Usually it's not trivial to find out that valves have to be replaced. Some common cases are: timing belt was broken and valves were bent, one or more valves where burn or have mechanical defect. The...
This must be a vacuum hose, with a connection to the intake manifold, at rear of carb.This must be an after-market distributor because the original "Lean Burn" computer did not have a vacuum advance...
When to Replace an Engine.
A bad internal knocking sound; excessive smoke out of the exhaust pipe when running; overheating; no power on exceleration; these are a few of the first indications.