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Scooters - 125 to 300 => People 150 => Topic started by: swiftscoot on September 30, 2012, 06:10:14 AM
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I opened up my new People 150 today to tune the carb and remove the emissions junk, and saw that they do in fact cover the air fuel screw. Apparently it has to do with emissions. Anyway, my scooter was running slightly lean. It was jetted correctly, but it felt like it was getting too hot, and ran a little rough. So we busted off the cap, drilled a hole into the screw, which allowed us to stick a star bit in there to adjust it. A better way is to use a dremel to carve out a line, so you can use a flat head screw driver, but we didn't have a dremel.
To all y'all who have had trouble tuning your carbs, this is probably why. You can change jets for days, but it will never be spot on until you adjust the air fuel ratio along with it. To do that you'll need to pop the cap.
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Will you post a pic? I think mine is capped too. I can't seem to find the mixture screw.
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Are you sure that the air/fuel screw isn't for the idle circuit only?
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AFAIK, the air screw affects mixture from idle to about 1/4 throttle. From there, it plays a lesser role. Needle jet kicks in from there till about 3/4 throttle, then maximum fuel delivery is determined by the main jet. But all three fuel circuits add together to affect mixture from that point up. The pilot jet can't be changed without access to the air screw, as mixture will almost certainly need to be tweaked.
It is an "air screw", not a "fuel screw" meaning that counterclockwise turning adds air, leaning mixture, while clockwise turning decreases air, richening mixture. if it starts well, but has difficulty idling when hot, try adding 1/4 turn of air. A tach is helpful in tuning and setting idle. Stihl makes one for chainsaw tuning that is a proximity tach. You hold it near or against the body of the scooter lower front near where your right foot would be. no need to physically attach it to the spark plug wire. Stihl edt5 is discontinued, but a very good one. Also, the Tech Tach tt-20K gets good reviews.