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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?

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    Sounds like a carburetion problem to me ... not necessarily the mixture, but possibly the float or needle valve, but I don't even know if this type has a float in it. Is this brand new or has it been around for a while? IOW: Is this quite new behavior, or has it been doing this for a while?
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Sep 11, 2016 at 19:09
  • There is only two adjustment screws i can find on the carb the first is just speed which simply presses on the throttle arm the other is located on the top of carb near throttle and air intake. I adjusted this screw slightly a while back as engine was very rough idling and stalling plus was revving up then dying at full throttle. Seems to run better now just spews fuel through air filter after switching off engine
    – R.Bevan
    Commented Sep 12, 2016 at 4:17

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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.

Short Answer

Replace your needle and seat (and rubber diaphragm if necessary).

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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.

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