Properly tuned lift trucks deliver high performance, low CO emissions Key Concepts Fuel system, regular tuning, and air replacement are critical ingredients in indoor LP-gas performance and safety. Tuning the engine requires a balancing act between maximizing performance and minimizing carbon monoxide emissions. A detailed, step-by-step approach to tuning creates an efficient engine that has no problem operating under current OSHA indoor air requirements. Using engine-powered lift trucks for indoor operations is a long-accepted practice in industry. These lift trucks offer users an efficient, cost-effective, highly productive means for handling unit loads -- if the vehicles are equipped with the correct fuel systems, are properly tuned, and have adequate ventilation air replacement within the plant. These three requirements are vitally important to plant engineers involved in managing lift truck fleets. Basic tuning facts Between 70% and 80% of the engine-powered counterbalanced trucks in the U.S. burn LP gas. Because of its market dominance, this article focuses on the tuning requirements for LP-gas engines. However, many of the guidelines apply equally well to gasoline-powered vehicles. Lift trucks that use LP gas are equipped for that purpose by the manufacturer or are converted to burn the fuel by the dealer or end user. Unfortunately, the process of converting the engine from one fuel (gasoline) to another (LP gas) can lead to problems. All LP-gas powered lift truck engines use air valve carburetors; however, there are several versions available. Each engine has specific requirements for air intake (measured in cfm), and every LP-gas carburetor is designed to supply air at a predetermined rate. Installing an improperly sized carburetor on a lift truck's engine during conversion may create a fuel system that is impossible to tune correctly. For example, if the flow rate of the carburetor is too great, the engine does not have the airflow capacity needed to lift the carburetor's diaphragm/fuel and air valve assembly sufficiently to use the full stroke of the valves. The valve assembly only operates near the upper part of the fuel valve, and the result is an engine very difficult to tune through all ranges of speeds and loads. The first step in proper tuning is to make sure that the engine has the correct carburetor, and that it has been properly sized. The lift truck dealer is a good resource for this information. Balance performance / emissions The process of properly tuning a lift truck's engine involves a balancing act -- one that always involves compromises. For example, an LP-gas engine can be tuned to emit almost no carbon monoxide (CO), but its performance will be unacceptable. On the other hand, tuning for absolutely maximum performance may produce high levels of emissions as well as an unacceptable level of wear and tear on the engine. The object is to find the right balance between performance and emissions. Unfortunately, the reality is that many industrial users don't place enough focus on the importance of proper engine tuning. In fact, according to the National Propane Gas Association, improperly tuned lift truck engines outnumber those correctly adjusted. Although both gasoline and propane-powered engines are often poorly tuned, the problem is especially common for the LP-gas vehicles. In addition, other factors such as diaphragm failures or calibration shifts can result in high levels of CO emissions from LP-gas engines. Take a systematic approach Proper tuning of the lift truck fleet requires several steps. The engine and transmission should be at their normal operating temperature before tuning begins. Start by turning the idle fuel mixture adjustment screw all the way in, then backing it out 11/2 turns. The idle fuel mixture adjustment must be made when the engine is running at its normal idle speed -- typically 650 to 750 rpm. Confirm that the intake and exhaust valves are properly adjusted according to the engine manufacturer's specifications. The high-speed/full-power mixtures are controlled by the rotating valve at the carburetor fuel inlet. Typically, the letters "R" and "L" are marked on the body of the carburetor to indicate the rich and lean valve settings. This valve must be adjusted when the engine is at its full working load. When these adjustments have been completed, tailpipe CO readings should be 0.5% at idle and 0.2% at high speed/full power. Ignition timing should be adjusted to match the engine manufacturer's specifications. Remember that LP gas burns at a different rate than gasoline. If the timing isn't adjusted to compensate for this difference, the resulting retarded ignition time reduces engine horsepower and increases emissions. Depending on the engine manufacturer, recommendations on advancing the timing range from 2 to 14 degrees. Any higher advance other than recommended could produce unnecessary wear and tear on the engine. Speed of the engine governor should also be checked and adjusted to conform to the manufacturer's specifications. The air filter or cleaner should be checked. Any excessive restriction of airflow to the engine produces a pressure drop, decreasing the engine air supply while increasing the fuel supply. The result is reduced performance and increased emissions. Check the condition of the engine's spark plugs, points (if the truck doesn't have electronic ignition), and related components. Finally, check the operation of any other fuel system components, such as closed-loop fuel systems (including the oxygen sensor, CO control processor, and vacuum control solenoid). These systems usually include a warning light to signal any problems. After each vehicle in the fleet is properly tuned, work to keep them that way. The only viable solution is a regular planned maintenance program, performed either by the in-house staff or a dealer, and backed by the full support of management. An LP-gas powered lift truck with the correct fuel system, properly tuned, and operated within a facility with adequate replacement ventilation has no problem operating under current OSHA requirements. Looking for CO The level of CO emissions has a vital impact on the amount of air replacement needed to create a safe indoor environment. However, there are a host of factors, ranging from heating/cooling costs and air filtering needs, to more esoteric concerns such as ambient humidity requirements, that impact the calculation. Remember that engine-powered lift trucks are not the only source of CO in industrial settings. Thoroughly inspect the plant for other generating sources before concluding that the lift truck is the only factor in the equation. (Generally speaking, a propane lift truck requires about 5000 cfm of makeup air.) Other possible CO sources include: Exhaust from over-the-road trucks and tractor-trailers that enter the plant through the dock area Open burners and other types of oxygen-consuming process equipment Improperly vented heating systems and water heaters Other mobile equipment such as floor sweepers and scrubbers, and activities such as welding. All these factors, plus makeup air needs not related to CO considerations, should be incorporated into standard air replacement calculations. Tuning tools Before beginning, ensure that the engine is in good condition and the right diagnostic equipment is on hand. At a minimum, the tuning equipment tool kit should include: Compression gauge Feeler gauge tachometer Volt meter Vacuum gauge Timing light Carbon monoxide analyzer (two-gas or four-gas analyzer improves diagnostic capability). FORKLIFT OPERATION AND SERVICE. BE SURE TO VISIT THE HOME PAGE FOR INFORMATION ON LIFT TRUCKS REPAIR, SERVICE, TROUBLESHOOTING, AND EVERYTHING YOU NEED TO KNOW ABOUT FORKLIFTS AND THEIR USE.