I have two problem with the Spark Control System on my '79 Celica. First, I noticed that regardless of throttle position, the port on the carburetor that connects to the TVTV valve is clogged (no matter where the throttle plate is, i can’t blow air in or out). I suspect that it may have been clogged by a deteriorating vacuum hose.
The second problem is that a piece is broken off of the TVTV which is between the TVTV and the distributor diaphragm.
According to the manual, timing is changed only when the engine is cold. So, is this worth fixing? Mileage is 24 mpg (typical of 79 Celicas), and the car passed emmissions tests (although its no longer required in my state, I have it checked anyhow).
Short of pulling the carb, how does one clear the vacuum port?
Sometimes a brief squirt of aerosol carb cleaner followed by applying some high pressure air with a blow gun will do it.