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4x4 Carburetor Maintenance & Repair Basics

Posted in How To: Engine on April 1, 2008
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Now That We're Paying more than $3 for a gallon of gas with no relief is in sight, it's important that we pay attention to the proper maintenance, care, and tuning of all our vehicles, even our toys. Listening to the experts speculate about the steady rise in demand for fuel makes just about all of us middle-class folks cringe, especially when they keep telling us these soaring prices are going to keep climbing.

In this day and age of simpler fuel-injection conversions, believe it or not, carburetors can be the right application and fuel-delivery system for your off-highway performance needs. This is especially true if you are on a budget and can't afford that super-expensive, wazoo efi kit. The repair of an old carb may run just under $50, a new carb may cost a little over $600, while a fuel-injection system will run you $1,000 and up. A properly maintained and tuned carburetor can deliver all the performance you may ever need. This is especially true with the new generation of off-road carburetors, which can perform at angles up to 40 degrees of incline. They may not work as well upside down like fuel injection, but you're supposed to keep your vehicle wheel-side down anyway.

If you have a carb that is running poorly or is hard to start, there could be some minor problems easily solved with just an hour or two of work. You can find just about any carburetor's rebuild kit at the corner auto parts store. Tech tips and installation manuals are easily found on the manufacturers' Web sites.

We found this tired and poorly running Holley Truck Avenger carb on an early Ford Bronco at West Coast Broncos in yucca valley, California. These guys know their carburetors, and old Bronco enthusiasts seem to love them. This Bronco was running rough, didn't have a steady idle, and was hard to start. This makes it difficult to wheel in critical off-road situations when smooth acceleration and steady idle are necessary. Numerous things could be wrong with a carb like this, but one of the first and easiest tests you can complete on this carburetor is a check for leaks. Simply take a can of brake cleaner and spray around the carb. If you hear a change in the engine's idle speed, then you have a leak. We found the gasket between the metering plate and the front float bowl was leaking.

Removal of the carb is almost as easy as checking for leaks. If you are unsure of your memory, label each part and connection point with a numbered piece of tape, and list where it goes on a note pad. You can also snap a few photos of the carb before you disassemble it. Carefully remove the air cleaner, throttle linkage, vacuum hose, fuel line, and choke wires. If your carburetor has two vacuum lines, remember where they go. One is for the distributor-timed vacuum, and the other is for the manifold vacuum line.

1. Primary Float Bowl
2. Float
3. Float Spring Primary
4. Metering Plate
5. Power Valve
6. Jets
7. Pump
8. Pump Diaphragm

The Holley Avenger carburetor has two float bowls; only the primary (front) has a metering plate. Double-pumper carb would have two metering plates. The metering plate on the Holley is where you would change your jets if needed. Notice the spring (3) under the float; this keeps the float from moving around while your vehicle is at extreme angles and keeps the carburetor from flooding.

Here is the side of the carb body we cleaned. Since the float bowl and metering plate are off, now's a good time to inspect the power valve, float, spring, jets, and pump diaphragm. The Holley rebuild kit comes with just about everything you need to rebuild the carb except the float. Sometimes it's hard to tell if these little parts are bad, so if you have the kit, just replace them. We replaced the power valve, the float needle, and the seat, and always highly recommend changing the pump diaphragm even if the old one looks good.

Once the carb is off the manifold, look for anything out of the ordinary. If it's dirty and gummed up, it may be necessary to completely disassemble it and carefully clean it. This Holley carb wasn't that dirty so we just stuck with the gasket repair in the primary float bowl. When you are cleaning the old gasket off any surface, take great care not to gouge the metal. You can dry the carb and blow out any old material with your air hose. Hold the air nozzle laterally to any part so you don't blow any old material into the ports and passages. There are chemical gasket strippers available but inevitably you always end up manually scraping off some of the old gasket. Using a plastic scraper is also a safe way to make sure you don't damage any parts.

PhotosView Slideshow

With the new gaskets and metering plate in place, the bowl is ready to screw on. After that you can reinstall the accelerator pump. Be careful not to overtighten the screws or you will spend more time trying to tap the screw holes.

Make sure you clean the intake manifold thoroughly and install a new gasket. While the carb is removed, it's a good idea to stuff the intake ports of the manifold with clean rags. This will keep any nuts, bolts, and old gasket material from dropping in. If something falls in, you just added hours to your minor carb repair. Installation of the carb is just the reverse of its removal: easy. Just be sure not to overtighten anything.

Upon reassembly you can use an old hot-rod trick and very lightly coat the gasket with Chapstick. This keeps the gasket from sticking if you need to remove it again, especially if you are a tinkerer and keep playing with the jets.

Adjustment of the accelerator pump is critical and needs to be exact. There are many theories on the adjustment, but we feel that it should have some play so the lever won't be bent. The arm should move when the accelerator pump cam moves but should not be too tight.

This is a common carburetor repair we completed. But what we are really telling you here is don't be afraid to get your hands dirty and work on your own junk. As with all things mechanical, there are literally hundreds of things that can go wrong and thousands of fine-tuning adjustments that you can make.

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