Eventually fouling the s/plug in the lower cylinder indicates that either the bottom carburetor is flooding, the spark plug went bad... OR... (and most likely), you've lost ignition/spark on the bottom cylinder.
First: With "all" spark plugs removed, do a compression check. What are the individual psi readings of the numbered cylinders? The top cylinder is #1, bottom cylinder of course is #2
Do a spark test... The spark must jump a 7/16" gap with a strong blue lightning like flame... a real SNAP! Does it?
NOTE that a air gap spark tester can be purchased in most auto part stores.
********************
(Spark Tester - Home Made)
(J. Reeves)
You can use a medium size philips screwdriver (#2 I believe) inserted into the spark plug boot spring connector, then hold the screwdriver shank approximately 7/16" away from the block to check the spark or build the following:
A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.
Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:
..........X1..........X2
.................X..(grd)
..........X3..........X4
This can obviously be modified to a 6 or 8 cylinder setup tester.
********************
Also... Should that plug fouling substance turn out to be "water"... Obviously you'll need to remove the cylinder head in order to investigate that.
