Thermal stressing of aviation fuels can promote the formation of fuel insoluble compounds. Their presence within the fuel system is troublesome to aviation gas turbine manufacturers as they can adversely affect engine performance. To study this phenomenon an experimental program based on a fuel rig capable of reproducing relevant engine conditions and featuring an instrumented replica fuel injector feed arm was devised. The initial objectives are to rate quantitatively the effects of bulk fuel and metal temperatures, fuel flow rates and fuel types on the production of fuel insoluble matter, both deposited and suspended. This report presents the initial results which indicate a relationship between the weight of “tube” carbon deposits and a function of “tube” metal temperature and fuel velocity. Further, this approach could provide the much interface between the engine and laboratory test results.