Chapter 5 Fuel System Overhaul

CHAPTER 5 FUEL SYSTEM OVERHAUL As described in the Construction Mechanic 3 & 2 it is the job of the fuel system to send the correct quantity of fuel or fuel-air mixture to the engine at all times. To do this, the fuel system components must be clean and correctly adjusted or they will not function properly. After troubleshooting, when the problem has been identified and isolated, it will be your job to see that components of the fuel system are overhauled correctly. CARBURETOR OVERHAUL The carburetor has been designed and manufactured in literally thousands of makes and models. Therefore, it is not practical to discuss even a few of them in this training manual (TRAMAN). The basic principles of all carburetors are the same and may be found in the Construction Mechanic 3 & 2, NAVEDTRA 10644-G1, or U.S. Army publication Principles of Automotive Vehicles, TM-9-8000. The purpose of this section of this chapter is not to make you an expert in carburetor overhaul, but, to familiarize you with carburetor overhaul procedures in general. CLEANING AND IDENTIFICATION Before starting any carburetor rebuild, first you should know and make absolutely sure the carburetor is the problem. Good troubleshooting can save you a lot of time and work. Why overhaul when you could have done the job with a simple adjustment. Second, find out the make and model of the carburetor you are about to rebuild and make sure the rebuild kit for the unit that you are going to overhaul is on hand. There is nothing more frustrating for a person than to disassemble an automotive part like a carburetor only to find out that the rebuild kit is unavailable. Third, locate the technical manual and have it on hand for the job. Only now will you be ready to start by removing the carburetor from the engine. The first thing you should do after removing the carburetor from the vehicle is the initial cleaning, which will remove deposits of dirt and grime and allow the identification tags or numbers to be read. These ID numbers are stamped into the base of the largest part of the carburetor, or they may be found on a small metal tag screwed or riveted to the carburetor. (Remember, when you complete the overhaul job, reattach any identification tags to their proper place.) Before you dip the carburetor into the cleaning solution, remove items that may be affected by the cleaning solution. (These items could be electric solenoids, plastic parts, vacuum pulldowns, etc. They should be removed and set aside for individual cleaning and testing.) Dip the carburetor into the solvent and brush away any deposits of dirt or grease. Remove the unit from the cleaning solution, let it drip-dry, or blow-dry it using low pressure air. CAUTION Compressed air used for cleaning purposes should not exceed 30 psi. Wear goggles and other appropriate protective equipment when using compressed air. MANUFACTURER’S INSTRUCTIONS AND TOOLS As you know, modern carburetors are complicated assemblies. They cannot just be taken apart, cleaned out, and put back together again. Each overhaul kit has assembly instructions, an exploded view for parts identification purposes, and a specification sheet with it. If this paper work is not in the overhaul kit, find the manufacturer’s repair manual which is available in your technical library. Without this information and the proper tools, you may irreversibly damage the carburetor. If you adjust the carburetor improperly, poor engine performance may result. DISASSEMBLY AND CLEANING Carburetor disassembly and cleaning is basically a matter of logic and good judgment. Use common sense and work slowly. Some tips to follow are shown below. . Have the instructions handy. Read them first to find out any special disassembly techniques. . Make sure your work space is clean and well ventilated. . Use a small tray or container to put the reusable parts in that must be cleaned. This will help prevent the search for that lost or missing screw, 5-1