Agreed, if the batt cables are old and corroded (get rid of wing nuts at the battery terminals) and the engine ground is also rusty, you will have a low voltage to the ignition system issue when you hit the trim button because it draws a lot of amps. I had this years ago on my Cobra before I replaced all the OE battery cables and added a dual battery system. You may still need a carb rebuild though, the low voltage issue usually just causes an engine miss not complete stalling. Poor running at low speeds suggests plugged or dirty idle system in the carb.
