GEAR AS-IDLER 4337057 - Caterpillar

3208, 3304, 3306 Engines Equipped With Sleeve Metering Fuel SystemsThe use of plastic tubing and brass couplings as a fuel supply line on the above engines can cause air leakage into the fuel system. Air in the fuel system will cause difficult starts, rough operation, low power and too much white smoke on start-up.
In applications (usually Original Equipment Manufacturer's product) where plastic tubing and brass couplings are used for fuel supply lines, it has been found that the plastic tubing can hold the vacuum in the line as the temperature increases. But, as the temperature decreases, pressure decreases, and the tubing and couplings become loose. Air then leaks between the couplings and tubing and enters the fuel system.
To correct this problem, use steel tubing or reinforced flexible hose and high pressure fittings instead of plastic tubing in the fuel supply line.