Hi Colin I just rebuilt the Zenith carb my late-model A-4, and the engine is running better than ever. Hope this perspective will help you:
First and foremost, if you have not already done so, get a copy of the A-4 Service and Overhaul Manual from Moyer Marine, which provides step-by step, illustrated directions. It will pay for itself not only for this job, but for work you may be doing in the future;
Have a space where you can keep your work organized. You’ll be removing and cleaning a lot of small parts, and it’s easy to mix things up, especially if you are interrupted or called away while you’re working. I used the lid from a small cardboard box, lined with paper towel, to keep the pieces in order as I dis-assembled, and to absorb any excess carb cleaner;
Take the time to ensure you are using tools that fit correctly. The jets you’ll be removing are made of brass, and easily damaged. Removing the main discharge nozzle requires an 11/32” nut driver-don’t even think about trying to use any other tool. Also, the idle jet is so small and prone to damage I don’t even attempt to remove it. Just spend a little extra time to ensure it’s clean;
The plastic tube that comes with the carb cleaner is great for getting cleaner into all the passages. Compressed air, with a small hand nozzle, is the best for blowing the stuff out, and ensuring the parts are clear. If you don’t have access to a compressor, or are working on-board, the canned air sold in office supply stores, for cleaning computer keyboards, will get the job done. Ensure all parts are clean and dry before re-assembly;
Double-check the float valve seat, using a magnifying glass, to ensure the needle will seat correctly. The Moyer manual shows how to dress the seat, using a 3/16” hardwood dowel, if needed. Follow directions to re-assemble, then re-install the carb on the engine. This is a good time to inspect and ensure all fuel-system components are installed and fastened correctly, before you start the engine.
This is one job you’ll enjoy. Let us know how it turns out !!