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I have tried many technicians but none have solved my problem. I had problems in the past past, but one day my bike started to make a noise while opening the throttle when cold after about 50km/h speed. The noise sounds like the choke is on. After some months it was getting worse. When hot it, seemed ok. One day I could hardy go over 30km/h anymore.

I cleaned the air filter two years ago. I told the technician that I suspected the air filter might be the problem, but he told me no! He told me that because I had done boring he put a bigger main jet! Then it was running ok but after driving when it stopped I had a drop at idle. Next day I had to try 30 times to start it manually. Then it turned off on its own when braking or at a stop. Once it warmed up it seemed okay. The noise was still there. They told me that it was normal to hear noise when cold. I had to wait 5km in order for this noise to stop. Then next day it got worse. I tuned the carb, then it was fine at idle, and it started great. But after driving fast 80-100km/h, when I was stopped it turned off.

The day after that things got worse. I couldn't go faster than 30km/h again and I heard the noise. Fuel consumption was 2x because of the main jet. I decided to fix the problem myself again. I removed the air filter box and it had some insects inside and seemed black. I installed a cone air filter I had from previous owner. Then although cold start I had problems but that noise stopped and although cold it could go fast without problems and no noise. But throttle response was weird. I guess that air/gas mixture is screwed ? Should I go back to my old main jet and buy a new filter? And why does it turn off when I stop ?

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What does the spark plug look like? Done any plug chops yet? I wouldn't mess about with the mixture (which you are doing) without testing the changes either using a wideband O2 sensor (probably not going to work well on a scooter) or at least some plug chops with a couple of fresh spark plugs. –  Timo Geusch Dec 21 '12 at 1:43
at morning i'll check how it looks. As i read/know i should check after running full the color ?Does it work when running at 1/4? –  Parhs Dec 21 '12 at 2:24
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