Rich carbs

BobJJ · Posted: April 27, 2007, 10:03 am Post subject: Rich carbs

Hi all, I have a slight problem. I have a 75xs650B with 38 carbs. I installed pod air filters and open mufflers about 1 foot long. Problem is it's running very rich, black soot and smells rich. It starts and runs great. If I accelerate slow it moves great, but do quick throttle noise goes up but bike not. Clutch not slipping.
I installed 130 main jets and 47.5 pilot jets, I didn't move the needle clip on the slides though wondering if this could be it. I turn air screws in and cylinder speeds up when the screw seats bottom, so I turned them out 1 1/2 turns just because. Did this on both sides. Thanks for all help

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

What kind of pods are you using? If they're the $12 cheapies, then they're probably blocking the air ports around the intake bell. All fuel and no air equals rich running. Try a test run with the filters removed.

Your mixture screws (these carbs don't have air screws) should be set for fastest, smoothest idle speed. The initial setting point for your model is 3/4 of a turn out. This is just a suggested ball park setting to get you started. From there, work the screw in/out to find the ideal spot. At twice the suggested setting, you're probably a bit rich. This being a true mixture or fuel regulating screw, the more you turn it out, the richer you make the idle circuit. A larger pilot usually requires less opening of the screw, about 1/4 turn per size increase.

When you increase pilots and mains, they bleed over into the midrange and make it richer. Many times you need to drop the needle (lean it out) to compensate. Stock, your carbs should have a 4N8 needle with the clip in the 4th slot from the top. Move the clip to the 3rd slot to lower it and lean your midrange.

Here's the air ports you may be blocking .....

BobJJ · Posted: April 28, 2007, 12:39 pm Post subject: Re: Rich carbs

Thanks for the help. The air cleaners are the cheap ones, I pulled them off and then the rubber boots off the air cleaners and put the boots on, the 2 small holes were open but the top long one was covered, a little work with the jack knife and they were open. I also lowered the needle one notch to 3. Took it out for a test run, Runs great!!!!!!!!!!!!!!! I got 53.9 mpg in town running rich now lets see what happens. Again thanks alot.

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