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Know-How Notes: How To Perform A Simple Carburetor Refresh

Know-How Notes: How To Perform A Simple Carburetor Refresh

So you finally got around to working on that old project car you had sitting outside, eh? It happens to the best of us, you lose track of time and a car sits for way too long between drives. If you let it sit too long, your carb can get pretty gunky and may require servicing before it will actually run. Gas slowly evaporates in the fuel bowl, and this process leaves a lot of varnish on the metal. The main issue here is that the needle and seat can become frozen in place. When that happens, you will either get too much fuel in the bowl or no fuel at all. A carburetor refresh can solve these issues.

When good carbs go badA young woman working on a carburetor

In most cases you will need to do a carburetor refresh in order to make it function. While you might be able to get a sticky needle and seat to regain function, it is best to replace it as you will eventually have the same issue later one. Another issue that can wreak havoc on your enjoyment of an older car is leaky carb gaskets. Over time, as little as a year of non-use, the gaskets may shrink, causing fuel and air leaks that render the carburetor less than efficient. If you are anything, like me, you probably HATE tuning a carb. It is my Achilles heel, and I am just not good at it. You might find yourself putting off a rebuild simply because getting it tuned will be a chore. There are options though, and as you will see here, you can refresh the internals of a carb without having to re-tune it. *(AUTHOR NOTE: You will eventually need to make adjustments, but this method will get your engine running and it will be very close to the previous tune). With the help of my daughter (this is her car), we had the VW Bug up and running in a single afternoon.

Getting started

We recently resumed work on a 1974 VW Beetle that has a performance-built 1836cc engine with twin Kadron carbs. We had the car running a few years ago, but it had sat for eight years, so the carbs needed serious work. We managed to get the needle and seats to operate, but they would stick regularly, so the car ended up sitting for a couple more years. A carburetor refresh was necessary, and we picked up the parts from our local NAPA Auto Parts Store. With the carb kits in hand, we sat down and got to work on our carburetor refresh. There are several key points to this project if you want to save yourself some hassle. When removing the carb(s), simply disconnect the linkages and set aside. Do not adjust them or change anything. If you have to unthread a linkage, mark the position with tape so you can get right back to where it was before removal. 

When a carb sits too long, corrosion can cause the internals to stick like the throttle blades on this carb.
When a carb sits too long, corrosion can cause the internals to stick like the throttle blades on this carb.

 

The model numbers are usually on the side of the carb, like this one.
The model numbers are usually on the side of the carb, like this one.

We pulled the carbs off the engine, leaving all of the adjustments as they were. These small carbs are simple and easy to work on without changing all of the settings, but some carbs require everything be removed when rebuilding. If that is the case, you can use paint or a scratch awl to mark the positions of the idle air mixture and idle speed screws. 

This screw is for adjusting the idle air/fuel mixture. We are leaving this alone.
This screw is for adjusting the idle air/fuel mixture. We are leaving this alone.

You will need a few tools and supplies to perform this refresh. We used Berryman Chem-Dip carb cleaner dip, which is very efficient and even comes with a parts basket in the can. This is 1-gallon and can be reused. You will also need a few hand tools like screwdrivers, sockets and wrench, and a pick. We started by removing the bolts that hold the top half of the carb to the main body. A slight tap with a wood handle or screwdriver is usually all you need to break the seal on the gasket. 

Four bolts held the top of the carb on, we removed them and tapped the body with a wood handle and the top came right off.
Four bolts held the top of the carb on, we removed them and tapped the body with a wood handle and the top came right off.

The paper gaskets had shrunk considerably since these carbs were last rebuilt, about 11 years ago. The new carb kit has all the gaskets you need. 

This carb is only 10 years old, but the gaskets are quite shrunk, which would have leaked even if the guts of the carb were functional.
This carb is only 10 years old, but the gaskets are quite shrunk, which would have leaked even if the guts of the carb were functional.

One this carb, the needle and seat are bolted to the top of the carb, on others it may be in the main body. This can be removed now. 

The needle and seat is a single threaded unit, which we will replace.
The needle and seat is a single threaded unit, which we will replace.

On the main body, the fuel float is secured with a little plastic “bone”, which keeps the float from rising in its mount instead of rotating on the hinge pin. The float lifts right out. You will want to check the float for signs of holes or damage. The float should float in a glass of water. If it rattles when you shake it, it is probably bad. To test a float, submerge it in a glass of water. If you see bubbles rising, then it has a pinhole leak and needs to be replaced. 

Most fuel floats are held in with a small piece of plastic like this to ensure smooth operation.
Most fuel floats are held in with a small piece of plastic like this to ensure smooth operation.

One of our carbs was badly corroded at the butterfly. We used some Mac’s Carb Cleaner to breakdown the corrosion and get the butterfly moving again. 

We showed the corrosion previously, which we treated with some carb cleaner to break it up.
We showed the corrosion previously, which we treated with some carb cleaner to break it up.

On the underside of the main body resides the diaphragm, this is the part that pushes out fuel when you first hit the throttle. The pump cover is removed and the small diaphragm and spring can be taken out. 

Under this cap is the pump diaphragm, which will be replaced as well.
Under this cap is the pump diaphragm, which will be replaced as well.

 

This is the diaphragm and spring, the diaphragm gets replaced, but the spring is retained.
This is the diaphragm and spring, the diaphragm gets replaced, but the spring is retained.

This is the extent of the disassembly we are taking on. You can remove the adjustment screws, but in this case, it just isn’t necessary. We placed all of the components into the carb dip and let it set for 20 minutes. 

The body of the carb was placed into the dip and left to soak for about 20 minutes.
The body of the carb was placed into the dip and left to soak for about 20 minutes.

After the allotted time, we removed the parts and washed them off with a garden hose. The varnish inside and outside the carb is all gone, nice and clean. 

After 20 minutes, we washed off the parts with a water hose.
After 20 minutes, we washed off the parts with a water hose.

Reassembly

At this point, we began the assembly process. It goes in reverse order of the disassembly. 

Now that the parts are cleaned, we can start the assembly process. You can see just how clean the throttle blade is, this was black and crusty only half an hour ago.
Now that the parts are cleaned, we can start the assembly process.

 

The gaskets are sometimes directional, as is this one. Be careful to make sure the holes line up, this can be critical to the function of the carb.
The gaskets are sometimes directional, as is this one. Be careful to make sure the holes line up, this can be critical to the function of the carb.

 

There are two hidden screws that hold the throttle base plate to the main body.
There are two hidden screws that hold the throttle base plate to the main body.

 

Then we installed the pump diaphragm. This piece is under pressure, so take care that the diaphragm doesn't get pinched when you assemble it.
Then we installed the pump diaphragm. This piece is under pressure, so take care that the diaphragm doesn’t get pinched when you assemble it.

 

The main body gasket is die-cut to clear the internals, this must be assembled correctly.
The main body gasket is die-cut to clear the internals, this must be assembled correctly.

 

The finished carb is ready to go back on the car. We were able to carburetor refresh it without changing any of the settings, it fired up and ran well.
The finished carb is ready to go back on the car. We were able to refresh it without changing any of the settings, it fired up and ran well.

The entire carburetor refresh project took us about two hours for each carb. We didn’t change any of the settings, so we don’t have to tweak anything in order to get the engine to run. Once the carbs were reinstalled onto the engine and primed via the engine’s fuel pump, it still would not run. We swapped out all the spark plugs, and it fired right up and ran like a dream. No missing, no choking out, and it accelerates very well. Before we refreshed the carbs, you couldn’t even get them to take fuel from the pump. 

Check out all the fuel & emission system parts available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on how to perform a carburetor refresh, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Jefferson Bryant View All

A life-long gearhead, Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 4 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.

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