MG Car Repair: my 1975 MGB broke down .. help!, bright sun light, air fuel ratio

Question
so after a few days of glorious sunshine in sausalito, tonight we had this damp fog rip through.. I don't know if this is relevant but I started my 75 MGB and drove about 200 yds.. suddenly the car sort of died for a second and freewheeled.. like the engine cut out a little...
ok so i had been running low on gas.. needle was empty.. thought maybe i had jusr ran out... filled her up with my 5 gal spare in the trunk... started up again ... engine turns over fine but nothing... nothing firing...

is this bad/damp spark plugs ? or something more serious?

cheers
Aaron


Answer
Hi Aaron,
Your symptoms narrow the problem down to only one million possibles so you need to run a few tests to narrow it a little closer.

Most mechanics will tell you that the easiest car to fix is one that will not run. The reason is that all engines only need 3 things to run, with conditions on each.
1. compression --- It needs from 125 to 180 PSI on a compression test

2. Fire ---- spark must be strong and at about the correct time on each cylinder.

3. fuel ---- the fuel must be a combustible fuel and available to the combustion chamber and in about the correct air/fuel ratio

Compression will not usually just go away quickly without a lot of nasty metal crunching noises, so you can check that last.

Fire can be roughly tested with only a spark plug wrench. Remove #1 plug and place the plug on the plug wire and lay it on a metal part of the engine. Put your thumb over the plug hole and have someone spin the engine over. Each time the #1 piston comes up on compression it will blow your thumb off of the plug hole with a "Pop" sound. Each time it does that you will see the spark "Click" at the plug. The spark should be thick and colored blue. (thick as a pensile lead) (blue is good and yellow or orange is bad but it must not be in the bright sun light)
The "Pop" should seem to be causing the "Click". If the sounds are separate like "Pop"-"Click" or "Click"-"Pop" it may be too far out of time to start.

A fuel problem is easily tested by spraying starter fluid into the intake while spinning the engine over. If it tries to start then you do have a fuel problem.

Once you have narrowed the problem down to one of the three you can then test that system to narrow it further.
Howard