How to Adjust a Tecumseh Carburetor

Adjusting the carburetor on your Tecumseh engine is a great way to maximize its performance. Properly tuning your carburetor will help your engine start easier, run smoother, and perform better. This comprehensive guide will walk you through the entire process of adjusting a Tecumseh carburetor.

Understanding Carburetor Basics

Before diving into the steps for adjustment, it helps to understand what a carburetor does and how it works.

  • A carburetor is the part of an engine that mixes air and fuel for combustion. It is a crucial component that directly impacts engine performance.
  • Carburetors regulate the ratio of air to fuel via different circuits and jets. Proper air/fuel mixture is critical for smooth engine operation.
  • Most Tecumseh carburetors are float-type carburetors. This means they use a float and needle valve assembly to regulate fuel delivery based on air flow.
  • Key carburetor circuits include:
    • Main jet circuit – Provides fuel for mid to high RPM range
    • Low speed circuit – Controls fuel at idle and low speeds
    • Choke circuit – Enriches fuel mixture for cold starts
  • Adjusting the carburetor involves tuning the air and fuel flow through these circuits to optimize performance.

Gather Necessary Tools

Adjusting the carburetor requires some specific tools. Having these tools on hand will make the job much easier:

  • Screwdrivers – Both flathead and Philips head screwdrivers in various sizes
  • Wrenches – Including adjustable wrenches and wrenches for the jets
  • Clean rags – For cleaning parts during disassembly
  • Carburetor cleaner – For spraying down components
  • Compressed air – For blowing out passages
  • Feeler gauges – For setting gaps and clearances
  • Tachometer – For checking RPM during adjustment
  • Shop manual – Contains specifications and steps

Prepare the Engine

Before starting the adjustment process, the engine should be prepped properly:

  • Make sure the engine is cool before working on the carburetor. Hot components can cause burns.
  • Disconnect the spark plug wire to prevent accidental starting.
  • Clean the exterior of the carburetor with a degreaser and brush. Removing dirt and debris will allow for smooth disassembly.
  • Have a container ready to hold bolts and small components. This will prevent losing any pieces.
  • Review the shop manual and become familiar with each step before beginning.

Disassemble the Carburetor

With the tools gathered and engine prepped, you can now start disassembling the carburetor:

  1. Remove air filter assembly and air intake hose. This allows access to the carburetor.
  2. Take out fuel line from fuel inlet fitting. Have a rag ready to catch any drips.
  3. Detach throttle cable from throttle lever. Make note of routing for reassembly.
  4. Remove carburetor mounting nuts and carefully separate carburetor from engine.
  5. Take out idle mixture screw and slow speed jet. Note position of screw for reinstallation.
  6. Remove bowl nut and detach float bowl from carburetor body. Watch for bowl gasket.
  7. Take out float pin and lift out float. Be gentle to avoid bending or breaking.
  8. Remove main jet from carburetor body using a jet wrench.
  9. Carefully take out nozzle tubes and power jet using screwdriver. Note orientation.
  10. Spray all components with carburetor cleaner. Blow out passages with compressed air.

Inspect Components

With the carburetor disassembled, closely inspect each component:

  • Float – Check for cracks, holes, and missing plastic at tip. Check that float is not filled with fuel.
  • Needle – Examine needle tip for wear and look for any binding in the seat.
  • Jets – Ensure openings are clear of debris and obstructions. Orifices should be round.
  • Gaskets – Replace any gaskets that are hard, brittle, or damaged. Reusing old gaskets can cause leaks.
  • Body – Check for cracks and make sure all holes are open.
  • Throttle lever – Confirm lever and shaft move smoothly without binding.

Replace any components that are worn or damaged. This will ensure proper carburetor operation after reassembly.

Adjust Float Level

One key adjustment is setting the proper float level:

  • Hold the carburetor body upside down and measure from the bowl mating surface to the top of the float.
  • Consult the shop manual for the specified float level for your carburetor. Often it is between .62-.75 inches.
  • To adjust, gently bend the float tab as needed to achieve the proper float height.
  • Check the measurement again. Make small adjustments until within specification.

Proper float level is critical for consistent fuel flow and preventing flooding.

Adjust Low Speed Circuit

The low speed circuit controls the air/fuel mixture at idle and low RPMs. To tune this circuit:

  1. Turn idle mixture screw clockwise until lightly seated. Never force.
  2. Back screw out counterclockwise to the specified opening, usually around 1.5 turns out.
  3. Start engine and allow to warm up. Listen for smooth idle without sputtering.
  4. Adjust screw in 1/8 turn increments to achieve highest, steady idle speed.
  5. Readjust screw to maximize throttle response without stalling when rapidly cycling throttle.
  6. Recheck idle speed and adjust screw as needed for optimal low speed operation.

Adjusting the low speed circuit prevents stalling and allows the engine to transition smoothly off idle.

Adjust Main Jet Size

The main jet controls fuel delivery in the mid to high RPM range:

  • Install the recommended main jet size indicated in the shop manual as a starting point.
  • Start engine and run through full throttle range, noting power output and performance.
  • If engine is running lean (misfiring or surging), increase main jet size to richen mixture.
  • If engine is running rich (black smoke or poor acceleration), decrease main jet size to lean mixture.
  • Make adjustments in small increments until engine runs cleanly with optimal power.

Selecting the proper main jet size will provide strong performance across the engine’s RPM range.

Reassemble Carburetor

With the adjustments complete, reassemble the carburetor:

  1. Install main jet, nozzle tubes, and power jet in proper orientations.
  2. Attach float and inlet needle onto float pin. Verify float moves freely.
  3. Position float bowl gasket and tighten bowl nut to carburetor body. Torque to specifications.
  4. Insert idle mixture screw into carburetor body and turn in lightly until seated.
  5. Attach fuel line to inlet fitting. Use new clamp if original is damaged.
  6. Connect throttle cable to throttle lever and check full range of motion.
  7. Mount carburetor to engine using new gasket. Tighten nuts evenly.
  8. Reconnect air intake components and spark plug wire.
  9. Start engine and test for smooth operation, proper idle speed, and throttle response.
  10. Make final adjustments if needed. Be methodical and make changes one at a time.

Proper reassembly and double checking your work helps ensure optimum carburetor function.

Troubleshooting Common Carburetor Issues

If the engine still is not running correctly after carburetor adjustment, some common issues to check include:

Engine stalls or is hard to start:

  • Float level too high – Not enough fuel delivery
  • Clogged idle jet – Insufficient fuel at low speeds
  • Low speed screw closed too far – Air/fuel mixture too lean

Rough idle:

  • Float level too low – Too much fuel flooding engine
  • Idle speed set too low – Engine RPM dipping
  • Vacuum leak – Extra air entering system

Hesitation or lack of power:

  • Clogged main jet – Not enough fuel in mid-high RPMs
  • Main jet too small – Mixture too lean when accelerating
  • Sticky throttle linkage – Throttle not opening fully

Black smoke from exhaust:

  • Float level too high – Overfilling engine with fuel
  • Main jet too large – Too much fuel in combustion chamber
  • Air filter dirty – Less air entering carburetor

Carefully inspecting symptoms and causes can reveal issues during troubleshooting.

Best Practices for Smooth Operation

Follow these tips for keeping your Tecumseh carburetor in top running condition:

  • Replace the fuel filter annually to prevent contamination in the carburetor.
  • Clean the air filter regularly to allow proper airflow into the engine.
  • Use fresh, clean gas and fuel stabilizer to prevent deposits in the carburetor.
  • Periodically check for vacuum leaks which can impact air/fuel ratios.
  • Adjust valve lash clearance per manufacturer specifications for smooth running.
  • Check float level and perform tune-ups at the start of each season.
  • Keep carburetor stored in a sealed container during the off-season to prevent corrosion.

Proper maintenance and storage extends the life of your carburetor and engine.


Adjusting a Tecumseh carburetor involves carefully disassembling, cleaning, inspecting, tuning, and reassembling the component. Paying close attention to details such as float level, proper jet sizes, and air/fuel screw settings allows you to dial-in performance. Following the steps outlined in this guide will help you successfully adjust your Tecumseh carburetor. Be patient, methodical, and make changes one at a time until the engine runs smoothly. Proper carburetor adjustment results in easier starting, smoother idle, and maximum power across the RPM range.

Key Takeaways:

  • Gather all necessary tools before disassembling the carburetor
  • Thoroughly clean individual components and blow out all passages
  • Adjust float level first, then fine tune low speed and main jet circuits
  • Make adjustments in small increments and test performance
  • Be systematic when troubleshooting issues using engine symptoms
  • Follow best practices like regular maintenance for optimal operation

Citations: [1] [2] [3] [4] [5] [6]

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