I have an '03, 9.9 four stroke Johnson, model J10TBL4ST (made by Suzuki). It runs, but at half RPM and seems to be missing on the bottom clyinder. I get a very good spark across a 7/16" gap on both spark plug wires. If I bypass the the top spark plug to my gap-jump tool, the motor runs, but misses and usually dies when running on only the bottom cylinder. If I bypass the bottom spark plug to my gap-jump tool, the motor runs fairly smooth when running on only the top cylinder. I switched the top & bottom spark plugs to see if I had one bad spark plug and it runs no different.
Is it the coil (it has only one with two outputs) or possibly the cdi box? Can I test them on this model with a digital multimeter? This is a very low hour motor and has been stored inside, all connections look new. The spark plug thread is smaller than my compression guage adapters, therefore I have not tested it yet, other than with my thumb over the hole to feel pressure and vacuum present.
Is it the coil (it has only one with two outputs) or possibly the cdi box? Can I test them on this model with a digital multimeter? This is a very low hour motor and has been stored inside, all connections look new. The spark plug thread is smaller than my compression guage adapters, therefore I have not tested it yet, other than with my thumb over the hole to feel pressure and vacuum present.