MG Car Repair: MGB Engine, spark plug wires, distributer cap

Question
I have asked a question on here before about my MGB. I have a 1974 MGB, and when we looked up the engine number, the site said it was 74 1/2 engine? But anyway, to the point of why I'm writing. Recently I came home from school driving the B and when I turned on my route and shifted down into second gear it died. It won't start again, so my brother and I push it to the side of the road. A neighbor helps pull it out of the road and tries to help me start it. Every time we tried to start it, it would make a clunking noise and struggle to idle and die. If I gave it some gas it would run above 1500 rpm, but otherwise it would die. We kept looking at the engine and saw that one of the spark-plug wires was unplugged. AHAH! WE THOUGHT IT WAS SO SIMPLE! When we plugged in the fourth wire, it just died and wouldn't run. It will run at high RPM on three cylinders. Thinking that that is not the best for my B, it is sitting. A buddy of mine works on old Packards, and other American cars seemed to think that is was a distributer cap problem. He also thinks it might be a timing problem. What do you think? I know someone who can tune it up, but I don't want to do anything with it until I have an opinion from someone who has some experience with MGs. I'm 16 and rather naive about the vehicle but trying real hard to learn. I live in Beebe Arkansas, and was wondering if you knew anyone around my area that worked on them or had any experience with the engines. Please help!
Jonathan in Beebe AR

Answer
Hi Jonathan,
Sorry, I don't know anyone in AR. Your symptoms do not in any way indicate what is wrong. There is however a standard procedure to diagnose a problem engine. I learned a long time ago not to try to imagine what is wrong but to just test and find out what is wrong.

All piston engines only require three items to run with conditions on each of the three. The three are, Compression, Fire and Fuel.
The conditions are,
Compression -- Enough compression, 125 to 180 PSI on a compression test.
Fire --- A good spark at about the correct time, A thick blue spark at the timing set down by the manufacturer.
Fuel --- A combustible fuel available to the combustion chamber, atomized by carburetors or an injection system and delivered to the combustion chambers in close to the correct fuel/air ratio.

First you must confirm that the engine itself is ok by running a compression test on all four cylinders. (a compression gauge is not expensive) The engine must turn over at least 4 or 5 revolutions and the throttle must be held open.

Spark can be roughly tested by removing a spark plug and reconnect the plug wire to it and lay the plug on a metal part of the engine and spin the starter and watch the plug. You should see a thick (thick as a pensile lead) and blue in color (not is bright sun light).
If it is orange or yellow and thin as a hair, it is not good enough. To do a rough test to see if the timing is so far off as to make an engine not run do this test, With the plug attached to it's wire and laying on a metal part of the engine, put your thumb over the plug hole and have someone spin the starter. When the piston comes up on the compression stroke it will push your thumb off of the plug hole with a "Pop" sound. The spark plug makes a "Click" sound. When the timing is close enough for the engine to start, it will seem as though the "Pop" sound has caused the "Click" of the spark. If it seems as though it is "Pop - Click" or "Click - Pop" then the timing is probably far enough off for the engine not to start. This preliminary quick test is sometimes used by mechanics to tell what is needed to be done.

To set the timing exactly, you either need a timing light or a static test light.

To do a preliminary quick test of fuel, most mechanics will just spray starter fluid into the intake while someone spins the starter to see if it will start. WD-40 will work in place of starter fluid. If it starts on the spray then they know fuel is the problem and thus know where to look for the problem.

There is no magic screw to turn to fix an engine that does not run, it requires testing to get down to a failed item.
Howard