How to Repair a Small Engine Carburetor

Small engines, typically found on lawn mowers, ATVs, generators and pumps, have designs and components very similar to other four-stroke engines. They differ only in the miniaturization of the parts. The fuel, electric systems and compression needs remain the same. Diagnosing and repairing small engine carburetors need not be a highly technical mystery, especially when you have familiarized yourself with the basic components and their purposes. All you need to fix a small engine carburetor are a few tools and some basic steps.

Things You'll Need

  • Small engine repair manual
  • Socket set
  • Ratchet wrench
  • Screwdrivers
  • Carburetor cleaner
  • Rags
  • Penetrating oil
  • Drain pan
  • Small ruler
  • Compressed air source
  • Use a socket or screwdriver to remove any cowl or plastic plenum that impedes access to the carburetor. Unlatch any hood device by unclasping the snaps to gain access to the carburetor. Use a socket to remove the air cleaner housing that sits over the carburetor, or use a screwdriver to unscrew the cold air intake hose clamp to the carburetor throat.

  • Check the position of the choke plate that swivels open and closed in the top of the carburetor. Move the linkage back and forth, making sure the choke plate has full range. Spray penetrating oil on the choke butterfly valve, its shaft, and the outside choke linkage and cams. Work it open and closed several times.

  • Refer to your engine repair manual for the location of the idle mixture screw on the carburetor. It will have a slot-head screw that attaches to the side of the carburetor. Remove the screw with a screwdriver and clean the tip of the screw needle shaft with carburetor cleaner and a rag. Keep the spring intact on the screw, as you clean it.

  • Pull the small fiber gasket out of the mixture screw seat and examine it for cuts or crushed sides. replace it if damaged. Replace the idle screw in its seat, then turn it all the way in, clockwise. Turn it 1 1/2 turns out, counterclockwise, for the initial adjustment setting.

  • Shut the fuel supply valve off. Remove the throttle linkage cable attached to the carburetor cam with a screwdriver. If equipped with a governor rod, unclasp the retaining clip that holds it and push the governor road aside. Use a screwdriver to remove the fuel line hose clamp. Remember the position and fastening location of the parts. Use a socket to loosen and remove the carburetor mounting bolts to the engine.

  • Pull the carburetor from the engine block. If the carburetor mounting gasket to the engine has cuts or burn marks, scrap the old one off with a screwdriver blade and clean it with carburetor cleaner. A defective gasket will cause a major vacuum leak. Insert the new gasket when you remount the carburetor.

  • Unscrew the float bowl drain plug and let the gas drain into a pan. Use a screwdriver to remove the screws on the float bowl and pull the float bowl free. Do not disturb the float bowl gasket. Let it remain intact. Touch the float to make sure it has not filled with gas and sunk. If the float has gas inside it, replace the float.

  • Tilt the float bowl upside down and let the float hang from its swivel hinges. Consult your engine manual for the proper drop distance for your float, in inches. Use a small ruler to gauge the distance from the bottom of the float to the top of the hinge mechanism.

  • Bend the tab on the float to change the drop distance of the float, using a small flat-head screwdriver. Notice the float needle connected to the float lever tang. The float needle closes off a seat in the carburetor. Spray carburetor cleaner up inside the float needle seat.

  • Spray all of the small orifices and pickup tubes in the float chamber, using the high pressure tube nozzle on the carburetor cleaner. Spray the inside of the carburetor throat, including the small air bleed holes. Wipe out the float bowl with a rag. Hold the float closed with your hand as you use a high pressure air source to blast the carburetor inside and out.

  • Reassemble the carburetor, attaching the float bowl first, and tighten the screws with a screwdriver. Place the carburetor back on the engine block and use a socket to tighten the mounting bolts. Remember to replace the carburetor-to-block gasket with a new one, if it needs it.

  • Reconnect the governor linkage arm and its retainer clip. Use a screwdriver to tighten the throttle cable in the same adjustment location you removed it. Reattach the fuel line and tighten the clamp with a screwdriver.

  • Replace the air cleaner housing or cold air intake hose, and tighten it with a screwdriver. Turn the fuel valve on. Activate the choke. Start the engine and let it warm up. Deactivate the choke. Adjust the idle mixture screw until you have maximum rpm (revolutions per minute). Next adjust the idle speed screw on the linkage, for a smooth running engine.