From your description of what is happening now that the governor is working, it sounds as if your choke may not be opening completely, or the air filter may be fouled up and restricting air supply to the engine. You should check that the choke is opening fully by inspection (remove the air filter and look at what happens when you move the control - the choke should open wide, so you are looking at the butterfly edge-on). While the air filter is off, inspect it and give its foam element a wash in clean petrol, then wet it with engine oil and wring it out.
The easy way to check for carburetor problems is simply to temporarily switch the questionable one for a known good one, and see what effect that has. If the problem moves with the carburetor, then the original carburetor is the source of the fault. Then you fix it, by following a manual.
I agree with Joe, that nickel plated spring doesn't look anything like the Lauson governor springs I have seen. If you made a major improvement by switching it for a standard Lauson spring, that is a step forward.
Now that you have parts that work, you should be able to sort things out quite easily.
