Re: '75 johnson carb rebuild
It starts with removing the air silencer cover and air silencer. Those two gaskets can be reused until they fall apart. The airbox cover gasket is not mission critical -- you can run without it until you get a replacement but you'll get a bit of oily residue on the floor of the engine compartment.
Remove carbs, disassemble, soak overnight in carb cleaner (metal parts only -- I use B-12), blow compressed air through all the passages (or aerosol carb cleaner), reassemble with new carb kits, reinstall, link & sync, go fishing. The kits have extra parts (they fit more than one model of carb).
Keep track of which parts were on which carb, and identify the top, middle & bottom carbs so you can get 'em back where they were. The rods linking the carbs just snap out of and back into their plastic grommets.
In 3 easy steps:
1. Don't panic, these carbs are remarkably simple devices.
2. Get a service manual. Highly recommend the factory shop manual (Seloc & Clymers cover too many models, the photo's don't always look like your motor).
3. Click on "Top Secret Files" at the top of this forum, follow the link to "Carb Cleaning & Rebuilding". Don't hesitate to post any questions here.
You can do it.