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The Water Cooler
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Honda Mower Carb Issue?
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<blockquote data-quote="joegrizzy" data-source="post: 3632959" data-attributes="member: 45524"><p>any ice, beit small two stroke, big bore single cylinder for gas operations, or 4-8 cylinder four stroke in your auto, needs the magic ~14.7:1 ratio of air to fuel to run. your auto, if it's obd ii or newer and has efi, uses a fancy o2 sensor with magnets to constantly fluctuate between rich and lean given your throttle inputs (which might also be controlled by the ecu instead of a wire on throttle body).</p><p></p><p>in an older carbed engine, the carb itself becomes the regulator of air-fuel ratio. it uses this really cool mechanism named Bernoulli's principle, which states that basically any flow that is passed through a constriction (smaller cross section of area) increases velocity and lowers pressure. it can apply to both liquids and gasses, it's even used in baseball to measure break on sliders and curves by those fancy sensors that amazon made.</p><p></p><p>so if you pass air thru a constricting tube (venturi), you can use the pressure differential created by the pressure drop to do things like suck fluid. this is how the droplet of gas gets regulated into the airflow from the suction phase of an internal combustion engine.</p><p></p><p>so if it's "surging" it's not getting the correct amount of air or fuel throughout the entire cycle of the engine. there is a mechanical linkage between the throttle selector, the actual throttle valve inside the carb, and the governor itself. the governor uses centrifugal force from the camshaft to put tension on this linkage, which the whole assembly can be referred to as the governor, as many auto stuff goes. the shaft that runs from the carb to the throttle spring does usually have a few spots for adjustment. essentially when the engine is running too lean/rich, the rpm's fluctuating are causing the governor to kick in and adjust the throttle to rectify the situation. like when the engine bogs going up a steep hill or cutting heavy grass. but since the carb itself may be clogged or not getting a good uniform dispersion of fuel, the governor cannot "find" the correct ratio it's "hunting" for, so you get a constant cycle of governor adjusting the throttle valve seeking to rectify the situation even tho it cannot.</p><p></p><p>it's a very similar issue to a vacuum leak on your car or truck. since that will mess with the air/fuel ratios, your o2 sensor will read this and freak out, trying to either send way too much fuel or way too little fuel to compensate. going that far away from the baseline of ~14.7:1 means on the next cycle it has to compensate that much more, creating a constant cycle of surging rpm's that seems to "hunt" for idle. upon acceleration or load on the engine, this surging can go away and the engine can run as normal, but when returning to idle the ecu can get fooled again by the vacuum leak and lead to surging. if you've ever f'd up replacing an intake or exhaust gasket or forget to replace a single vacuum line when doing auto work, you'll be very familiar with that mechanism. </p><p></p><p>replacing the carb is most likely the easiest solution. but a governor adjustment could certainly also perk it up. this video is really cool on how carbs work:</p><p></p><p>[MEDIA=youtube]toVfvRhWbj8[/MEDIA]</p></blockquote><p></p>
[QUOTE="joegrizzy, post: 3632959, member: 45524"] any ice, beit small two stroke, big bore single cylinder for gas operations, or 4-8 cylinder four stroke in your auto, needs the magic ~14.7:1 ratio of air to fuel to run. your auto, if it's obd ii or newer and has efi, uses a fancy o2 sensor with magnets to constantly fluctuate between rich and lean given your throttle inputs (which might also be controlled by the ecu instead of a wire on throttle body). in an older carbed engine, the carb itself becomes the regulator of air-fuel ratio. it uses this really cool mechanism named Bernoulli's principle, which states that basically any flow that is passed through a constriction (smaller cross section of area) increases velocity and lowers pressure. it can apply to both liquids and gasses, it's even used in baseball to measure break on sliders and curves by those fancy sensors that amazon made. so if you pass air thru a constricting tube (venturi), you can use the pressure differential created by the pressure drop to do things like suck fluid. this is how the droplet of gas gets regulated into the airflow from the suction phase of an internal combustion engine. so if it's "surging" it's not getting the correct amount of air or fuel throughout the entire cycle of the engine. there is a mechanical linkage between the throttle selector, the actual throttle valve inside the carb, and the governor itself. the governor uses centrifugal force from the camshaft to put tension on this linkage, which the whole assembly can be referred to as the governor, as many auto stuff goes. the shaft that runs from the carb to the throttle spring does usually have a few spots for adjustment. essentially when the engine is running too lean/rich, the rpm's fluctuating are causing the governor to kick in and adjust the throttle to rectify the situation. like when the engine bogs going up a steep hill or cutting heavy grass. but since the carb itself may be clogged or not getting a good uniform dispersion of fuel, the governor cannot "find" the correct ratio it's "hunting" for, so you get a constant cycle of governor adjusting the throttle valve seeking to rectify the situation even tho it cannot. it's a very similar issue to a vacuum leak on your car or truck. since that will mess with the air/fuel ratios, your o2 sensor will read this and freak out, trying to either send way too much fuel or way too little fuel to compensate. going that far away from the baseline of ~14.7:1 means on the next cycle it has to compensate that much more, creating a constant cycle of surging rpm's that seems to "hunt" for idle. upon acceleration or load on the engine, this surging can go away and the engine can run as normal, but when returning to idle the ecu can get fooled again by the vacuum leak and lead to surging. if you've ever f'd up replacing an intake or exhaust gasket or forget to replace a single vacuum line when doing auto work, you'll be very familiar with that mechanism. replacing the carb is most likely the easiest solution. but a governor adjustment could certainly also perk it up. this video is really cool on how carbs work: [MEDIA=youtube]toVfvRhWbj8[/MEDIA] [/QUOTE]
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