The problem most of the time when this occurs is that the valves need to be adjusted. Remove the valve cover and check the valve settings. There should be between .004" and .005" between the valve stem and the rocker arm when the valves are fully closed.
If this isn't the problem, then the next most likely cause is a broken compression release inside the engine. The compression release spring is located on the camshaft inside the engine. It is this spring that usually breaks. The entire camshaft must be replaced if the spring is broken.
If you don't feel comfortable with this kind of repair I would suggest sending it to a reputable shop.
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