CARBURETOR TUNING

Braswell Carburetion and TCR Performance set you straight

Words: David Zartman

If you’re a 4WD Toyota owner with a carburetor equipped engine, be it an OEM Toyota engine (20R, 22R, F, 2F etc) or a swapped small block V8, you’ll have to deal with problems that the EFI folks don’t. Not just changing jetting for altitude, erratic idling or cold starts, but even things common to wheeling like a steep hill climb or descent can cause unexpected problems. (In the Battle of Britain during WW2, German Me-109 fighters could escape from pursuing British Supermarine Spitfires by negative-G dives because they had fuel injection and the Spitfires were carbureted.) Not to mention cleaning, tuning, and rebuilding your carb.

Carbs do one basic thing: mix air and fuel into a mixture that your engine can burn, thus powering your vehicle through the action of your engine internals. Keeping yours in peak condition is important if you want smooth power delivery while in rocks, mud, tight trees or any other 4WD situation. A carburetor works on Bernoulli’s principle: the fact that moving air has lower pressure than still air, and that the faster the movement of the air, the lower the pressure. Generally speaking, the throttle or accelerator does not control the flow of liquid fuel. Instead, it controls the amount of air that enters the carburetor. Faster flows of air and more air entering the carburetor draws more fuel into the carburetor due to the partial vacuum that is created. Common carburetors are either “downdraft” (flow of air is downwards) or “sidedraft” (flow of air is sideways). We turned to DaveBraswell, owner of Braswell Carburetion. Dave is an acknowledged expert at all things carbureted, from NASCAR race cars, drag racers, circle track cars and yes, 4WD applications. We sat down with Dave over coffee and got the lowdown on carbs—what to do, what not to do, and when to do them. Then we talked with Tim Rodda, owner of TCR Automotive and Performance, for a no-BS chat on Toyotaspecific carb tech.

THE BRASWELL INTERVIEW

4WD Toyota Owner: When does a carb need to be completely rebuilt versus just tweaked and tuned? How do you know when to do it?

Dave Braswell: If the carb is properly cared for, meaning good filtration of both the air and the fuel, and the fasteners are kept tight and the accelerator pump cams and arms are cleaned and lubed (with moly dry lube) along with the throttle shafts, the service life is surprisingly long. It is a good idea to check the air cleaner often and inspect the air bleed jet to make sure they are clean and open. Most carburetor problems are from lack of hygiene rather than wear and tear.

4WDTO: It’s said that if you have cast-iron heads, you can run lean for more power. Is this a myth, or is it true? If so, how? Talk about heat in an engine can equal more power, supposedly.

Braswell: Maximum power is achieved with an air/fuel ratio slightly richer than stoichiometric (the chemically correct ratio). This is to insure that all of the oxygen molecules are consumed. Best economy is with a slightly leaner mixture to insure all the fuel molecules are burned. The material of the cylinder heads are made of does not change this. The thermal conductivity of aluminum is higher than that of cast iron, so there is less heat loss to the cooling system at a higher operating temperature. It is important to make sure the intake air to the engine stays as cool as possible. This will produce more improvement in performance than any one single item.

4WDTO: Please talk about float level adjustment: why it’s important and how to do it right.

Braswell: Float level adjustment is one of the most important and overlooked tuning tools. Before the float level can be properly adjusted, the fuel pressure must be correct. This may require the installation of a fuel pressure regulator. The pressure on today’s modularstyle carburetors (Braswell, BG, ProForm, QFT or Holley) should be between 4.5 to 6.5 PSI. Too much fuel pressure causes the fuel in the float bowl to become aerated, leading to poor performance. Fuel starvation at high RPM should be corrected by going to a larger needle and seat. The bowls we make (which fit most of today’s performance carburetors) have a glass window in the side. This makes fuel level adjustment very simple. Higher fuel level will provide a richer fuel mixture from off idle all the way through higher RPM range. It will sometimes lead to flooding and poor performance at low RPMs, while cornering or in off-road conditions. Low float level can cause leanness at high RPM and sometimes allow speed stumble.

4WDTO: 4WD Toyota owners often go up steep hills or down steep slopes. How can that affect carb performance and what can be done about it?

Braswell: Proper fuel pressure combined with float level adjustment. I’ll tootmy own horn and say that we produce two floats that work very well in off-road applications: the 16-3000 and the 16-3010. These were designed for road race use but have excelled in off-road application.

4WDTO: Discuss the importance of considering how much your engine head flows and how that fits into the overall tuning situation with the carb.

Braswell: Higher flowing cylinder heads will produce more power. If the port volume is kept low they will also produce a stronger signal to the carburetor. Basic fact: it takes air flow to make horsepower, period. The more power you produce, the more the carburetor has to flow. This is regardless of engine size.

4WDTO: How should carbs be adjusted if the driver knows he’ll be going up in altitude several thousand feet or more?

Braswell: Usually this will require the carburetor to be leaned down on the main jets. The idle and high speed air bleed jets should be increased and sometimes lowering the float level helps.

4WDTO: What’s the one thing one should NEVER do with their carb (besides smoke cigarettes around it!)

Braswell: Put grease on the accelerator pump cams. This might work well on the bench, but as soon as you go off road it will collect dirt and quickly wear out these parts.

TCR PERFORMANCE TOYOTA CARB TECH TALK

Tim Rodda, owner: “In my opinion the 22R carb is a refined, durable, and highquality Toyota carburetor and provides the best all around drivability, fuel economy, emissions and performance. Of course, it needs to be in good operating condition. I’d opine there is no true replacement carb for this. Out of the box it meets those basic goals.” The typical issues related to a poorly operating 22R carb are as follows.

–Black smoke or fuelfouled spark plugs is a ruptured auxiliary accelerator pump diaphragm (21675- 35510)

–No idle: blown engine fuse or failed idle-cut solenoid

–Vapor lock: never use a metal carburetor-to-cylinder head pump spacer

–Poor gas mileage or failed emissions: Worn main fuel jet (90999-41114 #14, 41116 #16, 41117 #17, 41119 #19, 41122 #22)

–Damaged idle mixture screw (21271-35010)

–An incorrectly operating emission control ECU can produce a severe fuel surge/ idle cut situation just above base idle through primary fuel operation. The best all-around correction is to add a jumper wire from the black/white or white wire (for the idle cut solenoid to chassis ground.) This effectively defeats the ECU function, but be aware, you may not pass a “cruise condition” tail pipe emission test.

–Dirt and contamination: damaged/missing air cleaner stud (90116-06020), wing nut (90175-06003), air cleaner-to-carb base seal (178489-35010), air filter (17801-41090) or fuel filter (23300-34100).

–Poor or incorrect intake manifold fuel distribution: Always use the carb-to-intake manifold spacer/gasket with the metal tongue located on the spacer primary side.

MODIFYING A 22R CARBURETOR

–“You can convert a 20R engine to the stock 22R carburetor with adapter #16- 1105

–The 22R main jets will satisfy 85-percent of mildto- moderately modified 22R engines up to 200 C.I. Stroker mills

–This carb easily converts to Holley-brand main jets

–The secondary fuel A/F ratio is changed by raising or lowering the secondary fuel needle by carefully turning the crimped adjustment nut

–The idle and low speed air correction is modified with the use of a “jet” drill bit set. Always start small and retest, and always inspect or replace the small sealing O-ring

–A racing 22R carb can exceed 360 cfm with proper components and tuning, such as a modified primary booster, reshaped venturi, and more

–For idle speed calibration, the primary throttle blade should never exceed one full turn of the idle base screw from a fully closed position (to meet the idle requirements of any given high-performance engine.) I recommend starting with a 5/64” drill bit and drill the primary throttle blade. This helps with additional idle speed, and helps keep bogging, hesitation, and lean fuel conditions during deacceleration-to-reacceleration driving conditions.” And what about hardcore off-road conditions? “For really rough off-road conditions, minimize the float drop adjust to help prevent the fuel inlet needle from sticking closed.”

Last words? “In order to tune/calibrate a carb to any degree of accuracy an air/fuel mixture meter/O2 sensor combination is mandatory. A vacuum gauge and infrared temperature gun can also be very beneficial.”

WHO IS BRASWELL CARBURETION?

Name of company: Braswell Carburetion

Founder: Dave Braswell

Location: 7671 N. Business Park Drive, Marana, AZ 85743-9622

Phone and website: (520) 579-9176, www.braswell.com

History of company: A specialty manufacturing company producing high quality carburetors and replacement component parts for carbureted motorsports. Started in 1968 producing modified Holley and Weber carburetors. They do complete design, engineering, development and manufacturing services for professional race teams around the world. Braswell products are sold under their own name and sold under private label by many other firms. What new 4×4 products do you have coming out or now, especially those that work on Toyotas or the small block V8s most commonly found in Land Cruisers? Our Severe Duty Fuel Chute fuel bowl kits are great for serious off-road use. They feature our own custom molded floats and spring loaded needle and seats. These high-quality aluminum die castings feature internal ribs to control fuel slosh and Fuel Chute delivery shape, both of which are covered by U.S. and foreign patents. What is your favorite Toyota 4×4? “A 4WD Tundra SR5 will be my next vehicle purchase.”

A LOOK AT TCR PERFORMANCE

Name of company: TCR Automotive and Performance

Founder: Tim Rodda

Location: 4725 E 22nd St., Tucson, AZ 85711

Phone and website: (520) 747-0563, www.toyotaperformance.com

History of company: 28 years as a professional technician and fabricator. The last 14 years as an owner. “Real performance on the trail is my priority. I have no desire to develop a product, then be forced to have China produce it in order to make a buck.” Only authorized dealer for L.C. Engineering, and they give input on LCE’s products. He also builds engines for D.O.A. Racing Engines. Dealer for Downey Offroad, Marlin Crawler, JE Pistons, CP Pistons, Pauter Machine, and more. What Toyota 4x4s do you own? “I have a 1984 4×4 truck, 2005 Sequoia, and a 1991 2WD Sportsman-class desert race truck.”

BASIC CARBURETOR TERMINOLOGY

Running lean: Not enough fuel mixed with the air

Running rich: Too much fuel mixed with the air

Metering Block: The carburetor’s nerve center, where everything comes together. Jets, which actually control how much fuel is going into the metering block, are found here, as are the emulsion holes. Fuel passes into the metering block, via the jets, mixes with air from the emulsion holes, and passes through boosters to be fed to the engine.

Venturi or barrel: Narrow spot (also called a throat) in center of carb in which a vacuum is created. Most carbs have at least two barrels, with four barrels being common in larger displacement engines to accommodate the higher air flow rate. Multibarrel carburetors can have non-identical primary and secondary barrels of different sizes and calibrated to deliver different air/fuel mixtures. Vconfiguration engines, with two cylinder banks fed by a single carburetor, may be configured with two identical barrels, each supplying one cylinder bank. Similarly, in the widely seen V8 and 4-barrel carburetor combination, there are often two primary and two secondary barrels.

Butterfly valve: A rotating disc that can be turned end-on to the airflow, so as to hardly restrict the flow at all, or can be rotated so that it almost completely blocks the flow of air. This valve controls the flow of air through the carburetor throat and thus the quantity of air/fuel mixture the system will deliver, thereby regulating engine power and speed.

Jets: Fuel is introduced into the air stream through small holes at the narrowest part of the venturi. Fuel flow in response to a particular pressure drop in the venturi is adjusted by choosing small brass screws with finely calibrated holes, referred to as

jets, into the fuel path.

Float chamber: To ensure a ready supply of fuel, the carburetor has a “float chamber” (or “bowl”) that contains a quantity of fuel ready for use. The level of fuel maintained in the float bowl can be adjusted by a setscrew (“needle”). This is usually a critical adjustment–the rule of thumb for the common Chevrolet small block V8 used to be that the float bowl fuel level and the distributor points gap were the only two critical adjustments on the engine. The proper adjustment is indicated by lines scribed into a window on the float bowl, or a measurement of how far the float hangs below the top of the carburetor when disassembled.

OEM TOYOTA 20/22R CARB SPECS

Stock airflow in 20R (2.2L engine) carb: approx 200 CFM

Stock airflow in 22R (2.4L engine) carb: approx 290 CFM

22R main jets commonly available: #108 to #203

Common non-California main jet is #114 to #118

Tuning your carb will improve gas mileage and power output. This pickup is a 20R 1979 model and literally fresh off the boat. Photo courtesy Toyota USA Archives.

Here’s a closeup of the carb found on the 22R engine. This one is from 1982, and from the mud in the engine bay we’d say it’s seen some recent off-road action. The 22R carb flows approximately 290cfm, while the 20R does 200cfm.

Although not often seen in the US, a Nikki carb is found in Toyota 4Y engines. This photo shows the float bowl with 90- degree fuel inlet and vapor return tubes above it.

By | 2016-12-06T04:57:33+00:00 December 6th, 2016|Categories: Articles|Tags: |0 Comments

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