I have a 99 400EX with a K & N power kit. Lately it's been blowing blue smoke when I'm accelerating but doesn't do it on idle or just putting around. If it helps any, the main jet is the stage 1 called DJ142. Can anyone help me diagnose this problem, would be much appreciated.

www.geocities.com/hulioni

 

I have several friends with 2000 stock ex's and they all blow blue smoke when you get on it real hard while the quad is under a load. I have 99 with a k and n and 170 main and i have the problem to. So far it hasn't cause any bad side effects.

Mr_400eX

 

This is a common problem with the 400EX.

An air cooled engine that sees extreme RPM's and operating temperatures such as the one in a 400EX is very abusive to engine oil.

I believe that it is breaking down the oil. My solution: Run a heavier weight oil, I run 20w50 in mine, and it doesn't smoke anymore, although it used to. Do it before it's too late, consider the smoke a warning that your engine oil is not doing what it is supposed to be doing. If you let it go too long it will only get worse.

I am getting ready to switch to Mobil 1 15w50 synthetic. We'll see how it does. Oil's such as Redline state that their lighter weight oils have better film strength than heavier weight conventional oils. This may be an option to explore as well.

 

I have owned 4 honda RFVC engiens but all in XR's and I have never seen one smoke, even my XR400R doesnt smoke and it is nearly the same engine. But I have always ran 20W50 snythtic HP-4 oil.. once I got mad after loosing a race and held it wide open in nutural when it was 100 degrees out side after a long hard 40 mile ride and no smoke. Personly as a mechanic I wouldnt own a bike that smoked, even if it is harmless
Joe

 

I use GN4 10W-40 and I don't have any smoke except when it is cold outside and the bike is warming up (on choke).

 

I have a buddy who has a 2000 XR400 - his doesn't have the smoking problem either. Although you can tell by the header pipes that, that engine doesn't run nearly as hot as my 400EX (his pipes are golden with a tinge of blueing, where mine are a very deep purple). The 400EX has to pull a much heavier load than an XR - especially when ridden hard. It's pulling a lot more weight, and has a lot more tire on the ground, both of which are very hard on the engine and oil.

I noticed mine blowing out a little puff of smoke just after I considered it "broke in" (I have had a lot of bikes, and built several engines and know how to properly break one in). I was very unhappy, it had no reason to smoke.

Having seen this before on the 400EX, I began trying to figure out why. My only explanation was the oil. I switched, and no more problems. I caught it quick though, I have a friend that let it go a while before switching to Klotz synthetic, his still smokes and gets worse every time I see it. Although I just saw a puff out of it on my last ride, alerting me that the oil is in need of changing... again. It sure doesn't last long when ridden really hard. That's why I am switching to synthetic, higher film strength and more resistance to breaking down, to name only a couple of the advantages in an engine like mine.

BTW... The factory fill is some weight of Castrol.

The moral of the story... Always use the highest quality motor oil. Also I wouldn't recommend anything less than 10w30 on a bike that gets ridden hard at all. 10w30 will be more resistant to breaking down than 10w40 due to it having less viscosity index improver. I personally will never run mine on anything less than a 15w-something again. I always give the bike a good warm-up as well, especially when running the thicker oils.

 

for a canada rider @-30 degrees 10W30 is fine but Man not for summer rideing. I stuck our meat thermoter in the oil after a long super hard ride on my XR250 and it went past 300 degrees!!! Snythtic 20W50 is the only way for a hard pulling EX. Blue headers..hmm sounds like she is running lean to me, Id pick up a larger main and raise the needle and see what that does.
Joe

 

Yep that's my whole point, the 400EX runs very hot and is extremely hard on engine oil, even more so than your XR250. A heavy weight synthetic is the best way to protect it.

Yes, the 400EX does run lean. Honda was even kind enough to tell us in the owners manual (govt emmissions regs here in the US) that they jetted it lean. I am getting ready to re-jet mine now that it's warming up a little outside. I just hate messing with carbs, so I've been putting it off (I dislike carbs so much, I have fuel-injected 2 of my street vehicles, the others are already injected).

 

Isnt that the truth, how hard can it be to put a injector in the intake boot and a small computer on top of the airbox with and a tiny fuel pump with a TPS sensor. just think, no choke, no high altitude re-jetting, just kick and go

 

I hav seen this on the trails w/400EX's. They all do it that I've seen. Blue smoke is OIL BURNING. In my opinion there are 2 reasons for this (1) Nobody runs the proper oil, they run what daddy always put in the car. (2) The 400EX, although a good Quad, still needs refinment. You can't just drop a XR motor into a new quad frame and expect it to be perfect. SHAME ON HONDA! This motor can't just go out and pull a quad around like it does a dirt bike without some changes.

I suggest senthetic oil or Havoline 20w50 to solve your problem if it's not already too late. Also, keep it changed regularly and if you see a hint of smoke, go home to change it. You can heed the advise or not. But if you don't, I think you'll be in for a pre-mature REBUILD.

Oh, don't feel bad, other quad producers are going to make the same mistake in '01.