ORIGINAL: dyerk

I have a J600 and am using a butane/propane mixture. Immediately after the engine has ignited the starting gas the EGT temperature climbs to 800C and shuts down. The egt probe is inserted by about 2mm and I have confirmed the EGT temperature is correct with another thermocouple. I dismantled the engine thinking there must be something wrong with the combustion chamber however everything looks fine. The engine is outside the airframe so there is no restriction for air entering the engine. When diagnosing EGT problems aside from the installation of the EGT probe what are some of the common things to look for.