Hi I have a ryobi rbc430sbsb 4-cycle brushcutter. When I use brus cutter it seems to start relatively easy and seems to work reasonably well but when switched off it seems to be dumping fuel out through the air intake filter. Does this indicate a problem with air/fuel mixture? And how can I fix this?
Your Carburetor Needle and Seat Require Cleaning or Replacement
Your float needle is not sealing against the seat properly allowing the gravity fed fuel to continue to flow threw your main jet as the fuel levels rise in your carburetor.
Some of these small carburetors have a diaphragm along with the float so you may also have to replace the rubber diaphragm where you would see a float system of fuel regulation. It would depend on the model.
Replace your needle and seat (and rubber diaphragm if necessary).
Double check the fuel lines for cracks/holes. I've had to replace the fuel lines on small engines every couple years due to the "new and improved" ethanol fuel. Normally I'd say replace the seat under the float needle but I'd say your engine is too small to have one.
If it's not fuel lines you probably will need a carburetor rebuild kit or just buy a new carb. For reference, I recently priced a carb rebuild kit for a 3 hp Tecumseh which was around $15. A complete knock-off carburetor was less than $25 on Amazon.