The spring opens and closes the choke plate on top of the carburetor. Inside the choke housing is a coiled bi-metal heat-sensing spring that contracts when it cools and expand (unwinds) when it gets hot. Chokes are very sensitive, and easily misadjusted (which is why the government required the auto makers to make choke and idle mixture adjustments 'tamper-resistant' in the 1980s). But there's no need to rebuild or replace the carburetor if all that's needed is a simple adjustment or cleaning of the choke mechanism and linkage. Hard starting can be caused by a choke that fails to close and causes a rich fuel mixture when the engine is cold. Carburetors can be tricky to rebuilt, and expensive to replace, so you want to be sure of your diagnosis before you touch this critical part.Ī choke is necessary for cold starting to richen the Air/Fuel mixture and increase idle speed while the engine is warming up. Sometimes it is the carburetor and sometimes it is something else. Problems that are often blamed on a 'bad' or 'dirty' carburetor include hard starting, hesitation, stalling, rough idle, flooding, idling too fast and poor fuel economy. The engine should get normal fuel economy and emissions should be within limits for the year of the vehicle.

When a carburetor is clean and is working properly, the engine should start easily (hot or cold), idle smoothly, and accelerate without stumbling.

By the mid-1980s, carburetors were history on new production vehicles, having been replaced by throttle body and multiport electronic fuel injection systems. Changes in emission regulations in the early 1980s made carburetors obsolete because they were unable to meet the new emission requirements. Though the basic operation of a carburetor is fairly simple, it also relies on a number of add-on devices for cold starting, idle control and emissions. The air/fuel mixture then flows down through the intake manifold and into the cylinders where it is burned to produce power. At higher engine speeds, fuel is pulled through the main metering jets into the venturi (the narrowest part of the carburetor throat). At idle, the fuel enters the carburetor throat through one or small small idle ports just above the throttle plate. As air is pulled down through the throat of the carburetor by intake vacuum, fuel is siphoned from the carburetor's fuel bowl and mixed with the incoming air to form a combustible mixture.

How to Diagnose and Repair Carburetor Problems by Larry Carley copyright Ī carburetor uses intake vacuum to supply fuel to the engine. How to Diagnose & Repair Carburetor ProblemĪuto Repair Library, Auto Parts, Accessories, Tools, Manuals & Books, Car BLOG, Links, Index

Carburetor troubleshooting guide