Johnson 150 Outboard Input?

[RogerA]

As stated check the compression. I have owned a 1998 model for 15 years and use it 50-70 times a year and it is still running just fine. Will be going fishing with it in a few minutes.

[Ranger690]

They can be great motors. If you like everything else, look into the motor. Do a compression test and inspect each spark plug. Look online to see what they should look like, if they are brand new, be suspicious. Hope all of them look the same. If some are clean/bronze colored and some are black carbon, be suspic ious. If some are dry and some are really wet, be suspicious. Have him start it cold. See how easy/hard it starts. Watch it idle and warm up. See that it idles down after a couple minutes. Should be idling at 900-1200 rpms on muffs in the driveway. It will be lower in the water with some back pressure. Once warm, rev it up a bit. Leave it at about 2000 rpm for a few seconds and see that it holds and doesn't miss or sneeze or cut off. Check forward and reverse. Cut it off. Pull airbox off and look into carbs. Sqeeze fuel bulb and watch for extra gas getting by inside or weeping/leaking around carb bowls. Don't worry if it is, it's easily fixable, just good to know.

Check lower unit lube. If it is super clean, be suspicious. He probably just changed it and you won't know if any water is getting in. Best case would be good, dark oil. Knowing it has been used, but now water. If it has water or milky, then you have seals that will need to be replaced


If you like all that, go to the water. Pay attention to what he does to get it running. See if he lets it warm up before going screaming down the lake. Run it at varing rpms. Get it good and hot, then shut it down and look over the rest of the boat while the motor cools a bit. Let it sit for at least 10 minutes. See how it acts when he starts it back up and see if it will hop back on plane. If it misses, sneezes, cuts off or struggles to get back on plane, then there is an issue to be worked on. This too can be fixed. Probably one of two things. A "link and sync" or repair/replace the VST (vapor separator res and/or pump. Run it some more and watch how it acts when he loads it on the trailer. This is a good time to see the same, issues. Loosing power under load. Can be fixed by the same methods.

If you like everything, you could have a "leak down test" down, which will tell you a bit more than a regular compression test. If cylinders/block is in good shape, most anything else can be fixed.