How to Choose the Best Carburetor for Your Engine

Introduction

When it comes to classic cars, trucks, or performance builds, the carburetor is one of the most important components. It directly controls how fuel and air mix before entering the combustion chamber. Choosing the wrong size or type can lead to poor drivability, bad throttle response, and wasted fuel.

In this guide, we'll explain:

What a carburetor is and how it works
The difference between a 2-barrel carburetor vs. 4-barrel carburetor
How to calculate the right carb size (CFM)
How to adjust a carburetor for better performance
Which options are the best carburetor choices for street and race use

We’ll also highlight some proven options from Evil Energy, such as their 600 CFM 4 barrel carburetor.

What Is a Carburetor?

A carburetor is a mechanical device that mixes air and fuel in the proper ratio for combustion. Before electronic fuel injection became standard, carburetors powered nearly every gasoline engine.

What Does a Carburetor Do?

Mixes air with atomized fuel
Adjusts fuel delivery based on throttle input
Keeps the engine stable at idle, acceleration, and high RPM

How a Carburetor Works

Carburetors use the Venturi effect: as air rushes through a narrow passage, pressure drops and draws fuel into the airstream. The faster the airflow, the more fuel gets mixed in, delivering more power.

2 Barrel vs 4 Barrel Carburetor

2 Barrel Carburetor

Simpler design, with two venturis
Common on smaller displacement engines or economy setups
Good for light street driving and fuel efficiency

4 Barrel Carburetor

Four venturis for more airflow
Delivers better performance, especially at higher RPMs
Popular for small-block and big-block V8 engines
Can be configured as a vacuum secondary (street-friendly) or mechanical secondary/double pumper (performance-oriented)

If you want a balance of drivability and performance, a 600 CFM 4 barrel carburetor is one of the best carburetor choices for a Chevy 350 or similar V8.

How to Choose the Right Carburetor Size (CFM)

Carburetor size is measured in CFM (Cubic Feet per Minute) — the amount of air it can flow. Choosing the right size is critical for drivability, throttle response, and overall performance. Bigger is not always better.

Formula: Engine Displacement × Max RPM ÷ 3456 = Required CFM(100% VE)

Example (100% VE):

350ci engine × 5500 RPM ÷ 3456 ≈ 557 CFM → best match is a 600 CFM carburetor.

Adjusting for Street vs. Race Use

Most street engines don’t run at 100% volumetric efficiency (VE). A more realistic number is 80–85% VE.

Example at 85% VE: 350ci × 5500 ÷ 3456 × 0.85 ≈ 474 CFM → a 500–600 CFM carb is ideal.

High-performance or race engines (with better heads, cam, exhaust) may be closer to 95–100% VE, so the higher calculation applies.

Quick Tip

Slightly undersizing the carb often gives better throttle response and drivability.
Slightly oversizing may work for all-out racing, but can hurt street manners.

Don’t want to calculate? Use the official CFM calculator in 30 seconds and pick the right 600 / 650 / 850 CFM option. Try It Here

Carburetor Choke (Cold Start Aid)

The choke helps the engine start and run when it’s cold by restricting airflow and enriching the mixture. Some carburetors have a choke, some don’t. Whether you need one depends heavily on the climate and application.

Common Types

Electric Choke
- Connects to a 12V source, automatically heats and opens.
- Simple and hands-free operation.
- Best for daily drivers and colder climates.
Manual Choke
- Operated by a cable or lever inside the car.
- Gives the driver full control over cold-start behavior.
- Preferred by performance users who want precision.
- Personal note: I prefer manual choke since it gives complete control.
No Choke
- Simplified, race-oriented design.
- Can be difficult to cold start, requires throttle “babysitting.”
- Best suited for racing or warm climates.

Selection Tips

Cold climates (e.g., Alaska): Electric choke strongly recommended.
Warm climates (e.g., Florida): Choke is often unnecessary.
Performance builds: Manual or no choke is common, since automatic control may not suit modified engines.

Carburetor Types

Vacuum Secondary (Best for Daily Driving)

Opens secondary barrels only when the engine demands more air
Smooth power delivery, ideal for heavy vehicles or automatics
Forgiving if you oversize slightly

Great choice: 600 CFM Vacuum Secondary 4 Barrel – pre-jetted, plug and play.

Mechanical Secondary / Double Pumper (Best for Performance)

All four barrels open immediately at WOT (wide open throttle)
Snappy throttle response, ideal for lightweight cars, manual transmissions, or race setups
Requires a stronger fuel system

Great choice: 650 CFM Mechanical Secondary 4 Barrel – tuned for street/strip builds.

High Flow for Big Engines

Larger venturis and throttle bores for high-RPM horsepower
Perfect for big-block or high-revving small-blocks

Great choice: 850 CFM Mechanical Secondary 4 Barrel.

Quick Buy Guide

Driving Style / Vehicle	Recommended Type	Example Carburetor	Key Features
Daily driver, automatic, heavy vehicle	Vacuum Secondary + Electric Choke	600 CFM 4 Barrel	Smooth response, easy cold starts
Mild performance, manual trans, gears	Mechanical Secondary + Manual Choke	650 CFM 4 Barrel	Snappy throttle, pre-jetted #70/#74
High RPM, race builds, big engines	Mechanical Secondary + Large Bore	850 CFM 4 Barrel	1.56-inch venturi / 1.75-inch throttle plates

Carburetor Adjust – How to Tune It

Tuning a carburetor is just as important as picking the right size.

Steps:

Warm up the engine to the operating temperature.
Locate idle speed and mixture screws.
Adjust mixture screws slowly until you find the smoothest idle.
Fine-tune the idle speed screw to the recommended RPM.
Check spark plugs – tan/brown means the carb is properly tuned.

Tip: Use a vacuum gauge for the most accurate carburetor adjustment.

How to Install a Carburetor

If you’re upgrading your classic ride with a new carb, don’t worry — the process is easier than it looks. In this video, we’ll walk you through how to install the Evil Energy 600 CFM 4 Barrel Carburetor step by step. Whether it’s your first carb swap or you’ve done a few before, you’ll see exactly how to remove the old unit, bolt on the new one, and get your engine running smoothly again.

Fuel System Add-Ons

To keep your carburetor healthy and fuel delivery stable, consider:

Inline Fuel Filter – keeps debris out
Fuel Pump – supports high CFM carbs
PTFE Fuel Line Kit – resistant to modern ethanol fuels

Bundle these with your carb to save time and keep the system clean. Shop Fuel System Add-Ons

Carburetors

EVIL ENERGY carburetors deliver the right balance of airflow and fuel for street and performance builds. Available in multiple sizes and styles to match your engine needs.

Learn More

FAQs

Q: What’s the best carburetor for a Chevy 350?

A: A 600 CFM 4-barrel carburetor is the sweet spot for most small-block Chevy 350 builds. It balances drivability, throttle response, and performance for street use.

Q: How do I adjust a carburetor for better mileage?

A: Tune the idle mixture screws slightly leaner (but not too lean) and check results with a vacuum gauge. Proper carburetor adjustment helps improve fuel economy without sacrificing drivability.

Q: Is a 2 barrel carburetor still worth it?

A: Yes, if you’re restoring a stock or economy-focused engine. A 2 barrel carburetor is simple, reliable, and efficient. But for most V8 builds, a 4 barrel carburetor delivers more flexibility and power.

Q: What size carburetor do I need for a 305 Chevy?

A: Typically, a 500–600 CFM carburetor works well for a 305ci small-block. Going too big will hurt low-end response, so stick to a properly sized 4 barrel carburetor for the best results.

Q: Should I choose a vacuum secondary or mechanical secondary carburetor?

A: For daily drivers and heavier vehicles, a vacuum secondary carburetor provides smoother power delivery and better street manners. For lightweight cars, manual transmissions, or racing, a mechanical secondary (double pumper) is the better choice.

Q: Do I need an electric choke or manual choke?

A: If you live in colder climates or want easier cold starts, go with an electric choke carburetor. If you want more control for a performance application, a manual choke carburetor may be preferable.

Q: How often should I clean or rebuild my carburetor?

A: Most carburetors should be inspected and cleaned every 12–18 months, especially if the vehicle sits for long periods. Ethanol fuel can leave deposits, so adding a fuel filter and running clean fuel is important.

Q: What’s the difference between a stock replacement carburetor and a performance carburetor?

A: A stock replacement carburetor prioritizes reliability and fuel economy, while a performance carburetor (like a 650 or 850 CFM 4 barrel carb) is tuned for airflow and horsepower at higher RPMs.

Q: Can I upgrade from a 2 barrel carburetor to a 4 barrel carburetor?

A: Yes, but you’ll need the correct intake manifold designed for a 4 barrel carb. The upgrade usually provides better throttle response and horsepower potential.

Q: What’s the best carburetor for towing with a Suburban or truck?

A: A 600 CFM vacuum secondary carburetor with an electric choke is often ideal. It offers smooth power delivery and reliability under load.