QuestionI have a 1978 MGB with everything original except that the catalytic converter has been removed. The car hasn't run in almost 2 years. I checked the fuel to the carb and the spark and both of those are fine. When I try to start the car, it starts and then immediately dies. If I give it gas as I start it, it will start and run for a few seconds, idling around 1100 RPMs, but then the RPMs slowly drop until it stalls. Do you know what I can do to diagnose the problem? Please note that I have barely worked on cars before, so if I have to check something, I would greatly appreciate knowing how. I have a Hayne's manual, so if it's in there I can look it up.
AnswerHi David,
It only requires 3 items to run, Compression, Fire and Fuel. Compression usually will not come and go but fuel and fire will. Diagnosing by symptoms is a waste of time. The only way to arrive at a solution is to test. You said that "Fuel ad Fire are fine". That means that compression is coming and going. I don't believe it. The only way to test fuel and fire is at the exact time of failure. Fuel -- 1.5 PSI to 3 PSI AT THE TIME OF FAILURE. Fire --- A good spark at the plugs all the way down to the last RPM when it quits.
These are both easy to test and only require a few tools. Most vacuum gauges have a fuel pressure section. You need a "T" fitting and hose clamps. Also a timing light.
Put the "T" on the fuel line at the carburetor with a short piece of hose to the carb and the vacuum gauge or fuel pressure gauge on the other end of "T". This way you can SEE the pressure at the time it dies. It must maintain from 1.5 PSI to 3 PSI at all times. (this only tests fuel supply to the carb and not the carb itself. (Be sure to put clamps on all connections)
Connect the timing light up and tape the trigger down so the light flashes all the time. Then watch the flash of the light when it quits to see if the light went out first or the light flashed all the way to the last revolution as it dies.
A vacuum gauge and a timing light are not expensive and necessary tools to work on a car (or any engine) You don't need to purchase the professional mechanics tools, even Wall Mart has them.
If you run both tests and it still dies, get a spray can of starting fluid and spray a few shots into the intake at the time it is trying to die to see if you can keep it running on spray. If you can then you probably have a carburetor problem. If it still does not keep running then remove the "T" fitting and connect the vacuum gauge to a straight vacuum on the intake manifold and read vacuum as you try to keep it running. If you keep it at the 1100 RPM and the vacuum goes down toward zero before it dies then you have a stopped up muffler. To confirm this just open the pipe where you have removed the CAT and try it again.
One of these tests will net you a correction.
Howard
