cwill83247 Posted September 4, 2013 Report Share Posted September 4, 2013 I have read previous posts but not sure I am understanding fully.. Hoping someone can give me a idiots explanation My understanding The smaller screw adjust amount of air if I screw it in means less air but higher fuel to air so this is running rich ??? On gas gas pro you only have an air screw The bigger screw just adjusts tick over and doesn't affect rich or lean running And finally it's better to run rich than lean Hope I am on right lines cheers chris Quote Link to comment Share on other sites More sharing options...
mr neutron Posted September 4, 2013 Report Share Posted September 4, 2013 (edited) You're correct; The bigger screw effects tickover (idle), and has no effect on the mixture. More air equals a lean mixture, and more fuel equals a rich mixture. Getting the correct balance is key. I think a slightly richer mix makes the bike a little slower reponding off idle, as in when you just barely open the slide/accelerate. A leaner mix makes them respond quicker. Within reason, if you're reasonably close to that 14:1 (or whatever it is, I forget the "optimum" air to fuel ratio....), being a slight bit lean or rich won't hurt anything. It'll have more effect on throttle response than engine longevity. Now, if your talking mainjet/wide open circuit, this correct mixture is more important (to engine life), and being slightly rich is normally somewhat more desireable than being too lean. My bike has a Dellorto carburetor, which has a fuel screw. The bikes with Keihin PWK Carbs have an air screw I believe. Here's a rough rule of thumb, if you don't know which carb you have: The Keihins will have the air screw closer to the "bell" end of the carb. It will be at the air inlet end of the carb. Screwing that screw out will make the low speed circuit leaner; screwing it in will make it richer. It regulates the amount of air you get for the idle/low speed circuit in the carb. The Dellorto carbs will have the mixture screw "in front" of the slide, sorta, up by the intake manifold. Screwing this screw OUT makes it richer, and IN makes it leaner. Just the opposite of the air screw. It regulates the amount of fuel you get in the idle/low speed mixture. Hope this helps! Jimmie Added in EDIT: I wasn't sure which carb cwill has on his bike, which is why I typed what I did above here. If any of it is not accurate, or wrong/incorrect/stupid, I hope someone will chime in to correct me. It's been my experiences that bikes with a fuel mixture screw tend to have the mixture screw located the way I described (close to intake manifold end of the carb), and carbs with an air mixture screw tend to have that mixture screw located at the opposite end of the carb (closer to the air inlet end). This has simply been my own experience. In life, there's probably exceptions & variations out there waiting to prove me wrong...... Edited September 5, 2013 by mr neutron 2 Quote Link to comment Share on other sites More sharing options...
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