MG Car Repair: 74 MG Midget wont start, starter solenoid, mg midget

Question
The car still won’t start. I have also been consulting with an old school mechanic that I know and he suggested checking the following, which I did with the corresponding results.

(I am jumping off of another vehicle’s battery)

With the key on, check the volts going to the positive side of the coil…    13.3 v
Then crank the engine and check the positive side of the coil…      10.5 v
If the volts drop significantly (more than ½ volt) hot wire across the
starter solenoid and try to start it…               11.0 v
I am not sure what these results show. I am supposed to get back with my friend tomorrow with the results. Just thought I would share them with you

Thanks,
Andrew  

Answer
Checking available voltage at the coil while cranking is a test to see if the load of starting is starving the coil of voltage thus causing a weak spark. The low threshold is 9v. If the coil is correct 10.5 to 11v should fire the coil ok. Even without a scope you can just put an extra spark plug on one of the plug wires and spin the engine (throttle open) and watch the spark. (not in the sun light) and you should see a thick blue spark. If it is a thin yellow or orange spark, you may have a problem. The spark at the plug wire is what the ignition system is trying to achieve so if you have it and the timing is correct, end of story as far as ignition is concerned. Providing the plugs are not fouled.
Howard