Stop being afraid of your carburetor
To many automotive enthusiasts, the carburetor exists on a level somewhere between mystery and magic—but I’m here to tell you that it’s not so scary to rebuild one. If you like working puzzles or building model kits, you already have the skills you need.
Let’s start by looking at my 1966 Sunbeam Tiger. It’s completely stock, with a 260-cubic-inch Ford V-8 under the bonnet. Although Rootes Group, the parent company of Sunbeam, sourced the motors through Ford’s Industrial Division back in the ’60s, there’s nothing particularly industrial about it; this is the same engine found in thousands of Fairlanes, Galaxies, and even ’64½ Mustangs. The carburetor is an Autolite 2100 two-barrel, as found on various Fords for something like a million years, and I’m going to walk you through a pretty simple rebuild process. It’s the original carburetor for my car, so I’d certainly like to rebuild it instead of replacing it if possible.
Here’s the problem: The Tiger had been running well for a while, but it suddenly developed a rough idle and a step-off bog so bad the car would die when I tried to leave from a stoplight. Not good.Slipping the clutch long enough to get the revs up would do the trick, after which the engine would just stumble along at cruise.
I had noticed some dripping around the accelerator pump gasket, and it was also wet underneath the carburetor. I suspected the gaskets around the base of the carburetor had perished. There’s an old trick of spraying carburetor cleaner around them to check for vacuum leaks. Sure enough ,when I sprayed the base of the rear of the carb, the RPM would change. With what looked like plenty of potential problems, I figured I’d just go through the carb and replace everything.
First stop was my local parts store, which had a rebuild kit in stock for the stunningly low price of $17. As usual, I had to tell the parts guy it was for a 1964 Fairlane. I’ve yet to find a parts store that has a proper look-up for a Sunbeam Tiger. No matter, let’s get to it.
In addition to removing the carburetor, I wanted to replace the gaskets both above and below the carburetor spacer. On my car, it actually runs hot water through it to help warm the intake air and keep the mixture vaporized nicely. Lots of people disable this, but since my engine is stock, I’m leaving it as the factory designed it. So I had to disconnect the fuel inlet, a water inlet and outlet, a metal vacuum line to the advance on the distributor, a large vacuum line to the PCV valve, and a throttle connection. Literally five minutes later, the carb was on the bench.
Another thing I noticed was that even though the carburetor was stone cold, the choke plate was stuck in the wide-open hot running position. Looks like I had something else to investigate.
The supplies I needed (in addition to the carb kit) included a flat head screwdriver, a razor blade to clean the gasket surfaces, and a couple of simple open wrenches. I also used a little sandpaper around the water inlet and outlet openings on the spacer plate.
Don’t get hung up about the function of each gasket or little shiny part; just carefully remove and replace. On the outside of the carburetor you will find the accelerator pump and power valve assembly at the front and underside of the carburetor. On the inside are the various jets, tubes, and the float assembly. It really is just as simple as removing the screws, carefully setting aside each little assembly, and matching up the little parts inside with what you see in the kit. Just make sure that whatever parts come out get put back in.
When you remove the top of the carburetor, don’t forget the long bolt that goes through the center. You may think it’s just there to give the air cleaner somewhere to attach. Nope, it’s the last bolt for the carburetor top, and it’s got to go. Once out, just jiggle it up and off the little air horn choke plate arm, and you’ve got a great view of the rest.
I was happy to see that my carburetor still had a brass float in it. A little test of filling the bowl with fuel told me it was still in good condition. It’s held in by a little snap wire, just pry it off carefully and then it all comes out, giving you access to the needle and seat assembly. Again, just match up the parts that come out with what you have in your kit—match and replace. This is also a good time to check out the bowl to see if there’s a bunch of grit inside. Mine looked pretty good, just a little residue but nothing too serious.
Again, a few simple wrenches and screwdrivers gets all this apart. There really isn’t anything too complicated about any of this. Everywhere you see a little hole, fill it with carb cleaner using the little red straw that comes with the can, which really helps direct the stream and gives it some force to scour the orifices clean. This is just a mixing box for fuel and air, and there are lots of passages for both. I cleaned them all very thoroughly, as my suspicion was that the idle circuits were clogged up from fuel residue or dirt that had made it by the filter over time. Underneath each brass item is normally a little gasket, so make sure you are getting that out of there to replace from your kit.
An interesting note about this part: See those two little brass items down at the bottom of the fuel bowl? Those are the main jets, and inside those are little holes that meter the amount of fuel in a particular ratio with the air. When people talk about changing the jets on the carburetor, this is what they are actually changing. You simply unscrew them with a large flat screwdriver. I discovered something interesting about mine, once I got them out and inspected them. They were marked 42F, which is a pretty small jet for sea level. The car was sold originally in Wyoming, then passed through owners in Colorado and New Mexico before I bought it in 2012. I’m guessing this thing has always been tuned for 5000 feet of altitude, so I’m going to investigate a change there. It’s not hurting anything as is, but it probably won’t hurt anything to richen the mixture up a touch.
Working my way through the carburetor, I unscrewed the plastic cover on the hot air choke and removed the spring inside. Some carburetors are completely manual, others may have electric wires here to control the actuation of the plate. This hot air choke simply pulls air from a hollow tube that goes through the exhaust manifold, and the hotter the air the more the plate opens. Well, it does if it’s working right! The little piston connected to the spring was bound up in the bore, but after some WD-40 and some moving around, I got it to work smoothly again.
I was just about out of parts and gaskets at this point, so it was time to put it all back on the car. Again, a pretty easy process of reversing what I had carefully done an hour or so earlier. I cleaned the mating surfaces carefully with both chemicals and the blade, and settled it all down on the manifold. I hooked up the water, fuel, and throttle, and double checked the connections.
It’s a good idea to reset the idle adjustment screws as well, simply turn them in (righty tighty) until they bottom out gently, and then back them out exactly one and a half turns each. This generally gets you back to a baseline idle setting. You should have taken them out all the way to clean the passages with carburetor cleaner, so this gets them back in properly. This is also a good time to replace your fuel filter.
Once that’s done, we are buttoned up and ready to test! The fuel bowl will be bone dry, so you can expect to crank it for a minute before the fuel gets back to a useful level in the bowl. If you don’t want to wait, add fuel to it before you place it on the car. You can also fill it with a small funnel through the vent tube. I get to cheat a little here, because Tigers have an electric fuel pump.
I just turned the key one click to the right, and I could hear the pump moving fuel from the rear of the car into the carburetor. When everything quieted down, I knew it was ready. It fired right up and settled into a nice, smooth idle right away, just like old times! The choke plate was back to the proper cold setting, I wasn’t getting any leaks around the base gaskets, and it had a nice proper rush through the RPM’s instead of a hesitation. The test drive was also a success—I had a proper Tiger again, which is pretty good considering I’m about to put about 2500 miles on it when I head to the Amelia Island Concours next month.