Document n9Ye1dvv3QJXZ9XwRxE8jKkda

CHAPTER 4/THE FUEL SYSTEM 32 changed every 10,000 miles or at tune-up time. More frequent replacement may be necessary if the vepicle is subjected to lots of dust or off-theroad travel. Heavy Duty Air Filters Heavy duty air filters come in a variety of shapes and si2es. They all have a minimum effi ciency rating of 99-9%. These filters are much larger than light duty types, so a tighter, more efficient paper can be used, while still letting enough air pass through with minimum res triction. based on a number of factors: miles traveled, hours of operation or restriction reading. The restriction reading, or pressure drop of these filters is almost always measured in inches of water. A U-tube monometer is hooked into the clean or engine side of the filter, the engine is oper ated at maximum speed, and the restriction is noted. A round dial type gauge can also be used to determine the restriction reading. This gauge may be permanently mounted in the dashboard of the vehicle. If these methods are not convenient, heavy duty air filters may be replaced on a routine time or mileage basis. Servicing Heavy Duty Air Filters 1. Heavy duty pleated paper--provides minimum of 99 9% efficiency for maximum engine protection. 2. Plated perforated oPexpanded metal inner and outer bodies--protect paper and strengthen filter assembly. 3- Adhesive plastisol--permanently bonds paper to metal end caps. 4. Plated metal end caps--will not warp or rust. 5. Low compression--set silicone gasket is perma nently bonded to the end cap. May be used over and over again, even after cleaning. THE FUEL FILTER A carburetor has many small passageways and intricate parts which can be damaged by dirt particles. A dirty carburetor can cause faulty performance and eventually complete engine shutdown, so the fuel must be as clean as possi ble to ensure smooth operation of the vehicle. There are a number of ways in which con taminants may enter the fuel system of a vehicle: 1. Unfiltered fuel may be pumped into the vehicle tank. 2. Tank caps may be loose or sealing gaskets may be faulty. 3. Rust--a powerful abrasive--may flake off from the fuel tank and fuel lines. 4. Contaminants or dirt particles may be left in the tanks or lines during the manufac turing and assembly process. Types of Gasoline Filter Systems (Figure 39) Features ofHeavy Duty Air Filters. Because of the wide variety of heavy duty air filters available, we will only cover the basic procedures of servicing them here. Their replacement time or service schedule may be (Figure 40) In-tank Fuel Filter.