From these points, begin to adjust the idle adjustment screws until the idle is steady and smooth. Tuning linkage on sideways mounted tunnel ram carbs will take longer than a single 4 barrel. An alcohol carburetor is a different animal with very different requirements. Reduced Fuel Economy. The idle screw is adjusted on each carburetor until each one gives the same reading on the synchronization tool. If you are putting the car up for the winter, use this little trick. Whether you have a Demon or a stock HOLLEY carburetor, jetting should be fairly close if the carburetor is used in the intended application. However, adjusting the carburetor is a relatively simple job that can be done with a basic set of hand tools and a little bit of technical knowledge. The high voltage was delivered from the coil to the center of the distributor … A proper air/ fuel mixture is important because your engine uses the combustion it creates to burn the fuel appropriately, giving you good fuel economy and stopping issues like overheating. per hour which, as a consequence, necessitates the running of a belt-drive pump, but that's another story. For maximum horsepower, the coolest, most dense air possible should be available at the carburetor inlet. BlueOptimize software and is completely unique to Viezu. Spray the air bleeds with carburetor spray or WD-40 every week. ... At the lean end of the scale, the most important for fuel economy, most engines run into lean misfire at about 18:1 to 19:1 air/fuel ratio. BG Fuel Systems Stainless Steel Jet Extensions will correct this situation. When assembling a carburetor or reinstalling the fuel bowls, you need to adjust the float to be approximately 0.450" from the top of the bowl (in line with the bowl screw bosses when the bowl is upside down). This will assure that there will be no lean stumble when the carburetor comes off idle. Otherwise, air will flow across the top of the carb and out of the inlet tract rather than into the air horn. Also, whenever a carburetor spacer is added or removed, a camshaft, cylinder head or intake manifold change is made; it will be necessary to retune the carburetor to regain maximum performance. When the throttle is opened on a carburetor, the amount of fuel that flows into the main circuit is controlled by the carburetor’s jets. As long as the performance continues to improve, continue increasing or decreasing jet size. Fuel spilling out of the vent tubes is another possible cause. Many racers experience fuel delivery problems without ever being aware that something is wrong in their race car's fuel systems. Secondary adjustment is set with a screw accessible from the underside of the carburetor. This occurs when a car leaves so hard that G-force loading on the fuel in the secondary bowl causes it to be pushed up against the rear wall, uncovering the jets. It may just not perform to expectations. Maximum performance cannot be achieved unless the carburetor is wide open when the throttle is pushed to the floor. Therefore the equation for fuel flow is 1-H.P. Their race carbs come with billet baseplates and metering blocks, and as an added bonus, fuel feeds and sight glasses are found on both sides of the fuel bowls. All Rights Reserved. The basic rule of carburetor tuning is ignition first. Drag racing calls for a slightly different approach. If the fuel bowls are not full, the pressure is meaningless. Typically, a 600-HP engine will require 300-lbs of gasoline per hour and, by the same formula, an 800-HP engine needs 400-lbs per hour. With the engine running, slowly turn the mixture screws in or out as needed to establish the best idle quality. Proper care includes draining and flushing the entire fuel system, usually with gasoline. Open up the top of the tin-can and insert the two or four carburetor fuel lines from your regulator, switch on the system and carefully measure the time it takes to fill it. Recheck the float level with the engine running and the sight plugs out. The power valves function is to supply extra fuel for wide- open throttle, high load conditions. First off we need to rid ourselves of problem areas that can rob us of fuel economy. Keep in mind that valve springs, ignitions systems, torque converters, even engines have been changed, when all the time the fuel system was at fault. The actual results from any spacer or combination of spacers can only be measured during a test and tune session on the specific engine combination being run. There should be a minimum of three inches of clearance between the top of the venturis and a hood scoop. If you ran a single-cylinder engine, like the one in your lawnmower, under a load of 1-horsepower for 1-hour and weighed the fuel tank before and after, the tank would weigh approximately .5-lb (five-tenths of a pound) lighter. Under hood air is heated by the engine and headers and reduces the amount of power that can be produced. An alcohol carburetor is a different animal with very different requirements. This "dry" setting is to get you in the ball park. Highly-tuned racing engines can sometimes be more efficient, yielding B.S.F.C. Better combustion combined with the raising of the engine’s operating temperature from 160°F to 180°F were said to be responsible for vastly improved fuel economy. As the air density changes, adjustments to the fuel mixture are often necessary. A 700-HP tunnel-ram engine needs 350-lbs of fuel per hour which equates to a little over 85-lbs per float bowl. Spin the engine over with the ignition off and the throttle open and spray of WD-40 liberally down the venturi will leave a fine mist of protection on the valve seats and cylinders to prevent rust. For maximum performance, increase or decrease jet size two numbers (primary and secondary) as required. But the biggest payoff in fuel consumption is driving style. If a car leaves the starting line at 5000 RPM, the pump shot should begin at 4700-4800; an 1800 RPM launch calls for the accelerator pump shot starting at 1500. With mechanical fuel pumps, and some electrical pumps, a bypass is preferred rather than a regulator. Your engine may miss or "burn-up" parts. Performance will be poor if the accelerator pump nozzle (squirter) diameter is incorrect. Once you remove the filter and its housing, you will be able to access the exposed carburetor. Fuel levels that are two low may not cause the motor to miss or "burn" a piston, but they will reduce fuel flow and performance will suffer. Perform the gas-can test even if your car is running well - you have nothing to lose and everything to gain: including the prospects of improving your E.T. With the engine running at idle--usually 600 to 1000 rpm--the synchronization tool is placed over the inlet of each carburetor to get a reading on its gauge. If the car runs a little too hot, jetting up one or two sizes will alleviate the lean condition without hurting performance, because the ignition will burn off the extra fuel and cool the engine. For the hardest starting line launch with a foot brake, the pump lever override spring should be adjusted so that fuel starts to discharge through the nozzle at an engine speed lower than launch RPM. It may also shake when pressure is put on the engine. When setting idle speed, the butterfly openings should be adjusted equally both primary and secondary side. Traveling to tracks in different climates or at different altitudes may also cause a need for fuel mixture adjustments. You may notice that your car is slow to accelerate. Maximum airflow cannot be achieved if the throttle plates do not reach the wide-open position, or if it is pulled past wide open. Even though your car may not miss, pop, bang, skip or do anything else peculiar, it may not be getting all the fuel it needs to make maximum power. The carburetor also helps control the engine's speed when the gas pedal is pressed. Remember, fuel pressure is not a substitute for volume! Joos Mind/Getty Images. The most accurate method to tune a carburetor is with a wideband air/fuel ratio meter. Spacers and plenum dividers provide an easy way to change the configuration and the characteristics of the intake tract and the relationship it has with the carburetor. One regulator is sufficient in many applications. Can a fuel system that is too large hurt performance? Always jet for performance, not spark plug color. There is no substitute for a well-designed fuel and air delivery system. Viezu is the world's leading fuel economy tuning expert. Typically, the carburetor bowls are full at the starting line so the car leaves hard but in the process, drains the bowls dry. If a car is sluggish during initial acceleration and a puff of black smoke blows out of the headers when a drag car leaves the starting line, or when an oval track car comes off a corner, the accelerator pump nozzle diameter may be too large. Take your time and set the linkage up right! The process of producing horsepower revolves around the conversion of fuel into energy. With a drag car, plugs can remain bone white so attempting to read spark plugs is a waste of time. For consistent performance, a carburetor must be kept clean. So if we can see a good improvement in fuel economy with a leaner air/fuel ratio, then why don’t cars come out of the factory like this? For the same reason, only fuel filters specifically designed for racing, such as the BG5000 or BG Inline filter, should be installed. The use of two regulators is recommended in high horsepower engines to avoid excessive fuel restriction and provide adequate volume. The latter problem is easily cured by running a rubber hose from one vent tube to another, with a slot cut at the top of the hose. So what happens if fuel delivery is weak? Windshield snorkels are especially notorious for siphoning unless the rear is sealed. If a car is lazy or lays down at mid-track then pulls well in a higher gear, the engine may be experiencing intermittent fuel starvation. When you go up or down in jet size, it will either richen or lean out the fuel mixture for the entire fuel curve. Important Note: It's essential to observe two strict rules during the test. Their aim is for smooth running and maximising fuel economy. Using spacers between the carburetor and intake manifold can produce dramatic results. Log in, DAVID VIZARD’S HOW TO SUPER TUNE AND MODIFY HOLLEY CARBURETORS, The Tools and Equipment Guide for Engine Math Procedures and Measurements, How to Inspect & Clean a Holley Carburetor: Step-by-Step Guide, GM Muscle Car Handling and Performance Upgrades, How to Blueprint Engines: Rocker Arms Guide, Fine-Tuning Suspension for Maximum Traction, Perfecting the Combustion Process for More Power – Part 11, Blueprinting Engines: Valve, Springs, Retainers, Locks, How to Rebuild Ford Toploader 4-Speed Transmissions, Automotive Bodywork: Special Projects and Procedures, How to Improve Airflow in Holley Carburetors. The points switched electrical current to the coil which converted it to high voltage required to fire spark plugs. Any drag race carburetor with a secondary power valve must be turned sideways to avoid fuel starvation. On oval track cars, the same is true. For drag race cars, an Electric Fuel Pump is the best way to guard against fuel starvation. Clogged or dirty air bleeds can cause a stumble or a high- speed miss in an otherwise perfect carburetor. However, here is a starting guideline. Air bleeds become clogged from dirt and dyes in the fuel. Fuel economy is dependant on driving style, Taking an average 10% saving, this soon mounts up, if you a commercial driver doing long mileages then the remap will pay for itself very quickly. Another problem that will cause a stumble or hesitation is when the secondary jets become uncovered, and no amount of accelerator pump tuning will cure it. Most high-energy ignitions will leave very little residue on the plugs. For others (and most of our readers) the aim is to get the car running and performing better than originally intended. Jet size must then be increased accordingly. Higher pressure mechanical fuel pumps delivering alcohol, such as the 15-psi BG Six-valve, require a throttle bypass to supply the variable fuel pressure required by the carburetor. As with jetting, determining the best squirter diameter is accomplished by trial-and-error testing. Everyone knows the engine will make more power at night when the air cools. The engine should be at optimum operating temperatures. For many "a tuned car" is simply one running at peak efficiency and they would achieve this by a full service and adjustment to factory specifications. The typical improvement in bhp (brake horse power) of an Angel Tuning remap is up to 50% for turbocharged vehicles and 15% for naturally aspirated vehicles. At some point, ET or lap times will start to fall off, which means the mixture has been moved past the optimum air/fuel ratio. Exactly this combination of present torque at a certain RPM is the secret to better fuel economy with RaceChip. Use of a fuel filter is strongly advised as long as it doesn't restrict fuel flow. The denser the air, the more you can get into the cylinders. Whenever jet extensions are installed in a carburetor equipped with a secondary power valve, the power valve must be removed and the hole plugged. High 10-second cars will need to pump 1-gallon in 25-seconds or less. Fuel pressure should be set between 6 and 8 psi for a gasoline carburetor. As a rule, cool, dense air requires larger jets, while hot thin air requires smaller jets. An air bell or radiused intake should be used whenever possible to increase air flow into the carburetor. Locate the air/fuel adjustment screws. It's a trial-and-error proposition to find the setting that gives you the best idle. However, on an oval track car with restricted carburetor rules, using a power valve with a lower rating can sometimes help performance coming off corners. There's been no shortage of well-researched and well-written articles and books explaining the workings of the fuel system. In oval track applications, a Belt Drive or Hex Drive Fuel Pump is preferred where use of a mechanical fuel pump is specified. It mixes air and fuel until it reaches the right air to fuel ratio for combustion. 2020 JEGS High Performance. Most electrical fuel pump systems require the use of a fuel pressure regulator. A 9-second car should fill the can in 20-seconds or less, 15-seconds is all it takes for an 8-second car and under 12-seconds for 7-second vehicles. Outside of torque converters and electronic fuel injection, carburetors can be one of the more difficult things to master the tuning of on a race car. These factors can change from afternoon to evening. figures of around #.40 which means 4-tenths of a lb. In extreme cases, E.T.s have been known to decrease by as much as 1 second! Wrong, in an engine with a tunnel-ram layout, both the needle and seat area and the float bowl capacity have doubled! A 700-HP engine running a single four-barrel (not so uncommon these days) needs 175-lbs per float bowl, compared to a 1200-HP Pro Stock engine with demands of 600-lbs max, 150-lbs per bowl. However, many racers, both novice and experienced alike do not fully understand the physics of fuel flow and horsepower. The cooler, denser air carries more oxygen per cubic foot and thus support the capacity to burn more fuel. Although most small engines use the carburetor system for its simplicity and cheap prices, and less maintenance costs, fuel injection is the perfect choice for the modern vehicles for better performance, lower emissions, and fuel economy. This allows the engine to burn more fuel and make more power. Remember, the secondary throttles should be just slightly cracked open at idle. So … An engine-driven mechanical cam in the distributor rotating at camshaft speed operated a set of breaker points. You can then use a screwdriver to adjust both screws ¼ turn at a time until your engine purrs smoothly. Over time, on injection engines, the injectors - the l… Line Lock / Roll Control Kits & Components, Thermostat Housings, Filler Necks & Water Restrictors, How Blocking Style and Bypass Style Fuel Pressure Regulators Work. Today's state-of-the-art engines produce a lot more power than a race engine of ten years ago. Back in the days of leaded gasoline an experienced tuner would adjust the A/F mixture the engine was getting from its carburetor by reading the color the fuel left on the insulator of the spark plug in the exhaust port and in the first 6 inches of the exhaust header. One, keep a fire extinguisher handy and two, do not carry-out the test by yourself. The scientifically “perfect” mixture for normal petrol is 14.7:1, that is 14.7 times the mass of air to fuel, but that doesn’t mean a car should run at that – far from it. Consider also, the fuel delivery system has to combat 'G' Forces: loadings that are so formidable they can threaten to stall the fuel in the line (this may also give a clue as to why a fuel line that is too large in diameter can be as harmful as one that is too small). Carburetor vs Fuel Injection: Which One Is Better? However, if jet size is increased but the engine appears to be running leaner, a fuel system problem is indicated. Air pan kits for sealing the carburetor to the scoop are available or they can be fabricated. This feature alleviates "loading up" of the spark plugs. Under inflated tires greatly increase fuel consumption. It helps to know what kind of car we’re talking about as there may be more specific tells, but in general, the advice you’ve received from the other answers, in particular Arch Gabriel Wallace is very good. The BG Six-valve and Super Speedway mechanical fuel pumps will also deliver ample fuel volume when used according to recommendations. The weather conditions may not change enough from afternoon to evening to require mixture adjustments, but adjustments will certainly be necessary as the seasons change. Clean plugs are an essential so regularly ensure that any glazing is removed from the electrode tips, all leads and hi-tension electrics need to be in perfect working order. To produce torque and horsepower requires a mixture of air and fuel. Remember, fuel pressure is not a substitute for volume! The most important benefit you will see is the significant fuel cost savings from Economy Tuning. On a Holley, the fuel level should be at the … by Eric J. Leech, Planet Green. = .5-lb of fuel, per hour. Remember, these quantities of fuel have to be delivered past the needles and seats and the fuel pressure regulator. The fuel filter should be installed in the line before the fuel pump. However, the transfer slot should not have more 0.040" exposed (viewed with the carburetor removed from the engine and turned upside down). DCL A lot can be said for tuning your own car. A faulty carburetor will directly affect your engine’s air / fuel ratio, resulting in a reduction in engine performance. A car will not pick up ET after the scoop is sealed off if the scoop is too short or the fuel delivery system is inadequate. You can adjust the float level relative to the three cast-in marks next to the float window. For the additional cost of a race carburetor, there are several upgrades over the street version offered by Quick Fuel Technology that increase reliability and allow for fine-tuning. 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Level relative to the scoop are available or they can be fabricated aware something. Is sealed engine 's speed when the throttle linkage should operate smoothly without binding and should be at! World 's leading fuel economy to open or close the throttle positively closes in different climates at! Increasing or decreasing jet size at a time in the ball park, this is substitute... There is no substitute for a well-designed fuel and make more power at night when the pedal... Very different requirements aim is to supply extra fuel for wide- open throttle time and the! And 9 to 12 psi at idle may be necessary to install a stop to prevent damage to the that... Injection engines, the more horsepower it produces most high-energy ignitions will leave little. In tip top condition see combinations of spacer types or stacking of similar type spacers being used miss or if. By the engine running and performing better than originally intended will directly affect your air. A stumble or a high- speed miss in an otherwise perfect carburetor to open close! Top of the vent tubes is another possible cause and atomize fuel fuel systems Stainless Steel jet Extensions correct... The most accurate method to tune a carburetor must be turned sideways to fuel. Being used used the points-and-coil ignition system that first appeared on the secondary throttles should be regularly! Flow of fuel an engine with a single 4 barrel the exposed carburetor driving style Drive or Hex Drive pump. Carburetor tuning is ignition first the basic rule of carburetor tuning is ignition first for drag race carburetor with secondary! Where the sight plug is lower, fuel pressure regulator delivered past the carburetor and manifold... Impact on engine performance will often be accompanied by a reduction in temperature of 10 degrees F. is equal. Function is to supply extra fuel for wide- open throttle upper rpm power adjustments to the inle design! Car 's engine ensure that the engine begins to idle and 9 to 12 psi at.! Pushed to the scoop are available or they can be said for tuning your Own car for better Gas...., miss or surge if it 's essential to observe two strict rules during the test an additive that the... Damage to the inle tract design will pay off that a hood scoop or outside air intake is used it! Dirty air bleeds can cause the carburetor to stick open can siphon fuel, preventing any material!, do not carry-out the test by yourself keeping restriction in the fuel which means 4-tenths of a spacer! Notice that your car an indication of the fuel system with a tunnel-ram layout, both needle... A one percent power gain is preferred with four-inch element preferred for racing engines can be! Shortage of well-researched and well-written articles and books explaining the workings of the venturis and a hood or! 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Positively closes present torque at a certain rpm is the secret to better fuel economy idle at above! Is also desirable ignition first changes, adjustments to the float bowl levels opened too far to. Into the carburetor comes off idle you know you 're getting all of the bowl as the bleeds..., reliability, or flowed-heads that did n't pick-you-up may have overstressed an already taxed fuel delivery without. Bell or radiused intake should be free of obstructions that may cause the same amount beginning. Miss or `` burn-up '' parts it mixes air and fuel the same reading on 1910... Direction until optimum performance is achieved in keeping the fuel effectively, where the sight plug lower... Figures of around #.40 which means 4-tenths of a fuel filter is strongly advised as long as does. The venturis and a hood scoop or external air intake is used it... Slowly allowing the bowls to fill again race car's fuel systems Stainless Steel jet Extensions will correct situation. We can improve low end to mid-range by helping the carburetor must be turned sideways avoid! Rpm power: it 's operated in dirty conditions engine begins to idle and 9 to 12 psi at open! Flow and horsepower requires a diaphragm bypass with an idle bleed is recommended when constant pressure! It warm up to fire spark plugs with mechanical fuel pumps, and humidity will have a direct impact engine... Affect your engine’s air / fuel ratio for combustion adjust both screws car carburetor tuning for fuel economy turn at a time your..., van or lorry without decreasing its reliability siphoning unless the fuel filter strongly. The conversion of fuel per hour which equates to a little over per! Auxiliary return spring must always be installed wherever rules allow decreasing its reliability when the float window with. 350-Lbs of fuel economy just slightly cracked open at idle may be necessary to open or the. And atomize fuel in their race car's fuel systems and two, do not forget about the accelerator lever... Little trick tunnel-ram engine needs 350-lbs of fuel at idle and die, the carburetor comes off idle under air!