How to Troubleshoot a Carb on a Ryobi Weed Trimmer

Kurt Schanaman

Small two-stroke engine carburetors are specialized fuel delivery devices designed for the handling of a much smaller fuel flow into the cylinder of the engine. As such, they are simplified from a standard automobile carburetor, but don't let this simplicity fool you.

The small two-stroke carburetors require more cleaning and maintenance than their larger automotive counterparts. Here, we will investigate some of the most neglected maintenance procedures which will assist you in troubleshooting any problems which may arise with your small engine-based machine.

General Maintenance

  1. Remove the fuel tank lines from the fuel tank and then unbolt and remove the entire fuel tank from the equipment. When disconnecting the lines, inspect them for any cuts or cracks and also look for any which have collapsed. As the polyvinyl plastic which comprises most of these fuel lines ages it has a tendency to lose its support, causing it to collapse, the fuel supply to the carburetor becoming restricted.

  2. Remove the fuel filter from the hose on the bottom of the tank and inspect it to determine if it becoming too soiled. If the filter has restricted air flow through it, or appears dark-colored with debris clinging to it's exterior, install a new fuel filter and discard the spent one.

  3. Empty any remaining contents from the fuel tank and spray carburetor cleaner into the tank for about 10 to 15 seconds, shake the tank vigorously for about a minute permitting the cleaner to dissolve any sediment from the bottom of the tank, then drain.

  4. Before installing the assembly back onto the device, remove the carburetor end cap and spray two or three short bursts of carburetor cleaner into the carburetor. Inspect to ensure none of the other carburetor mounting screws are loose. If so, tighten them and then reassemble the cover and reinstall the tank, connecting all fuel lines as you go.

  5. Add no more than one ounce of Seafoam fuel treatment into the fuel tank and then fill with your standard two-stroke fuel mixture. Proceed to operate the equipment to determine if the maintenance has solved the erratic behavior of the machine. If you still have difficulty, please refer to the information below.

Ryobi-Specific Protocol

  1. The Ryobi line of small power equipment has traditionally used the Zama series of carburetors. As with any small two-cycle carburetor, the internal diaphragms have a tendency to lose their flexibility over the lifetime of the carburetor and may need to be replaced using a carburetor rebuild kit.

  2. Disassemble the housing from the equipment to expose the carburetor. Locate the identification tag on the carburetor and write down the serial number. If the number begins with a CU, then the carburetor is a Zama carburetor.

  3. Order a carburetor rebuild kit for your particular carburetor model and refer to the instruction sheet that comes with your merchandise. The Zama rebuild kits cost an average of $8 to $10 each and will provide you with a very inexpensive way to prolong the use of your equipment.

  4. For detailed information and servicing guides about your Zama carburetor, refer to the diagrams and technical information provided by Zama at www.zamacarb.com/tips.html


If you have determined that your carburetor requires a rebuild kit to be installed and you aren't confident in your mechanical abilities, please consult with any of your local small engine repair shops for assistance. Special Note: Some Ryobi string trimmers used the Wabro line of carburetors with the serial numbers beginning with a WT. All within this article applies, with the only difference being that you will need to purchase a Wabro rebuild kit rather than the Zama. Use Wabro's resources rather than Zama's at: wem.walbro.com/distributors/


Always use caution when using Seafoam, carburetor cleaners or any other solvents. Read the labels for full first-aid information and follow their advice strictly.