GAUGE GP-SIGHT 2233095 - Caterpillar

All 3500 Family Of EnginesFuel ratio control diaphragms (the lower 2W122 Diaphragm and the upper 2W121 Diaphragm) are serviced. See illustration. The 7C3998 Fuel Ratio Control Group is used on all 3500 Family of marine, industrial and generator set engines.
Location of parts.When replacing the diaphragms, be sure that a 7C4000 Screw Assembly is installed in the fuel ratio control group. This assembly has a steel screw and an aluminum piston that will improve diaphragm life, especially in high vibration applications. Also, be sure the 5H6005 Seal is installed on the 7C4000 Screw Assembly. This seal, together with the aluminum piston, reduces the sideways motion and fretting of the diaphragm. Always reset the arming pressure and level setting after replacing the diaphragms.
A special level setting may be required for satisfactory performance in some high altitude application