I am having some trouble with my 400ex. I warm it up for about 10 minutes of moderate driving in 1-3rd gear, not reving it up to much. Normally it will Idle super, clean and crisp. Now it is running choppy and barly idling. If I leave for 30 seconds idling, It literally puffs out Black smoke.Not much, but enough to see, and I give it a blip of throttle and you can really see the black smoke. then It start to idle rough again and does the same thing. I have noted before that it would puff out blue smoke shifting gears and coming back onto the throttle. but not black smoke at Idle. I use 10W40 honda oil. I am really not that hard on my 400ex. I am 17 and have poured all of my money into this bike thinking it was super relaible. Now, I am not so sure. I have had the valves checked after the break in. I was going to adjust them in the spring as well. I get my dealer to do the valves. I am thinking I have piston and ring damage.PLEASE HELP!!!

 

Sounds really rich. No matter how improperly adjusted your valves are, it won't cause your machine to smoke.

Don't be jumping to conclusions on the condition of your engine without any data, that's a good way to cost yourself a lot of money.

Have you changed jetting recently? Have you over oiled your air filter lately? Forget and leave the choke on?

When the gas is turned on, does fuel leak from the carb vent tube? You may have a stuck float, or something may be plugging the idle air circuit in the carb.

If it's this rich, don't run it until you figure out the source of the problem. It will wash the oil film from the cylinder wall and rings & cause premature wear.

 

I'm ganna ease your mind a little. Black smoke means you have a fuel problem, and blue smoke is oil/rings. How many hours are on it? I think just a jet change would fix your smoking, the only other option is to try Niqerette gum or the patch, they both help people stop smoking! LOL