Parts of a Carburetor on a Small Engine

All 13 parts on the diagram

Show the list

In the air passage 3

Venturi The air has to speed up to pass it. This lowers its pressure there, and that is what draws fuel out of the main nozzle.
Choke valve Closed for a cold start, it lets in less air. The engine then gets a richer mixture.
Throttle valve It tilts with the throttle shaft. That lets more or less mixture into the engine, which sets the engine's speed and power.

Fuel parts in the bowl 5

Main nozzle Fuel rises through it. The air rushing past its tip carries the fuel off. Also called the discharge nozzle.
Main jet A precisely sized opening. All the fuel for the main nozzle passes through it, so its size helps set how much fuel the engine gets.
High-speed needle valve It meters the fuel on its way to the main nozzle. Turned in, the mixture at working speed is leaner. Turned out, richer.
Float It rises and falls with the fuel level. It works the float needle valve, so the bowl stays filled to the same level.
Float needle valve As the float rises it pushes the needle shut. That stops the fuel coming in. When the level drops, the needle opens again.

On the outside 5

Fuel inlet Fuel from the tank or the fuel pump enters the carburetor here. It goes to the float bowl.
Float bowl A small fuel store kept at a steady level for the nozzle. It comes off when the carburetor is serviced.
Idle mixture screw It sets the mixture while the engine idles. Too little air then passes the venturi for the main nozzle to work.
Throttle lever The engine's speed control and governor move it. It turns the throttle valve inside.
Idle speed screw It keeps the throttle valve from closing all the way. That sets how fast the engine idles.

How this list was compiled: Part names checked on 2026-09-30; a name is kept only when two independent sources use it. (1) US Army, TM 9-8000 Principles of Automotive Vehicles, 1985, chapter 4, https://archive.org/details/tm-9-8000-principles-of-automotive-vehicles-1985 (throat, venturi, discharge nozzle, float bowl, float, needle valve, fuel inlet, throttle valve and shaft, idle stop screw, main jet, choke valve, idle mixture screw). (2) Comprehensive Small Engine Repair, a vocational curriculum, 1977, unit on fuel systems, https://archive.org/details/ERIC_ED146392 (parts of a float carburetor: fuel inlet, float needle and seat, float, nozzle, needle valve, idle valve, throttle valve, venturi, choke valve; float bowl, main fuel nozzle, high speed needle valve, idle mixture screw). (3) A small engine maker's operating and maintenance instructions, https://archive.org/details/manualzilla-id-7348921 and https://archive.org/details/manualsbase-id-1525 (needle valve and high speed mixture valve, idle mixture valve, idle speed screw, carburetor throttle lever). (4) Wikipedia, Carburetor, text only (venturi, float chamber or bowl, needle valve, main jets, choke valve, throttle lever, idle mixture and idle speed adjusting screws). Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; no maker's carburetor, nothing traced. Licence: own work

How it works

A small engine's float carburetor mixes gasoline into the air on its way to the engine. The parts of a lawn mower carburetor and the parts of a snowblower carburetor are the same.

Read the full guide

Follow the air, then the fuel

In the cut view air enters at the left, passes the choke valve, speeds up through the venturi and leaves past the throttle valve. Fuel comes in at the fuel inlet, fills the float bowl until the float shuts the needle valve, and is drawn up the main nozzle into the venturi. The outside view has the parts you can reach: the bowl and the adjusting screws.

The float parts keep the fuel level steady; the jet and the screws set how much fuel meets the air.
This page names the parts and gives no settings. The engine's manual has those.

Questions and answers

What are the parts of a carburetor on a small engine?

In the air passage: the choke valve, the venturi and the throttle valve. For the fuel: the fuel inlet, the float bowl, the float and its needle valve, the main jet and the main nozzle. Outside: the throttle lever and two idle screws.

What does the float do in a carburetor?

It rides on the fuel in the float bowl. When the bowl is full the float pushes a needle valve shut, and when the level drops the needle opens and lets in more fuel. That keeps a steady level.

What does the choke do on a small engine?

The choke valve is a plate that closes off most of the air passage for a cold start. With less air the engine draws a richer mixture. It is opened again once the engine is running.

Are the parts of a snowblower carburetor different?

No. A snow blower, a lawn mower and a generator use the same kind of small float carburetor, with the same parts. The shape of the body and the place of the screws change from one maker to the next.