kuykw Posted September 10, 2007 Share Posted September 10, 2007 Hello all- I recently purchased a 77 xs400 and the bike is in pretty good shape - only about 5,500 miles. Since getting the bike I have replaced both air filters, both spark plugs, flushed front and rear brake fluid, and taken apart the carbs and cleaned them. For the carbs it was the first time I have attempted anything like this so I took it pretty easy and didn't take absolutely everything apart. I originally decided to take the carbs apart because I was noticing that one (right side when sitting on the bike) cylinder was running too rich. I was hoping that taking the carbs apart and checking/fixing any obvious problems would do the trick. But no such luck. Same problems again when I put everything back together. Anyway, it only seems to run rich at no more than 1/4 throttle. When riding I can feel the bike running rich when starting off from a stop, but after that 1/4 or so throttle the bike kicks in and feels strong again. I can see the sooty, black residue on the spark plug when I take it out after riding. Any ideas on the specific problem before I take things apart again? Could it be something other than the carbs? Thanks, Will Link to comment Share on other sites More sharing options...
Cy Welch Posted September 11, 2007 Share Posted September 11, 2007 Hello all- I recently purchased a 77 xs400 and the bike is in pretty good shape - only about 5,500 miles. Since getting the bike I have replaced both air filters, both spark plugs, flushed front and rear brake fluid, and taken apart the carbs and cleaned them. For the carbs it was the first time I have attempted anything like this so I took it pretty easy and didn't take absolutely everything apart. I originally decided to take the carbs apart because I was noticing that one (right side when sitting on the bike) cylinder was running too rich. I was hoping that taking the carbs apart and checking/fixing any obvious problems would do the trick. But no such luck. Same problems again when I put everything back together. Anyway, it only seems to run rich at no more than 1/4 throttle. When riding I can feel the bike running rich when starting off from a stop, but after that 1/4 or so throttle the bike kicks in and feels strong again. I can see the sooty, black residue on the spark plug when I take it out after riding. Any ideas on the specific problem before I take things apart again? Could it be something other than the carbs? Up through about 1/4 throttle the bike is running on the idle circuit. If it's running rich you need to adjust the idle mixture screw to adjust the mixture. At least your the idle mixture it easily adjustable unlike my 1980 which requires almost major surgery to get to the mixture screws. Mine also is rather lean, which as I understand is pretty normal for stock carbs on a 1980. Link to comment Share on other sites More sharing options...
kuykw Posted September 11, 2007 Author Share Posted September 11, 2007 Up through about 1/4 throttle the bike is running on the idle circuit. If it's running rich you need to adjust the idle mixture screw to adjust the mixture. At least your the idle mixture it easily adjustable unlike my 1980 which requires almost major surgery to get to the mixture screws. Mine also is rather lean, which as I understand is pretty normal for stock carbs on a 1980. Is the idle mixture screw the same as the "pilot screw" in the manual? The ones with the white cap on them? If so, I did try that adjusting that a good bit. For example - 1/2 turn out, 1 turn out, 2 turns out, etc. Then I would drive it around a bit, but I didn't really notice much of any improvement. Maybe I should try again. Does that screw adjust air or fuel? Link to comment Share on other sites More sharing options...
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