How to Clean a Carburetor | Small Engine Guide

Repair Guides
T
Tom Bradley
Certified Small Engine Mechanic, 25+ Years Experience
Carburetor being cleaned and serviced
Carburetor being cleaned and serviced

A dirty carburetor causes more small engine problems than any other single component. Old fuel leaves varnish deposits that clog the tiny passages responsible for precise fuel metering. The good news: cleaning a carburetor is straightforward with the right approach and saves the cost of replacement.

Table of Contents

When to Clean vs Replace

Cleaning works for most carburetor problems. Replacement becomes necessary when physical damage exists.

Carburetor ready for cleaning Most carburetor issues respond well to thorough cleaning

Clean When:

  • Engine won’t start after storage
  • Engine runs rough or surges
  • Engine dies at idle
  • Engine lacks power under load
  • Visible varnish deposits

Replace When:

  • Throttle shaft worn (causes air leaks)
  • Body warped or cracked
  • Threads stripped
  • Cleaning attempts have failed repeatedly
  • Cost difference is minimal

Basic carburetors cost $15-40; cleaning takes about an hour. Complex carburetors cost more, making cleaning more worthwhile.

Tools and Supplies Needed

Gather everything before starting:

Essential Tools

  • Socket set and wrenches
  • Screwdrivers (flathead and Phillips)
  • Needle-nose pliers
  • Small wire brush
  • Compressed air
  • Clean work surface

Cleaning Supplies

  • Carburetor cleaner spray
  • Carburetor dip (for soaking)
  • Small cleaning wires or bristles
  • Clean rags
  • Parts tray or containers
  • Carburetor rebuild kit (gaskets, needle, seat)
  • Digital camera or phone for photos
  • Service manual for your engine
  • Safety glasses
  • Nitrile gloves

Carburetor Removal

Proper removal prevents damage and ensures clean reinstallation.

Preparation

  1. Disconnect spark plug wire for safety
  2. Drain fuel or close fuel shutoff
  3. Take photos of linkage connections
  4. Note adjustment screw positions (count turns from seated)

Removal Steps

  1. Remove air filter and housing
  2. Disconnect throttle linkage
  3. Disconnect choke linkage (if separate)
  4. Disconnect fuel line
  5. Remove mounting bolts or nuts
  6. Carefully remove carburetor
  7. Remove gasket (note orientation)

Common Mistakes to Avoid

  • Forcing stuck linkages
  • Losing small springs or clips
  • Forgetting to close fuel supply
  • Not documenting connections

Carburetor removal process Document linkage positions before removal

Disassembly and Cleaning

Systematic disassembly ensures nothing gets lost or damaged.

External Cleaning

Before disassembly, clean the exterior:

  1. Spray exterior with carburetor cleaner
  2. Brush away loose debris
  3. Wipe clean with rag
  4. This prevents contaminating internal parts

Bowl Removal

  1. Remove bowl retaining bolt or screws
  2. Carefully lower bowl straight down
  3. Note float position and orientation
  4. Remove float pin
  5. Remove float and needle

Jet Removal

  1. Locate main jet (usually in center post)
  2. Remove with proper-fitting screwdriver
  3. Remove any additional jets (idle jet, emulsion tube)
  4. Note positions and orientations
  5. Store jets safely—they’re tiny and easily lost

Cleaning Process

Spray cleaning:

  1. Spray all passages liberally with carburetor cleaner
  2. Allow to soak 5-10 minutes
  3. Blow through all passages with compressed air
  4. Repeat until passages flow freely

Soak cleaning (for heavy deposits):

  1. Place metal parts in carburetor dip
  2. Soak according to product directions (usually 30 minutes to overnight)
  3. Remove and rinse
  4. Blow dry with compressed air

Jet cleaning:

  1. Spray through jet holes
  2. Use fine wire to clear if blocked
  3. Never drill or enlarge jet holes
  4. Hold to light to verify clear passage

Critical Passages

Focus on these commonly clogged areas:

  • Main jet: Primary fuel metering
  • Pilot/idle jet: Low-speed operation
  • Emulsion tube: Fuel/air mixing
  • Idle circuit passages: Tiny holes in throttle bore
  • Fuel inlet: Where fuel enters from tank

Reassembly and Installation

Reverse the disassembly process with attention to details.

Reassembly Order

  1. Install main jet (don’t overtighten)
  2. Install emulsion tube if separate
  3. Install needle and seat
  4. Install float with pin
  5. Verify float height (if adjustable)
  6. Install new bowl gasket
  7. Attach bowl

Float Height Check

Float height affects fuel level in the bowl. Improper height causes:

  • Too high: Flooding, rich running
  • Too low: Fuel starvation, lean running

Check against specifications. Adjust by bending float tang carefully.

Gasket Notes

  • Use new gaskets from rebuild kit when possible
  • Old gaskets may seal if undamaged
  • Apply thin coat of oil to gaskets
  • Don’t use sealant on carburetor gaskets

Carburetor reassembly Careful reassembly ensures proper function

Installation

  1. Position new intake gasket
  2. Mount carburetor to engine
  3. Tighten mounting hardware evenly
  4. Connect fuel line
  5. Reconnect choke linkage
  6. Reconnect throttle linkage
  7. Verify full throttle and choke travel
  8. Install air filter housing

Adjustment and Testing

Proper adjustment ensures optimal performance.

Initial Settings

Return adjustment screws to noted positions or manufacturer specifications:

  • Idle mixture screw: Usually 1 to 1.5 turns out from seated
  • Main mixture screw (if present): Usually 1 to 1.5 turns out
  • Idle speed screw: Set for specified RPM

Starting Procedure

  1. Reconnect spark plug wire
  2. Turn on fuel supply
  3. Prime if equipped with primer bulb
  4. Set choke for cold start
  5. Start engine
  6. Allow brief warm-up

Fine Tuning

Idle mixture adjustment:

  1. Engine at operating temperature
  2. Turn idle mixture screw slowly in until engine stumbles
  3. Turn out slowly until engine smooths and speeds up
  4. Continue turning out until engine starts to stumble
  5. Return to midpoint of smooth operation

Idle speed adjustment:

  1. Set to manufacturer specification (usually 1,400-1,800 RPM for mowers)
  2. Adjust idle speed screw until correct
  3. Re-verify mixture after speed adjustment

Performance Testing

  • Verify clean idle
  • Check throttle response
  • Test under load
  • Verify no fuel leaks
  • Check for steady operation at all speeds

Preventive Measures

Prevent future carburetor problems:

Fuel Stabilizer

Add stabilizer to fuel, especially for seasonal storage. Stabilized fuel resists varnish formation for up to 12 months.

Fuel Shutoff

Before storage, run engine until it dies from fuel starvation (with fuel valve closed). This empties the carburetor bowl.

Quality Fuel

Use fresh fuel from high-turnover stations. Avoid ethanol blends over 10% for small engines when possible.

Regular Use

Engines that run regularly develop fewer carburetor problems than those sitting for months.

Frequently Asked Questions

How do I know if my carburetor needs cleaning?

Symptoms include hard starting, rough running, surging, stalling at idle, black smoke, or poor performance. These often appear after storage with fuel left in the carburetor.

Can I clean a carburetor without removing it?

You can spray cleaner into the intake and through accessible ports, which helps minor cases. Thorough cleaning requires removal and disassembly.

How long does carburetor cleaning take?

Plan about 1-2 hours including removal, cleaning and reinstallation. Heavily varnished carburetors requiring soaking take longer.

What’s the best carburetor cleaner?

Spray cleaners like Gumout, CRC, or Berryman work well for general cleaning. For heavy deposits, carburetor dip products provide more aggressive cleaning.

Should I use a rebuild kit when cleaning?

Rebuild kits include gaskets, needle, seat and sometimes jets. Using fresh gaskets during cleaning is ideal; the full rebuild components are necessary if the needle or seat are worn.

Why won’t my engine run right after carburetor cleaning?

Check that all passages are clear, jets are installed correctly, float height is correct and gaskets aren’t blocking ports. Also verify linkage reconnection and adjustment screw settings.

Can I damage a carburetor by cleaning it?

Yes, if you drill jets, damage needle seats, warp bodies with excessive heat, or strip threads. Use appropriate tools and avoid forcing anything.

How often should I clean my carburetor?

With proper fuel management (stabilizer, draining for storage), carburetors shouldn’t need regular cleaning. Clean when symptoms appear or during major service.

Summary

Carburetor cleaning restores proper fuel delivery and fixes most running issues caused by old fuel. The key is patience with the tiny passages - use proper carburetor cleaner and ensure all jets are completely clear. Always replace gaskets and diaphragms during cleaning. Prevention is easier than repair: use fuel stabilizer and drain fuel before storage.

carburetor cleaning repair