85hp - 140hp powerhead swap?

Hello! I have a 1980 Johnson 85hp. A friend has a 1979, i believe, 140hp powerhead that has been in his airconditioned garage for about 20 years and ran great then but twisted a shaft in the lower unit. The lower unit is long gone, but the powerhead is there and complete. 2 questions:

1. Aren't lower units from '78 - '80 compatible with all 85-140hp powerheads?

2. What advice can you all give in regards to going through and getting a 30 year old motor in storage for the last 20 years up and fresh as new?

Thanks in advance.

-Josh in NC

Re: 85hp - 140hp powerhead swap?

You shouldn't have any problem making the powerhead switch. Here are some things you need to watch out for: You did not state that the 140 came with carbs. If you run the 140 with the 85 carbs, it will be underfueled and it could damage the powerhead. You really need the large 140 carbs. I'd completely disassemble the carbs and overhaul them. Take the jets out and pressure clean all passages with a good aerosol carb cleaner. The lower unit will need fresh oil. You will want to change the lower unit impeller. If you have original fuel pumps and fuel lines under the cowling, they were not compatible with today's ethanol fuels. They will deteriorate, so they should be replaced. The thermostats and pressure relief valves in the thermostat housing under the exhaust bubble are a bear to access when the powerhead is mounted on the midsection. Prior to mounting the powerhead, I'd replace the stats and check the pressure relief valves when they are easy to get to. Run a 3/8" fuel tank hose. Get a factory service manual and use to to do the sync and link as that will need to be reset with the new powerhead. You should see a significant performance difference with the new powerhead.

Re: 85hp - 140hp powerhead swap?

Thank you emdsapmgr! Outstanding info. The 140 is complete with carbs. I did plan to rebuild them and clean out the jets as well as a new fuel pump. I hadn't thought of the thermostats and pressure relief valves. Thanks again

-Josh in Havelock