The numbers cast into the throat of the carb is the venturi size in 64's of an inch.</p>

20 = 20/64" = .32125" = 7.9mm venturi.  A very small carb.  The weedies come with small carbs and often low port timings so that they can be run at full throttle and even if the string breaks they won't rev high enough to hurt themselves.</p>

The Ryobi responds well to an 11mm venturi carb, which has a "28" casting number in the carb throat.  A "26" carb will work fairly well on a Ryobi too if you happen to have one of those.  I use 11mm.</p>

AV8TOR</p>

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