Trouble with idle on 1977 xs400


XS400 New Member
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Ontario, Canada
Hoping for some insight. New member and love the forum. Recently bought 1977 xs400 but the bike doesn’t seem to want to idle off choke. The carbs have been cleaned, replaced a stripped pilot jet, cracked diaphragm and sprayed carb cleaner in every hole along with compressed air. I also installed an electronic ignition system from MikesXS and replaced the points system. I followed the steps on the site to install that.

It started up cold and first shot with the electric start. Started it yesterday and today no problems. (i also replaced the plugs and boots fyi) great spark and coils all check out with my multimeter.

The issue im having now is that the bike does not really idle when i push the choke in all the way. It will idle with it in the middle position between 2-3k rpm when cold then it starts to kick up to 5-6 once it got warm. As soon as i push the choke in it falls down to 1.5 for a couple seconds then dies.

Usually if it needs some choke to idle, your idle circuit is running too lean. I had to clean my carbs three times before I got any idle speed change by adjusting the idle mixture jets. I also needed to use single strands of copper wire to ream out the jets and all the passageways including the idle jet passages. For example, my pilot jets seemed clean, carb clean sprayed through it, but by using the copper wire strand, I actually pushed more crud out of the orifices! If you are sure everything is clean start by carefully bottoming out the idle mixture jet in, the turn them out 2 1/2 turns initial. Then start backing out the idle jets like a 1/4 to 1/2 turn at a time to raise the idle then lower the idle speed screw to bring the idle speed back down and keep the carb from running off the main circuit. Keep repeating that until turning the idle jet screw lowers the idle, then turn it back in a 1/4 to 1/2 turn. Finally reset the idle speed screw to 1200 RPM.