You can pry the little black limiter cap off the altitude adjuster to allow you to open the adjustment a little further. That will probably temporarily fix your issue. The jet that the altitude adjuster varies the size of is likely partially clogged. That (main jet) jet is right at the bottom of the float bowl and if any gas is left in the carb during storage, that is where the deposit builds up as it evaporates. Will cause low-power lean running that will stall the genny if a significant load is put on it. If that strategy gets it working OK again, plan on cleaning the carb jets once you are done using the RV. Onan discourages cleaning the carbs to sell new ones. Really are not too many "mechanics" capable of doing that anymore anyway. They are good, reliable carburetors that generally just have "dirty jet" issues. The main jet at the bottom of the float bowl is the most important and most often overlooked. Tricky to clean as the fuel supply enters it sideways from the altitude adjuster screw. A good overnight soak of the metal parts in lacquer thinner and "rodding out" of the passages with a broom straw (DO NOT use anything metal or you WILL be buying a new carb!!) will do the trick.
