Back in the days of carbureted and plentiful used Plymouth Satellites, B-52's frontman Fred sang of the devil in his car. Beehive sporting singer Kate did Fred one better by wailing that she had the devil in her CAR-buretor! Having Beelzebub in the float bowl and demons clogging the jets is not a good thing at all. A carburetor rebuild can help exorcise evil spirits.
Hey, Bernoulli - Take it Easy!
The carburetor is one of those automobile parts of yesteryear still sworn by and at today. Like a modern electronic fuel injection system, the carburetor's main job is to meter fuel into the air entering the engine based on demand. Before modern multipoint electronic fuel injection became commonplace, the carburetor was the automotive king of mixing fuel and air. The carburetor mixes up fuel and air using Bernoulli's principle by way of a venturi. Bernoulli stated that air becomes less dense the faster it moves. As air moves through the throat of the carburetor, the vacuum created draws fuel into the air to in theory, produce the ideal fuel-air mixture based on engine demand. The carburetor venturi amplifies this effect by squeezing the incoming air into a tighter space, increasing velocity, and vacuum, and so on.
The carburetor mixes fuel into the air based on a near-ancient idea of a throttle cable connected to the loud pedal. The throttle plate meters air into the air pump that is the engine. If all goes well the carburetor sends the right amount of fuel to match demand. While multipoint fuel injection mixes the ideal amount of air and fuel together by way of various electronic sensors and a digital computer, the carburetor achieves this same task mechanically. The carburetor is a liquid analog computer. The carburetor uses a myriad of channels, passages, needles and seats, holes, check balls, and vacuum diaphragms instead of ones and zeros.
The devil is in the details. Anything with that many moving parts is bound to be a bit of a cantankerous device. The maze of snakelike vacuum tubes and sensors can paralyze even the initiated. Adding to the operating complexity of a carburetor is that it is bolted down to the top or the side of a perpetually shaking engine that goes from stone cold to two hundred plus degrees and back again all the time. Fuel leftover when the vehicle is turned off combined with engine heat conspires to gum up the works. Evaporating fuel leaves a legacy of varnish and glue.
Ships in a Bottle
Anyone who ever spent any time building models as a kid can rebuild a carburetor. Those of you who relish putting ships in a bottle, or that have a Apple 5300c connected to a car battery running the garage security system might even be able to wrestle a dreaded feedback carburetor back into useful service. The other trick is to get the right rebuild kit. The fusty old Aisin carburetor show here had almost a dozen kits available for the different versions Toyota bolted into the Starlet. Safety first! Gasoline is flammable. Always disconnect the battery and have an approved fire extinguisher nearby before beginning any work involving gasoline or other flammable fuels.
Stuff You'll Need:
· A Crusty Carburetor
· A Carburetor Rebuild Kit
· About Four Hours
· Hand Tools, Including Wicked Small Stuff
· Large Tray to Catch Check Balls and Clips
· Gunk®, Chem-Dip®, or similar
· Gloves and Goggles
Remove the air cleaner. Mark all hoses and connections for future reference because you won't remember. Replace any cracked or broken lines. Remove fuel line using a line wrench to prevent stripped nuts. Use a rag or metal cup to catch any fuel. Remove the carburetor and put a clean rag over the hole.
Move to the bench. Now is a great time to take a digital image of the carburetor for later reference. Break down only the parts that need to be taken apart. Try to keep linkages and levers whole if possible.
Lift off the top of the carburetor to reveal the accelerator pump, and float. Don't tip anything upside down, or a dozen different size ball bearings and check valves will fall out.
If the main jets need to be removed use a screwdriver that fills the screw slot. Any nicks or scratches in the jets can alter the flow of fuel.
The key to any successful carburetor rebuild is the dip. Bailing wire comes in handy for fishing out parts. Small parts go into included dipping basket. Don't leave aluminum in there too long.
The accelerator pump squirts fuel into the throttle bore when you hit the gas. Soak the leather in a little oil to soften it up before installing.
Set the float level and drop by bending tabs and measuring. Do it again, and again, and again until it's right. Float drop and level has great effect on carburetor operation.
This little bugger controls the idle fuel mixture. Make sure it's not worn out or mangled, and that the air passages feeding it are open. Turn the screw until it seats, then turn out according to the instructions.
New gaskets are the key to proper sealing. Set the throttle plate stop angle on the primary and secondary throttle blades. Some rebuild kits come with cardboard templates to make this easy. This kit did not. We had to bust out the protractor and make cardboard templates.
Put it all back together. Easy right? Don't forget to inspect fuel for rust and crud, and install a new fuel filter if required before bolting it back up. Tighten mounting bolts in a criss-cross pattern. Do not overtighten! The carburetor will warp.