A friend with an O-360 and -4.5 Ellison TBI has an issue where it runs significantly richer at full throttle after it warms up, enough so that it runs rough and throttle must be reduced to smooth it out. This has happened several times while doing touch and goes. Reducing throttle covers up some of the fuel delivery ports and the engine runs normally. My theory is that the sump is heating up the TBI as the oil comes up to temperature. I'm not sure I understand the physics of that, but there is a real correlation. Perhaps the warmth is helping with fuel vaporization and a more uniform mixture. The TBI is mounted to the sump with a gasket only. Will putting a phenolic spacer in there help by insulating it from the heat of the oil? Would the help with vaporization be missed at other than full throttle?
Ed Holyoke
Ed Holyoke