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ceesneezy

Walbro carb tuning on 2 stroke trimmer

ceesneezy
13 years ago

I am new to carburetor tuning. When tuning a carb on a two-stroke machine such as a trimmer, what does it mean to adjust throttle or air mixture screw until it "four cycles"? And what does this sound like? See the paragraph below which I found online about Walbro carb tuning on 2 strokes. Also does the same method apply to tuning a 4 stroke engine such as your typical lawn mower? Thanks

"Set the lowend & highend needles to about 1 3/4 to 2 turns each. Choke the carb or prime it, until the carb is wet. Fire up the engine and let it warm up. Let's set the topend first since it's the easier of the two. Go to full throttle. Adjust the topend needle for peak RPM. Leave it wide open for about a minute to see if it changes any. Should the engine go lean, open the lowend needle slightly, if this dosen't work... you will have to adjust the needle valve inside the carb.( I will explain this later) If the topend runs OK, then slowly pull the throttle down until the engine begins to "four cycle" hold the throttle there. Adjust the lowend needle until the "four cycling" barely stops. Now lower the throttle more until it "four cycles" again, and adjust the lowend again. Keep doing this until you reach full idle. Now, from full idle begin to throttle up until the engine starts to bog or hesitate. Open up the lowend needle just enough to eliminate the bog or hesitation.

When this is done right, you will be able to set the throttle in any position and it won't four cycle, plus you will be able to transition from idle to full power without any hesitation at all. Now, for easy starting it's best to have the lowend a little rich and it will four-stroke a little."

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