Answer to "need repair advice on rv"If the accessory battery is not charging while hooked up to shore power, take a multimeter ad check the voltage coming out of the DC ports checking from + to - (or black to red) it should be around 14vDC. If its less, the converter needs replaced.
Answer to "it won't start. what can I do to start it?"pull the spark plug after trying to start it. It should either be dry or have gas on it. If its dry, the carb problably needs cleaned by soaking it in carb cleaner, and then blowing out every passage way with compressed air. If it wet with gas, try a new plug and see if it fires while holding it on the head, while pulling the starter rope. If it fires, replace the plug and try to restart it.
Answer to "Nipple on the bottom of the carburetor?"You may need to replace or clean the needle and seat, they are what shuts off the fuel flow when the carb is full of gas. Just a very small particle will cause it to not shut off.