MG Car Repair: 1977 MG Midget starting problems, zenith stromberg, carburetor rebuild kit

Question
Dear Howard,

I need your help please!  I bought a 1977 MG Midget that was sitting for 10 years.  The owner explained that the carburetor gave him issues that he could not fix.  My father and I are working on this project and he knows a lot about cars, as I am just starting to learn.  We have tried everything and still seem stumped!  After removing the fuel tank, I cleaned it and painted it and left it to dry.  I air pressured the fuel lines, and replaced the fuel line into another fuel tank which i put temporarily in the boot. I drained the oil from the engine, gearbox and diff, and replaced with new oil.  I turned the key and eventually we got it to start for literally two seconds before it died.  After MANY attempts it would not start again.  We checked the fuel intake and at first seemed to have some consistant flow issues but then seemed fine.  The spark plugs are sparking.  We removed the fuel intake to the carburetor, and used carb starter, which once again after MANY attempts finally started for a second and died.  We have checked and made sure of the correct firing order.  We have bought a carburetor rebuild kit, and also a diaphragm kit and a metering needle.  Replaced everything and the carburetor looks like there is nothing wrong.  It is a Zenith Stromberg 150 CD carburetor which from posts online seem to give issues (no answers online have helped solve my problem yet).  We even bought a manual for the carburetor and my Dad has checked everything and says there is nothing he can find wrong with the carburetor.  Is there anything we can try that you can think of please, because we are at that stage of thinking about buying a new carburetor which will mean more dollars to my budget which I'm not looking forward to.  

Any help would be greatly appreciated!!!

Kind regards,

Travis

Answer
Hi Travis,

Over the years working in dealerships I received many cars that had been stored for different lengths of time and often hear the same as I heard you say.

Any time you have an engine that will not start you need to try to clear your mind of any possible cause and go through a series of tests that will always have you arrive at the correction and a running engine.

There are only three items that make a gasoline engine run. They are Compression, Fire and Fuel.

The "Compression" must be sufficient on all cylinders (which also produces a intake manifold vacuum)

The "Fire" (ignition) must be strong (blue spark) and thick as a pencil lead and be about at the correct time (in degrees of crankshaft movement).

The "Fuel" must get into the combustion chambers in roughly the correct fuel/air ratio and be a easily vaporized condition.

The tests MUST be in that order and nothing skipped or guessed at.

Most people don't have a scope nor an exhaust analyzer but you can still run the tests with only a few inexpensive tools.

FIRST test the compression (throttle OPEN) You MUST see from 125PSI to 170PSI on each cylinder with very little difference between cylinders. If it has this run a intake manifold vacuum test. It should show from 15in to 28in and it MUST maintain that for at least 10 to 15 seconds of starter spinning and not decrease. (Be sure to have the throttle CLOSED during the test.)

There is a quick preliminary test that many mechanics use here. Remove #1 spark plug and put the plug wire on the plug and lay the plug on the head or any metal part of the engine. Put your thumb over #1 plug hole and have someone spin the starter. As the #1 piston comes up on compression it will blow your thumb off of the hole with a "Pop" noise. If you watch the spark plug you will see it spark with a "Click". If it seems as though the "Pop" is causing the "Click" the timing is close to correct enough to start. If however, you get a "Pop-Click" or a "Click-Pop" the timing is far enough off that it may not start. (The spark color should be blue (not in bright sun light) If it is orange or yellow and thin like a hair the spark is weak and may not start.

If the first TWO are correct you can proceed to "Fuel" but only if the first two are correct.
This is an easy test. Just have someone spin the starter while you spray starting fluid into that air filter. If it starts but wants to die just keep spraying starter fluid to keep it running. If you can keep it running on starting fluid you have a Fuel problem and that requires additional tests.

Let me know and I will tell you the next tests. DON'T SKIP A SINGLE ITEM!

Howard