Questionthe mg wants to go, it turns over like it should.starts then dies,getting fuel to the carbs. checked fuel pump 1.5psi.replaced it.vacume about a 5 probably should be about 14.really confused on what i should do next. hopping you can help Richard
AnswerHi Richard,
1.5 PSI on fuel was ok. I like to see from 1.5 to 3 PSI.
However, there is a order in testing an engine that don't start and you checked fuel first and that should always be the last thing tested. An engine must first be a good engine to start and run so Compression must be first of the only three systems that must be tested.
It is good to test vacuum but again that is secondary to Compression. Compression must be first as it tests the combustion chamber to see that this engine can run.
Remove all the plugs and remove the power wires from the coil (white wires). You need to see from 125 PSI to 170 PSI on all cylinders (throttle open). If you don't get that reading it is a waste of time looking at anything else.
(5 in hg on a cranking vacuum is low but are you sure the throttle was closed)
Second to test is fire (ignition) Even if you don't have a scope to test the ignition system there are ways to do a rough test. With the plugs still out and the white wires connected back on the coil, connect the plugs on to the plug wires and lay the plugs on a metal part of the engine and have someone spin the starter and watch the plug fire. (not in bright sun light) You should see a thick spark (as thick as a pencil lead) and blue in color. If it is thin as a hair and yellow or orange in color it may be too weak to start the engine.
Put a timing light on #1 plug wire and check ignition timing.
If all that tests correctly and only if it tests correctly should you proceed to Fuel.
Fuel system is easy to test. Just spray a little starting fluid into the intake when trying to start it. If it starts up (even just for a few seconds) you do have a Fuel problem. Especially if you can only keep it running by spraying starter fluid into the intake. If this is the case then is the time to test the Fuel system and the first test is what you already did in checking fuel supply (1.5 to 3 PSI) If that is ok you have a carburetor problem. (since you already found a vacuum problem you should look for possible vacuum leaks. The 73 "B" had two SU carburetors and a balance bar cast into the intake manifold so don't forget to look at the end plugs in that balance bar. Check the intake manifold for any up and down play by lifting and pushing down on the carbs. This checks for loose manifold nuts. This does not rule out a blown gasket but I have found them loose at times.
There are only three things to stop an engine from running and they are Compression, Fire and Fuel. (with conditions on each) but I found from working for many years in dealerships that you should test each system in order and not skip anything. Once you establish which system has failed then that requires new tests of that system. Let me know which system has failed and I will give you tests for that system.
Howard
