Although I don't have specific experience with these engines, I like
MAXUM's answer.
1) To paraphrase
MAXUM's response: "coils generally work—or they don't".
2) When
fuel is the problem...
A properly-running engine (using gas containing ethanol) has an exhaust odor that is "sickly-sweet".
The exhaust of "over-rich" engines (indicating fouled plugs, sticking float, bad wires) will smell strongly of raw gasoline.
One that is
starved for fuel smells like nothing else I can describe. (Burnt fresh-cut grass clippings with a wet cigar thrown in?
)
Also, fuel-starved engines will sputter, cough, and backfire.