly..
So tonight i pulled the carby off and pulled it too pieces thinking a blocked jet or something, but no nothing, put it back on and it ran the same..
Thought i'd check the timing just to eliminate things, turns out its about 10 degree's retarded!!
So i adjusted it accordingly and it runs better than ever now..
My question is what could have caused the timing to jump 20 odd degree's? Stretched timing chain? distributer worn/jumped a tooth?
Its just frustrating, because its not something i would have considered, as the timing was checked less than a month ago..
Cheers Mitch

thanks for the help everyone..

Hi, there could be a number of reasons for timing to be retared, if its a points style distributor look for worn points, ie rubbing block, if there is no lubrcant can wear very quickly, check point gap & or dwell angle, check rotor for correct locating on shaft, check if mecanical & vac advance is working, thats an easy check with timing light, if you have an electronic distributor check all of the above eccept point gap, could also have problem with electronic module which could change timing at random, would be very unusal for a timing chain to be worn enougth to change timing that much without it making horrible noises, a jumped tooth on dist not likly as well but a worn or bent drive locating pin could be a possibilty, hope this is of some help.