/// You can clean the outside with any carb cleaner but I have read data from Volvo that warned against putting high order solvents inside the injector. I cannot now find this information and I cannot absolutely say that it was not about older injectors. It was electric injectors though.

Since gas is the fuel used I immersed the injector in gas and allowed it to soak. Dirty gas is poured out and fresh introduced until the gas remains clear after soaking.