Tuesday, February 1, 2011

Basic Carb Rebuild Guide

The article featured on this page is from the March 2011 issue of Auto Enthusiast Magazine.


Your Basic Carbs

Steps to rebuilding or repairing a carburetor

Story Earl Duty

I’ve been rebuilding and repairing carburetors since 1964 and over the years I’ve been asked (by numerous car folks) one simple question; “Can the average car guy rebuild a carburetor at home?” The answer — in most cases — yes. Note I said in most cases.

Just as there are many variations to the term restoration, there’s any number of variables to carburetor repairs. Let’s start with a simple question. Does your carbureted vehicle have a hesitation on acceleration — poor engine idle, backfiring through the carburetor (especially on hard acceleration), or poor fuel mileage? Then the following information will give you the basics of rebuilding a carburetor, where cleaning of the unit and the installation of a minor carb kit should more than likely cure those problems.

Can I cover all carburetors and their associated gremlins in the span of one story? Of course not – one story cannot cover every carburetor. But if your carburetor has the normal age related woes, then this info should get you up and running again. First of all – and I can’t stress this enough – how’s your memory? Installing a rebuild kit in any carburetor requires that somehow you remember where all the parts and tiny pieces go. A little brain-fade on your part maybe, then pull out the digital camera (or a note pad) and document the process from the very beginning.

During this carburetor basics story, I’m going to use any given number of different carburetors for demonstration purposes. And in all my years of rebuilding these air/fuel dispensers, I’ve learned one thing: A carburetor, is a carburetor, is a carburetor. They all work on the same principle, they’re just physically different.

Visually inspect the unit. Do you see any broken parts such as linkage, the choke system or throttle shaft? Is the throttle shaft binding? If so, stop right there and find a company that offers carburetor overhauls and/or rebuilt units. Check throughout your current issue for vendors. If you find nothing broken or binding on the carburetor and your vehicle simply runs bad (due to the aforementioned carburetor symptoms) then in most cases a minor rebuild will fix the problems.

Tools you’ll need

Basic hand tools, wrenches, screwdrivers, compressed air (nice to have, but optional), ratchet and sockets plus a metal parts cleaning pan are needed. Caution: have proper ventilation, wear eye protection and use chemical resistant gloves when using compressed air or any cleaning chemical.

Due to the fact most carburetors have a gum and varnish buildup on the interior and exterior, spray cans of carburetor and/or choke cleaner work well for cleaning the parts (most carburetors require two 16-ounce cans). I’ve found that brake cleaner in aerosol cans not only cleans well, it evaporates quickly.

Need parts? Rebuild kit, choke spring, floats, etc.? Throughout this magazine you’ll find vendors offering parts for your project. Tip: have those parts ordered in the early stages of disassembly.

The basics

Start by removing all upper bowl cover screws and attaching linkage. Be sure to record or document their locations for reinstallation. Remove the float and test. After the float has been tested, locate the carb ID numbers and order parts; they can be either on a tag attached to the unit, stamped on the bowl cover, or stamped in the base (where the throttle shaft is located). If all else fails (no tag, no numbers visible, etc.), when ordering the repair parts, have available the year, make, model and engine size of the vehicle.

If the float checks out OK, or you have a replacement, continue with the teardown by removing the lower base-to-bowl screws (if equipped) and record their locations. Remove any rubber parts from the carburetor. With everything disassembled from the carburetor and neatly laid out on the workbench, you’re ready for clean up.

Place each separate component of the carburetor in the metal drain pan and using proper eye protection, spray with carb cleaner until gum, varnish, and dirt are removed. Again, using proper eye protection and compressed air, blow out any and all orifices.

When a carb main jet is impossible to remove or in the absence of compressed air, I use the supplied nozzle extension that comes with the aerosol can of carburetor cleaner to remove gum, varnish, and debris. Caution: proper eye and skin protection is mandatory due to the fact this chemical (under pressure) can blow back into your eyes and/or onto exposed skin! I have also used a small piece of stiff wire to verify clean passages.

Assembly

Make sure to match new gaskets with the old originals to guarantee exact fit. The proper float level is critical to any carburetor, so follow directions supplied with the rebuild kit. It’s also a good idea to soak any new leather accelerator pump in gasoline just prior to installation.

I personally like to paint a carburetor purely for the aesthetics. Also, when painting any carburetor parts it’s extremely important to have those parts spotless and the metal warm to the touch (not hot). A light coat is all that’s necessary. A good way to warm the metal is with a hair dryer. The color I use for factory aluminum look is “Duplicolor Aluminum,” part # DE 1615. The gold paint I use is “Duplicolor Instant Gold” and to paint a cast iron carb base is “Duplicolor Cast Coat Iron.” The linkage and retaining screws get painted with “GM Duplicolor Light Gray EDSGM435.” These paints can be purchased at most well-stocked auto parts stores.

Before you reconnect the fuel line, clean out the line with compressed air (or spray carb cleaner) and install an in-line fuel filter. What’s the point of going through all this and then re-introducing dirt back into the carburetor? Will the basics I’ve listed solve any and all carburetor problems? No. But at the very least, it’s a good starting point. If for any reason you have apprehensions about taking on a carburetor rebuild, don’t start it. Purchase a rebuilt unit from one of the many suppliers located throughout this magazine.



1 A carburetor with miles and time on it will typically have a gum and varnish buildup (inside and outside).

2 In a perfect world carburetor ID numbers will be clearly stamped on the carburetor base, on a tag, or top cover.

3 If you hear a sloshing sound by shaking a brass float close to your ear it’s defective and needs replaced. Note the gas being squeezed out of this float.

4 If you want to double-check a brass float, submerge it in hot tap water (held by needle nose pliers) and watch for air bubbles.

5 In any given number of carb rebuilds, I’ve used small stiff wire to clean jets and passages.

6 Using the supplied spray nozzle extension on an aerosol can of carb/choke cleaner can extract dirt and debris.Caution:proper eye and skin protection is mandatory due to the fact this chemical (under pressure) can blow back into your eyes and/or onto exposed skin!

7 After installing a new float there will be instructions and data in your rebuild kit for resetting the float level and drop. This is critical to any carburetor.

8 If bowl plugs are removed for any reason, Teflon tape (or paste) can be used to seal the threads from fuel seepage.

9 This image shows a stiff wire can be inserted through a main jet for cleaning (via a removable bowl plug) and how it will exit through the venturi area.

10 With everything disassembled and laid out on a workbench, parts cleaning is next.

11 Any new leather accelerator pump should be soaked in gasoline prior to installation.

12 Age related grit and grime will work its way into every orifice of the carburetor.

13 Any good carburetor rebuild kit will supply necessary parts, exploded view of the carburetor, and technical data for adjustments.

Testing a Float

For brass floats, I use a combination of two different procedures. I hold the float close to my ear and shake it back and forth; if I hear a sloshing sound, it’s bad. I find a replacement. If I hear no sloshing sounds, I then hold the float with a pair of needle nose pliers (by the metal arm) and submerge it in a container of hot water. If the float is defective, air bubbles will rise to the surface. Again, I find a new replacement. Check the float/floats at the beginning. Don’t waste your money trying to repair a carburetor with a bad float. Also, certain floats can be next to impossible to find. No float available? Search for a rebuilt carburetor.

To test a fiber or plastic float — they must be weighed and compared to the weight of a new one. I use a postage meter for weight comparison. And, don’t let anyone tell you that a fiber float can’t soak up fuel and become overweight. As a rule of thumb, I replace all fiber floats for any carburetor rebuild where they’re used.

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