MG Car Repair: 1979 midget stops running, bright sun light, compression stroke

Question
Hi Howard,

I have a 1979 midget 1500 with the single Stromberg carb.  After I have been driving for 30 minutes or so, the engine will just stop running and shut off, as if it runs out of fuel.  When this happens, after letting it sit for a few minutes, I can crank it back up and continue driving but I usually have to pump the gas several times while cranking before it will catch (Normally it fires up on the first turn of the starter.)  One person told me if the float has a pinhole, it can fill up with fuel and block the intake.  Any ideas?

Answer
Hi Dan,
Your symptoms do not tell you what is wrong so you need to do some testing and the tests must be done when the car is in the failed mode. (dead) Or better still, just when it dies. It is a waste of time to guess what is wrong as there may be a thousand possible causes. Testing is the only method to find the problem.

All engines only require 3 items to run, Compression, Fire and Fuel with conditions on each.

Compression --- It must be from 125 to 180 PSI with little difference between cylinders. Compression will not usually come and go so you can first look at the other two.

Fire ---- Fire (Spark) must be a strong spark and at about the correct time. You can do a preliminary test with only a plug wrench.

Remove #1 plug and put the plug on the plug wire and lay it on a metal part of the engine. Place your thumb over the plug hole and have someone spin the engine over. As the piston comes up on the compression stroke it will blow your thumb off of the plug hole with a "Pop" sound. At the same time the spark at the plug will make a "Click" sound. If the spark is ok, it will be a thick blue spark and it will seem as though the "Pop" is causing the "Click". If you have a "Pop"-"Click" or a "Click"-"Pop" then the timing may be out but timing will not usually go out and come back even though spark can go and come. (Do not run this test in the bright sun light)

Fuel ---- The fuel must be a combustible fuel available to the combustion chamber in about the correct air/fuel ratio and be at least atomized. On an engine that does not start, this is easy to test by just spraying a little starter fluid into the intake when trying to start. If the engine tries to start then fuel is your problem and you know to test further.

In a dealership we needed to know for sure which had failed and if your car had come to me with your symptoms, I would have attached a timing light to the plug wire and run the light out from under the hood and put the light under a wiper arm and tape a piece of cardboard over the light so I could better see the light from the drivers seat in the bright sun light. I then tape the trigger down on the timing light and put a "T" in the fuel line just before the carburetor and attach a long hose and a fuel pressure gauge and run that out from under the hood and place it under the other wiper arm so I could watch fuel pressure as I drove the car. (being sure to put clamps on all hose connections)

Now as I drive the car I can actually see fire and fuel pressure and can thus see which fails.  

As for the person who told you that a pin hole in a float can fill up and block the intake. Don't let them touch your car!

Howard