Setting Idle Mixture and Speed Tips
The engine should be functioning at its optimal temperature. To establish a starting point, lightly seat the idle mixture screws and back them out 1-1/2 turns. Slowly adjust the mixture screws in or out as needed while the engine is running to achieve the optimal idle quality. Repeat the process once more. The first adjustment is coarse, while the second is a final fine one.
If the idling quality cannot be correctly adjusted, or the idle mixture screws cannot be backed out far enough to achieve adequate adjustment, the cam may not be pulling enough idle vacuum, and the idle circuits may have to be modified.
The primary butterflies being set too far open inhibits the idle mixture screws from managing the idle quality, which is a typical cause of lack of flexibility in idle mixture screws. The butterfly openings on both the primary and secondary sides should be adjusted evenly while establishing idle speed. However, the transfer slot should not be exposed to more than 0.040 inches when the carburetor is removed from the engine and flipped. Secondary adjustment is made with a screw accessible from the carburetor's underside.
At idle, the secondary throttles should be slightly open. Secondary throttle position at idle can be altered even on carburetors with a non-adjustable secondary idle mixture. Due to the cam configuration, it may be essential to open or shut the throttle adjustment. Finding the setting that offers you the best idle is a trial-and-error process.
As a starting point, consider opening the main and secondary butterflies to the same degree on engines that idle at or above 1000 rpm. Start with the main butterflies open approximately 0.020 inches, with the secondary butterflies positioned at the bottom of the transfer slot for engines that idle below 1000 rpm. Then, change the idle adjustment screws until the idle is steady and smooth.
Adjusting the Carb Jetting
If the carburetor is utilized in the specified application, jetting should be reasonably close whether you have a CCS Performance or a standard HOLLEY® carburetor (or a flow-modified CCS type). Increase or reduce the jet size by two numbers (primary and secondary) for optimal performance. Continue to increase or decrease the jet size as long as the performance improves.
ET or lap times will start to fall at some point, indicating that the mixture has been adjusted past the optimal air/fuel ratio. After that, change the jet size to the other direction one at a time until you reach optimum performance.
Always jet for performance, not for the color of the spark plug. The majority of high-energy ignitions leave minimal residue on the plugs. Attempting to "read" spark plugs in a drag vehicle is a waste of time since the plugs can remain bone white. The plugs will color in an oval track vehicle, but it will take longer with a high-energy ignition.
If the engine is running a bit hot, increasing the jetting size by one or two will ease the lean situation without sacrificing performance since the excess fuel will be burned off by the ignition, and the engine will cool. A fuel system issue is indicated if the jet size is raised yet the engine appears to be operating leaner. If a traditional ignition system is utilized, jetting for maximum performance is still recommended, but the plugs will become a tan color after a short period.
Problem-Solving
A lean engine will pop, miss, or surge, while an extremely rich state can also create the same issues. Cool, thick air, on the other hand, needs bigger jets, and hot, thin air necessitates smaller jets. When a carburetor spacer is added or removed, a camshaft, cylinder head, or intake manifold is changed, and the carburetor must be returned to get optimal performance.
Extensions
Another issue that causes a stutter or hesitation is when the secondary jets become exposed, which no amount of accelerator pump tweaking will fix. This happens when a car accelerates to the point that the fuel in the secondary bowl is pushed up against the back wall, exposing the jets due to G-force loading.
This can be remedied with CCS Custom Jet Extensions. When installing jet extensions in a carburetor with a secondary power valve, the secondary power valve must be removed and the hole covered. The size of the jet must then be adjusted correspondingly.
Pump Circuitry
Even if the jetting is in the ballpark, there is no assurance that the performance will be ideal. The performance will suffer if the accelerator pump nozzle or squirter diameter is wrong. The accelerator pump nozzle diameter may be too big if a car is slow during the start of acceleration. Another sign is if a plume of black smoke pours out of the headers when a drag car departs the starting line or an oval track car comes around a turn.
Another probable reason is fuel pouring from the vent tubes. Running a rubber hose from one vent tube to another with a slot cut at the top of the hose solves the problem. Trial-and-error testing is used to determine the optimal squirter diameter. To get the best results, simply change the size up or down.
Accelerator Pump Lever Adjustment
Don't forget to adjust the accelerator pump lever. The pump lever should be set for oval track use so that there is no play in the pump linkage when the throttle is closed. When the carburetor comes off idle, this will ensure that there will be no lean stumble. When tuning an accelerator pump for best performance off the corner, reducing the pump volume and discharge rate is common rather than increasing them.
Drag racing necessitates a somewhat different strategy. The pump lever override spring should be set such that fuel begins to discharge through the nozzle at an engine rpm lower than the launch RPM for the most difficult starting line launch with a foot brake. If the car is leaving the starting line at 5000 RPM, the accelerator pump shot should begin at 4700-4800; if the car is leaving at 1800 RPM, the accelerator pump shot should start at 1500.
The trick is to ensure that the accelerator pump system has no slop below the starting line RPM so that the pump shot is not "used up" below that RPM. Although setting the accelerator pump as stated will cause a lot of slop in the pump linkage at idle, causing a stumble when driving in the pits, the car will exit the track faster. Drag vehicles with a manual shift or transbrake, which launch from the starting line with the carburetor wide open, require the same adjustments as oval track cars.
Float Level Adjustment
When replacing the gasoline bowls or building a carburetor, adjust the float to be about 0.450 inches from the top of the bowl in line with the bowl screw bosses when the bowl is upside down. This "dry" setting allows you to get in the ballpark.
Recheck the float level with the engine running, and the sight plugs out. As the gasoline seeps out, it should just moisten the outside of the bowl. The fuel level should be somewhat greater on the secondary side, where the sight plug is lower. The huge sight glass windows on CCS carburetors allow float level adjusting without allowing gasoline to escape from the float bowl. Adjust the float level to one-third of the way up the float window.
Power Valve Tuning
The power valve's job is to provide more fuel when the throttle is wide open, and the load is high. The power valve opens and enriches the main circuit by around six to ten jet sizes when the manifold vacuum falls below the vacuum level imprinted on the power valve. This happens when the engine is under extreme stress, such as full throttle.
Under engine idle vacuum, the power valve number should be at least 1.5-2.0 in/hg. A 6.5 power valve will be a reasonable initial choice if an engine generates 8.0-9.0 in/hg of vacuum. Using a power valve with a lower rating can cause the enrichment to be delayed and create reluctance. Using a power valve with a lower rating in an oval track vehicle with carburetor restrictions, on the other hand, might occasionally assist performance coming out of turns.
To avoid fuel starvation, every drag racing carburetor with a secondary power valve must be adjusted sideways. As fuel is forced to the back of the float bowl, the power valve, which is higher than the jets, is the first to be uncovered. The carburetor must be moved sideways because there is no way to extend the power valve.
Throttle Plates and Linkage
When the throttle is pushed to the floor, the carburetor must be wide open to produce maximum performance. As a result, the throttle opening should be checked frequently, especially after any substantial modifications in the engine compartment. If the throttle plates do not reach the wide-open position, or if they are dragged past wide open, maximum air flow cannot be obtained.
The throttle linkage should be clear of impediments that might cause the carburetor to stick open and should work smoothly without binding. To ensure that the throttle shuts positively, an additional return spring must always be installed. A stop may be required to prevent the carburetor from opening too much and causing damage to the linkage.
Climate Changes and Performance
Temperature, barometric pressure, and humidity all affect air density, which directly influences engine performance. Adjustments to the fuel mixture are frequently required when the air density varies. These variables might shift from the afternoon to the evening.
Everyone knows that as the air cools at night, the engine produces greater power. Cooler, denser air carries more oxygen per cubic foot, allowing more fuel to be burned. The weather may not change sufficiently from afternoon to evening to need mixture modifications.
However, as the seasons change, adjustments will undoubtedly be required, such as fuel mixture modifications when traveling to tracks at different temperatures or elevations. When tuning for optimal performance, these aspects must be considered.
Tuning with Spacers
Spacers and plenum dividers make it simple to alter the intake tract's shape and characteristics, as well as its interaction with the carburetor. For oval track applications, adding a plenum divider to an open plenum manifold can balance the left to right fuel distribution. This is especially useful on alcohol engines.
The use of spacers between the carburetor and the intake manifold can have a big impact. A four-hole spacer can increase low-to-mid-range performance by assisting the carburetor in drawing and atomizing fuel. The plenum area is increased by using an open center spacer, which can help with mid-range and upper-rpm power. Using combinations of spacer types, as well as stacking of similar type spacers, are not rare.
Only when running a test and tune session on the exact engine combination can the results of any spacer or combination of spacers be measured. This data may be extremely beneficial when tuning for maximum HP or changing power characteristics to fit a certain track environment.
Routine Maintenance
A carburetor must be kept clean for consistent performance. Every week, spray the air bleeds with carburetor spray or WD-40. Dirt and colors in the fuel block up the air bleeds. In an otherwise excellent carburetor, clogged or unclean air bleeds might cause a stumbling or a high-speed miss.
Use this little trick when putting your car up for the winter. Spraying WD-40 generously down the venturi while the engine is spun over with the ignition off and the throttle open will leave a thin mist of protection on the valve seats and cylinders, preventing corrosion. Finally, your carburetor should be repaired once a year at the very least and more frequently if it's used in unclean conditions.
Alcohol Tips
Alcohol-fueled applications need more maintenance than a gasoline-fuel system. Alcohol should not be left in the fuel system or carburetor for a long period since it is corrosive.
Draining and cleaning the whole fuel system, especially gasoline, is part of proper maintenance. Flushing the system and adding gasoline to the fuel cell allows the pump to pull fuel via the lines and the carburetor, which is the most typical approach.
Because alcohol carburetors are significantly richer than gasoline carburetors, the system is very thoroughly cleansed when the engine starts to idle and die. If your sanctioning body allows it, apply a fuel additive that lubricates the fuel system for further protection during racing.