One Day Project: Rebuild Your Carburetor

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Engines and Components

Nina Russin

November 16, 2016

Nina Russin

November 16, 2016

Think of the carburetor - opens in new window or tab. as a mixing bowl for your car’s engine, delivering the proper proportions of air and fuel to the intake manifold based on driving conditions. All carburetors have seven circuits for this purpose, delivering rich fuel mixtures for power and acceleration—and leaner mixes during idle, off-idle, and deceleration.

When to Rebuild

How do you know if your carburetor needs rebuilding? Usually there’s a dip in performance: hesitation upon acceleration, engine missing at cruising speeds, or a small chug when you tip into the throttle when the carburetor transitions from the idle to off-idle circuits.

Over time, small jets inside the carburetor can become clogged. The best way to clean them is to disassemble the carburetor and rebuild - opens in new window or tab.. While ideas of reassembling all of the small screws and linkages might seem daunting, it’s actually fairly simple, since all carburetors have the same basic design: a housing, air horn, throttle valve, venturi, discharge tube, and fuel bowl.

carb-kit-800 — Holley Carburetor Rebuild Kit

What You Need

Basic hand tools - opens in new window or tab., and a clean, well-lit table surface
Shop rags - opens in new window or tab.
Carburetor cleaner - opens in new window or tab. to soak the venturi cluster
Smartphone camera and pieces of cardboard: use the camera to photograph the disassembly and put the bolts and linkages on pieces of cardboard in the approximate locations you removed them from to make reassembly easier.
Carburetor rebuild kit - opens in new window or tab.: contains the gaskets, seals, accelerator pump, needle valve, and seat necessary to rebuild along with an exploded drawing for reference. If you’re not used to using exploded drawings, a shop manual will contain more detailed instructions.

Fear Not the Four Barrel

While logic might dictate that a four-barrel carburetor is more difficult to rebuild than a one-barrel unit, that’s not necessarily the case. The Rochester Quadrajet - opens in new window or tab. is easy as pie to rebuild while some Carter - opens in new window or tab. one barrels are super finicky.

quadrajet-800 — 1968 Pontiac 400 428 Quadrajet Carburetor

Making Adjustments

One of the biggest challenges in rebuilding older carburetors is that the pot metal body warps. When this happens, it can cause leaking around the base and throw off the linkage adjustments. Although many sources recommend discarding a carburetor and replacing it with a new unit, it is possible to straighten out the pot metal in a home oven. This article - opens in new window or tab. by Matt Joseph explains how.

While the rebuild kit serves as a basic guide for linkage adjustments and tolerances, you may need to play around with the adjustments once the carburetor is back on the car, since linkages on older carburetors tend to warp.

Simple Performance Fixes

Diagnose and fix the following performance problems without disassembling the carburetor:

Air leaking around the base of the carburetor: this can cause a variety of performance problems such as engine surging and stalling. To diagnose, squirt a little dish washing liquid around the base of the carburetor and let the engine idle. If you see air bubbles, you probably have a leak, possibly caused by a cracked base plate.

Bad float: the float that controls the fuel level in the fuel bowl is made of plastic that can dry out and become porous. Replacing it is relatively simple and doesn’t require complete disassembly.

Idle screws out of adjustment: while some idle problems come from clogged idle circuit passages, adjustment of the idle screws might fix an overly lean idle.

Stuck choke valve: chokes often stick in the cold weather when tiny bits of humidity freeze and prevent the butterfly valves from closing. Open up the air cleaner, push the valve shut manually and the problem is solved.

About the author

Nina Russin

Nina Russin is an ASE certified automotive technician and writer who has been covering the automotive industry for 30 years. She was a weekly automotive columnist for the Chicago Sun-Times for 10 years, and a contributor to AutoWeek, Automobile Quarterly, Collectible Automobile, Cycle World, and AAA Arizona Highroads Magazine. Russin is co-founder and president of Active Lifestyle Vehicle of the Year, an annual competition.

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This article is meant to provide general guidance only. Automotive maintenance, repair, upgrade, and installation may depend on vehicle-specifics such as make and model. Always consult your owner's manual, repair guide for specific information for your particular vehicle and consider a licensed auto-care professional's help as well, particularly for advance repairs.