Re: Spark problems on a Johnson 90 hp 1985 (Model: J90TLCOS)
What you're encountering is a common occurrence. The engine must turn over at least 300 rpms in order for the stator to energize the powerpack (ignition). The spark test is always made with the spark plugs removed so as to obtain the highest rpm which is needed to assure that the stator, powerpack, etc is functioning properly.
Now, with the spark plugs installed, obviously the rpms are drug down somewhat, and even when the engine is in tip top condition, if you took a spark test with the spark plugs installed, the spark would be rather erratic.... this one fires, that one fires, but not all fire in the normal sequence. This is normal in the starting setup.... one plug fires which increases the rpms immediately and the rest of the plugs fire accordingly.
However, if the engine has a poor battery, a tip top but undercharged battery, a loose cable somewhere, or a tight but dirty cable connection at some point... battery terminal, powerhead ground, solenoid, whatever.... this results in a voltage drop which in turn results in a low cranking rpm which will produce no spark/ignition.
So as "coueytwo" suggests, clean all cable and wire terminals and whatever component they attach to that pertain to the electric starter system. A slow cranking engine = no ignition.
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