fourstroke
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- Oct 15, 2019
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Hi all, this is my first post here. Very happy to discover such a treasure trove of expertise! :smile:
My trusty 20-year-old Honda HRB475C mower with GCV135 engine has been idling very poorly for some time. It was time for a new spark plug and air filter and I decided to have a go at cleaning the carburetor as well. It turned out to be much easier than I expected thanks to the excellent guides; the hardest part was getting it off in the first place. Curse those hose clamps!
As I was reinstalling the carb, I noticed something odd: when the throttle handle is set to idle, the throttle's butterfly valve remains open! I'd expect that to be closed, only progressively opening when I push the throttle handle forward. This retracts the throttle cable, rotating the governor assembly clockwise (viewed from the left), which pulls on the bottom of the rear governor arm via the spring, tilting the top of that arm backwards, which pulls the carb's throttle arm clockwise (viewed from top), opening up the butterfly valve.
However, that rear governor arm already assumes the "bottom forward, top backward" position by itself at rest. The spring going to the governor can just slide up in the spring's slot on the governor assembly. Nothing is broken, jammed or misaligned, it just settles naturally by gravity and/or the small throttle damping spring. I only undid the linkages at the carb's throttle and choke plate, the rest of the mechanism including the springs was not disturbed.
Is this behavior supposed to happen? I didn't pay particular attention to it before. Perhaps the engine vacuum flips the throttle closed but that seems like an odd design choice.
My trusty 20-year-old Honda HRB475C mower with GCV135 engine has been idling very poorly for some time. It was time for a new spark plug and air filter and I decided to have a go at cleaning the carburetor as well. It turned out to be much easier than I expected thanks to the excellent guides; the hardest part was getting it off in the first place. Curse those hose clamps!
As I was reinstalling the carb, I noticed something odd: when the throttle handle is set to idle, the throttle's butterfly valve remains open! I'd expect that to be closed, only progressively opening when I push the throttle handle forward. This retracts the throttle cable, rotating the governor assembly clockwise (viewed from the left), which pulls on the bottom of the rear governor arm via the spring, tilting the top of that arm backwards, which pulls the carb's throttle arm clockwise (viewed from top), opening up the butterfly valve.
However, that rear governor arm already assumes the "bottom forward, top backward" position by itself at rest. The spring going to the governor can just slide up in the spring's slot on the governor assembly. Nothing is broken, jammed or misaligned, it just settles naturally by gravity and/or the small throttle damping spring. I only undid the linkages at the carb's throttle and choke plate, the rest of the mechanism including the springs was not disturbed.
Is this behavior supposed to happen? I didn't pay particular attention to it before. Perhaps the engine vacuum flips the throttle closed but that seems like an odd design choice.