Does anyone know if their 400ex exhaust head pipes glow redhot when running at 1/4 throttle or above? Have never noticed this before but last night I was moving it in off the trailer and noticed this after it was warmed up and I was just holding 1/4 throttle on. The garage was dark and when I looked down at the engine they were glowing, but back at idle the glowing went away. If nobody has noticed this try it tonight and let me know if yours does this too.

Gasman

 

No, I have never noticed that ever happening on my 400ex. You might want to check and see if your headpipes are loose from where they bolt onto the motor. If that's the case, tighten them up fast because all of the hot exhaust heat coming out of the engine will burn your valves up in a heart beat!!!

 

You may want to check your plug, you may be running a little lean. It is normal for is to glow ever so little right after a hard ride or if it is highly modified but not after a spin on a stock bike.

 

I'll take a educated guess. Your 400's new and u know little about it? Same happened to mine when it was new(last spring) Your only prob is that its running lean. It doesn't take long for them to become a "cherry like color" You can notice it in the day if u look for it. If u are new with it, take it to your dealer and have him re-jet it. Seems a bit odd that its running lean now that its fall. But if your bikes new that is definitly the problum. This doesn't happen to ALL stock 400's so not everyone needs to go start there bike up at night to see if there exhaust become a weird red glow.Hope i helped
Ben #16

 

Thanks for the input. I suspected it was lean. The bike is my wife's one of the first 400ex's on the market. But basically new (less than 10-12) tanks of gas. Has always run perfectly without problems. It has been sitting for about 6-7 months and possibly partially varnished-up some of the jetways leading to a lean run? Any way it's going in for a checkup tomorrow. I don't do a whole lot of messing with it as my LRD 330R usually keeps me occupied.

Thanks
gasman

 

My 2001 400ex also has the same thing going on and has for the last 800 or so miles. It seems to happen if you turn the gas off and run it till it quits. This is something I have done with all my gas engins so that if they sit for long periods of time the carburator does not get gummed up with old gas. The first time I noticed it I was quite alarmed so I called the dealer and I was told to check my spark plug for signs of running too lean. Since then I have compared my plug to 3 or 4 other 400s and mine looks the same as thiers. My bike is stock. If you have played with the jetting or modifided it in any way you may be running it too lean. If you can, compare your plug to another bike. Hope this helped.

 

I wouldn't do that if I where you. When you turn the gas off and run the engine you starve the carb of gas an run really lean, you might even hear the idle go up. If you had just started the bike and ran if for a few mnutes this wouldn't be a problem but if the weather is hot and you just pulled in from running it hard you could run the risk of engine damage, especially on highly modified engines.

 

Thanks guys for the info. I will share with you what the Honda dealer found. I took it in for them to check this out and they found about... nothing... except that it was running a little rich, minor carb adjustment and it does have a little improved throttle response the pipes still glow. However they said that a lot of the bigger 4-strokes (YZ426?,400ex, ect.) will do this with their pipes and that there is nothing abnormal going on. When the Yamaha dirt bike came out apparently several of them were brought in for the same thing and after going over them and consulting Yamaha this was deamed a normal condition so ride'um and have fun.