An old friend of mine would say, "Check the fuel  system."  He was almost always right.  Old dried up stuff in your tank from its days of rest may be your cause.  And it sounds like a partial blockage to me too.  So, yes, check out your tank from clunk  to the carb.  Could be in the carb now, if it was a piece of dried up crud floating around from  the tank.  So  clean her out begoinning to end.</p>

Cheers,</p>

Chip</p>