How to Troubleshoot a Carb on a Ryobi Weed Trimmer

Updated February 21, 2017

Small two-stroke engine carburettors are specialised 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 carburettor, but don't let this simplicity fool you. The small two-stroke carburettors 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.

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 carburettor becoming restricted.

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-coloured with debris clinging to it's exterior, install a new fuel filter and discard the spent one.

Empty any remaining contents from the fuel tank and spray carburettor 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.

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

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 behaviour of the machine. If you still have difficulty, please refer to the information below.

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

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

Order a carburettor rebuild kit for your particular carburettor model and refer to the instruction sheet that comes with your merchandise. The Zama rebuild kits cost an average of £5 to £6 each and will provide you with a very inexpensive way to prolong the use of your equipment.

For detailed information and servicing guides about your Zama carburettor, refer to the diagrams and technical information provided by Zama at


If you have determined that your carburettor 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 carburettors 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:


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

Things You'll Need

  • Screwdriver set
  • Socket set with both standard and metric sockets
  • Needle-nose pliers
  • Seafoam fuel treatment solution
  • Can of carburettor spray cleaner
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About the Author

Kurt Schanaman has had several editorials printed by the Star-Herald Newspaper publication in Western Nebraska. He attended Western Nebraska Community College.