There are tons of info on it out there if you search. I've also resurrected a lot of them so don't be afraid to ask.
If the problem is not obvious, conducting a pressure / vac test is invaluable, but start with the simple stuff.
For example, have you checked the carb setting? An 046 carb should not have limiters (unless it has been replaced). Check the Hi screw first (top left). Gently turn it all the way in (clockwise) keeping track of how far you turn it till it bottoms. If it is not close to a full turn out (or more) that could well be your problem.
Springs keep the old needle valves from moving. New springs DO NOT come in a rebuilding kit. I had to order them from a Stihl Dealer (they were only 50 cents each a decade or so ago). If vibrations are making your valves move, you need new springs. A full carb rebuild would also be a good idea. Old diaphragms get stiff and don't work right (your impulse line works as an air pump that makes the carburetor work). If the diaphragms are stiff, you don't get enough fuel.
Next, pull the muffler and see if your piston / cylinder is scored. If it is only scored on the exhaust side, that is a heat (or lean) problem. If it is scored on both the intake and exhaust sides, it was likely straight gassed. Running it with a bad cylinder (scoring) can make it go bad fast. Also, if you pull the recoil slowly you should be able to feel the compression. If it is lacking, don't overlook simple stuff like a loose sparkplug.