Re: johnson 25hp
It's pretty easy to do both.
Just unbolt the LU and when it drops down an inch or two and stops look in the gap and there will be a bolt on the shift rod you will have to remove.
Install impeller per instructions.
When you go to install the lower unit you will probably have to turn the fly wheel in order to line up the splines on the drive shaft.
Carb is easy as well. If you have one of those CHEAP plastic carbs make sure you don't torque the plastic covers down tight when you go to re-assemble it. They will crack.
Sea Foam isn't going to do anything for your carb. Sea Foam has never done anything for my outboards but it might help yours. Won't hurt nothing.
If you get stuck on something do a search on how to fix it if you want instant answers.
