Re: johnson 5.5h model CD-20R
Has the engine sat for a while? If so, the carb could be gummed up and thus why it runs poorly... In a 2 stroke, there really are no fluids to check other than the lower unit oil... This should be changed every fall. My old '61 5.5hp took on a lot of water in the LU but I changed it every fall and it was always ok...
If it's not pumping water, don't run it... To change the water pump impeller, which cost less than $20, you have to remove the power head on that model but it's not as hard as it sounds... Only about 8 screws....
So 'worth the trouble' is subjective...for about $50 and a few hours labour you could potentially have a great running 'lil engine... Or compare the coat to a replacement...
Btw, it's always a good idea to check the compression on an engine before deciding to keep it or not... Just to be sure the insides are in good shape...