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Beta Rev 3 270Cc 2003


ryan31199
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How many turns should the air screw on my Mikuni carb be out? I have mixed the fuel 75ml too 5 litres of petrol. Bike is running rich and smoking a fair bit. However the air screw is all the way in. I have just bought the bike so not familiar with how the carb should be set up. Thanks in advance

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The mixture screw should be between  1 turn out and 2.5 turns out. Your fuel oil mix is somewhere close @ 1.5%  ( 66.67 to 1 )

A lot of people have good results @ 1.25% oil to fuel mix ( 80 to 1 )

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If your air screw is all the way in it's probably time for a disassemble and clean of the carb. With the air screw all the way in the bike should bog badly off the bottom. If it seems to run OK with the mixture screw in all the way it could indicate a blocked pilot jet. A lot of times riders will just crank up the idle speed but it makes the bike harder to ride in the slow stuff. If you pull the carb pay close attention to the pilot jet circuit. Pull the whole carb apart and use compressed air to blow out the jets and carb body. Note which jets are installed. The typical pilot size used around here near sea level was a 27.5. Stock was a 30 but the suspicion was always Beta put that in so the bikes would break in with the slightly richer jet off the bottom. There's also considerable information on stopping the fuel piddle problem of the Beta in the Mikuni thread pinned in this forum. My preferred method is to just nip a hole in the vent tubes above the float bowl. Also look at setting the float level and the float travel. This is done by adjusting the brass tabs on the float lever thingy.

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The bike runs fine and the idle speed was a little fast when I bought it. I've slowed it down since but not adjusted the screw. I have had the carb off and set it all up as it should be and the jets didn't seem blocked. Not yet ran the bike as the fuel tap was broke and just kept flooding the crank out. Hopefully will be sorted now. I'm going to undo the screw and see if it stops it running rich and smoking as much

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