Re: what plugs for 1990 johnson gt150
There are a couple of options but since we don't know anything about your set up we'll go with a conservative choice, the QL77JC4. That motor is kinda sensative about heat range so it's best to stay with Champion plugs, 87 octane, good oil and look for about 5800 as your target rpm with an average load. 6000 will not hurt the motor if you have a performance type hull.
