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1981 Johnson 15hp won't start, only backfires

dillon

Member
I can't seem to figure out the problem on this 1981 Johnson 15hp. I went through the carb so I know its getting gas. When I test for spark it has good spark. When I looked at a service manual it said to make sure the terminal wires were correct, no terminal junction on this motor. The timming seems to be off or at least it has the symptoms, I have gotten it to loudly backfire about 3 times now, timing? It has good compression and the flywheel is not slipping. What do you think? thank you in advance for any input.
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I'm not sure about yours, but I had a similar problem with 4.5 I finally realized the plug wires were switched. Must have happened the previous fall when I winterized the motor
 
I'll go with the swapped leads as well.

An easy check is to just swap the plug boots on the motor and try to fire it up again. If it runs well, then put the boots back on the other plugs and swap out the power pack to coil leads and your back in business.

Backfires are usually combustion happening in the exhaust cavity, so since the exhaust is closed when your piston is at top dead center, I will assume it is firing when you are at bottom dead center.
 
I reversed the plug wires to the coils and it fired right up and purred like a cat, don't know why I didn't try that before, I guess I just didn't think any one would have monkied with the wires, the wires looked like they hadn't been moved since it was new. thank guys
 
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