Think of the carburetor 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. 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.
Holley Carburetor Rebuild Kit
What You Need
130-Piece Tool Set & Case Auto Home Repair Kit
- Basic hand tools, and a clean, well-lit table surface
- Shop rags
- Carburetor cleaner 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: 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 is easy as pie to rebuild while some Carter one barrels are super finicky.
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 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.
See Car & Truck Carburetor Rebuilt Kits for sale on eBay.
