MG Car Repair: 72 midget, wet test, running on three

Question
Hello Howard, my 72 midget 1275 was in storage for 16 yrs and after draining fuel tank and a major tune up it did fire but was running very rough. Almost like it was running on three cylinders. Rear carb was belching fuel mist now and then. Rebuilt carbs. Did compression check and front to rear was 135-130-130-125. Removed head and had a valve job done. Lots of carbon on valves. Pistons and cylinder walls looked good. Put back together and still is running rough. rear spark plug next to firewall is black and other three are normal. It does have blue smoke out the exhaust. Any suggestions would be greatly appreciated. Thanks Greg.

Answer
HI Greg,
Blue smoke is oil burning. If the rear plug is flat black it is too much fuel (unlikely because rear carburetor affects two cylinders not one). Shinny black is oil. About 4 squirts of engine oil in the plug hole and run another compression test. (throttles open) This is called a "Wet" test and will be higher than the dry compression test but it should not be more than 10% to 15% higher than the dry test. If the Wet test is a lot higher then you probably have a ring problem on that cylinder.

Any ignition problem on #4 can also foul that plug.