BOLT-FLANGE HEAD 2818975 - Caterpillar

Excessive Fuel Fumes In Exhaust From Cranking
If an engine in this family is hard to start, excessive fuel fumes can accumulate in the exhaust system as a result of cranking the engine. This could occur because fuel continues to be injected and exhausted from the cylinders even though the engine is not firing. If cranking is continued with the fuel turned on and the engine starts, fuel fumes can be ignited from the hot exhaust gases. To prevent a buildup of fumes, take the following precautions:
... Wait a period of time before trying to restart the engine to allow the fuel fumes to dissipate.... Shut off the fuel and crank the engine for about 10 seconds so air can clear out the exhaust system. Then turn on the fuel and crank again. (See the applicable Service Manual for location of the fuel shutoff on vehicular applications.)Modifications To Prevent Fuel Siphoning Out Of Fuel Return Line (Industrial, Marine, Generator Set Engines)
Installations of these engines may require that the fuel tank be below the engine. After shutdown, fuel can siphon from the filters back to the tank. When the engine is started, it will run rough until the filters and lines are filled with fuel.
Either of the following two modifications can be made to the fuel return line to help prevent siphoning.
... Add a length to the fuel return line so part of the line is below the minimum fuel level in the tank. The level of fuel in the tank will act as a small pressure head and help prevent fuel from siphoning from the filters into the tank.... Add a vent tube at the highest point in the return line extending about 2.2 to 3.0 meters (7 to 10 ft) above the fuel filter housing. The vent acts as a siphon break and prevents the filters from draining.