Abstract: A combined accelerator, for accumulating energy, and jar, for sudden release of accumulated energy, for delivering up or down jarring impacts to objects stuck downhole in a wellbore, includes upper and lower tubular members which are telescopically connected within an integral outer tubular housing. The upper tubular member is connected to a pipe or tubing string inserted into the wellbore and cooperates with the outer tubular housing through mechanical spring means so as to accumulate a selected amount of energy to be released as a jarring impact. The lower tubular member is connected to the stuck object and cooperates with the outer housing through spring biased, tapered latch bars, so as to provide a sudden energy releasing means. A threaded adjusting bushing is provided within the outer housing so as to allow selection of a desired amount of spring bias, imposed on the latch bars, thereby providing a convenient field means for controlling the amount of jarring impact imparted to the stuck object.