Re: Old 18hp Johnson cutting out HELP!!!
Hi nathan. Sonds like you've guessed right. The black plug is give usually a give away that one of the cylinders isn't firing properly. When you say "older" Johnson, ho old is it exactly. I only ask because depending on the model you'll need different bits to fix it. If it's a pre-1974 model it should use the old mageto ignition system using points and condensers (i.e. a "tune up kit" = $20). If it's newer than '74 you'll probably have electronic ignition, which means you'll ave to track down a new "power pack". However, before you do any of that, check each plug to see if they're getting spark. The best way would be to get a $8 gap spark plug tester from an auto parts store. Remove the plugs from the motor and instert them into the tester one at a time. The spark should be able to jump a 1/4" gap. If it can't, then you probably need to repair/replace the ignition components. Either way it shouldn't be too expensive to fix. At worst you may need to buy a new coil, but with any luck you won't. Try test your spark, then let us know what you find. We can walk you through anything you might need to do. Great motor you got there and well worth trying to keep alive. Good luck.
