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Author Topic: Help! 400ex Smoking  (Read 10180 times)
hondarider95
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« on: January 16, 2007, 11:23:16 PM »

I just bought a 400ex, and it is smoking quite a bit. I haven't ran it long enough to see if the smoke will go away, I can do that tomorrow. It starts right up, and runs fine. So I think the piston/rings are ok. I was told it is probably the valve seals. If it is how hard are they to install? What do you all think?

Thanks
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xr100racer
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« Reply #1 on: January 17, 2007, 11:19:35 AM »

What color is the smoke? If its oil and your valve seals are bad then it will smoke on start up and then go away. If its your rings then it will smoke and not stop. The bike will still run decent with bad rings and since you just got it you wouldnt notice a performance decrease since youve never ridden when the rings were good. Check the compression, that will tell you if the rings are bad.

It could also be running rich (choke stuck on, clogged air filter, too big of jets, etc) if thats the case then the smoke would be black since you are not completly burning your fuel.

And it could also be steam that you are seeing, this would be the most unlikely of problems that you could be having from your description. Steam would be from a blown head gasket and antifreeze boiling in the combuston chamber and coming out the exhaust. This will cause your bike to run horrible.

That pretty much covers it, hope this helps.
« Last Edit: January 17, 2007, 11:26:26 AM by xr100racer » Logged
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« Reply #2 on: January 17, 2007, 11:35:10 AM »

not to rain on your parade buddy, but the 400EX is air-cooled.

but your other options are spot-on.

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xr100racer
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« Reply #3 on: January 17, 2007, 11:38:11 AM »

Sorry, wasnt thinking. Ignore that one. Im used to my bike - water-cooled
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hondarider95
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« Reply #4 on: January 17, 2007, 12:38:09 PM »

Ok, its white smoke. I just went out and ran it for like 25min. Its smokes less and less as it gets warmer, but even once it is all the way hot it still smokes, especially at high rpms. It doesn't have the exhaust tip on, I dont know if that makes it worse? Could it be that the valve seals are so bad that they still leak when hot? It runs perfectly. My friend has a compression tester, I will try and see how my compression is. Let me know what you all think.

Thanks
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xr100racer
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« Reply #5 on: January 17, 2007, 03:20:44 PM »

Jetting could be lean. Do this: drive it in 2nd or 3rd gear and get the rpms preety high then let off but do not pull in the clutch. Let your motor slow you down via compression braking. If it pops and backfires then your jetting is lean.

If the motor/pipe/filter are all stock and the jetting has never been changed then its possible that since the spark arrestor was removed it increased your air flow. When you increase air, you also need to increase fuel.

More air than fuel = lean

More fuel than air = rich
« Last Edit: January 17, 2007, 03:24:35 PM by xr100racer » Logged
hondarider95
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« Reply #6 on: January 17, 2007, 04:57:53 PM »

Ok, I just did that and I got a couple of pops while doing it in 3rd gear none in 2nd. I got a 250ex too, and it looks like the same size exhaust tip, so I will see if it fits and if it does, I can test if that makes it smoke less. Also I will go ahead and get the valves right on, see what jets are in the carb, and clean it while I am in there. Then see what happens. Let me know what you all think. Could it being lean make it smoke alot?

Thanks
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xr100racer
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« Reply #7 on: January 17, 2007, 05:15:14 PM »

I dont think it would smoke alot if it only popped a little, try the tip from the 250 and see what happens. Clean the carbs if that doesnt help. Having your valves not adjusted perfectly would not make it smoke, as long as they are not ticking then I wouldnt worry about them, although it may be about time to adjust them. Listen closely to the rocker box/valve cover

Try this - run it with the choke on a little and see what happens, not to the point of blowing black smoke though. If you can get it just right where there is no smoke then you will know if it is a fuel mixture problem
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hondarider95
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« Reply #8 on: January 18, 2007, 12:09:32 AM »

I'll try that choke thing tomorrow. Also There are two out of three screws stuck in the exhaust (the ones that hold the tip on). I tried getting them out a little today, I will get an easy out on it tomorrow, and if that dont work I'll drill it out. But then I'll try the exhaust tip.

I think the bike came from georgia, could it have different jetting cause of that? Would that make it leaner or richer?

What does ticking valves mean? I didn't notice any ticking valves. I did notice a little cam chain noise, not alot though. I got the bike cheap enough that even if I do have to do a complete rebuild, I will still be ok. I think I should have time to do some stuff to it tomorrow. Here's what I am going to do:

-Clean carb (see what jets it has)
-Adjust the valves
-change oil+oil filter
-get those screws out of the exhaust
-test out the 250ex exhaust tip
-try and get my friends compression tester

What is most likely causing this? What is most common?


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gery350
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« Reply #9 on: January 18, 2007, 12:24:10 AM »

ok heres the nickel tour on smoke.
white smoke-water
blue smoke-oil
black smoke-rich

a lean condition will not cause smoke, more then likely you are burning oil.
valve adjustment will not cause smoke.
you either have bad valve seals or rings(or a combination of both.)
excessive smoke when cold is usually a symptom of valve seals but could also be caused by rings.
since it does smoke more at high rpm more then likely youwill need piston rings.

playing with the mixture will do nothing for the white/blue smoke.

good luck.
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hondarider95
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« Reply #10 on: January 18, 2007, 12:32:40 AM »

Ok, so should I go ahead and order piston and rings or just rings? What else should I replace while I am in there? It is 5 years old, so it is probably on its original top end. Will I be able to replace with std bore piston? Let me know what you all think.
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« Reply #11 on: January 18, 2007, 05:31:16 AM »

 it sounds like you are burning oil
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« Reply #12 on: January 18, 2007, 08:40:46 AM »

get your friends compression tester and see what that says first before you tear into the engine.

As far as boring out the 400, I would not on that age unless you want to start blowing headgaskets,,,,the 400's have an interesting problem around that age that the metal gets weak from the increased heat and pressure and will actually allow the head to stretch a little so much that you blow a headgasket.

don't get me wrong, great bike,,,,I love mine, but I would repair it and have fun with it stock for now.

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hondarider95
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« Reply #13 on: January 18, 2007, 10:05:59 AM »

Ya, I would not want to bore it unless I have to, because of cost, and in many cases it decreases the value of the bike, cause people assume that it was raced or abused.

I'll do the compression test and let you all know the results. If it is a 2001, do you think I need a piston and rings or just rings? What determines if you need a piston as well?
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« Reply #14 on: January 18, 2007, 10:15:46 AM »

you need to check the tolerance allowed between piston and cylinder with a feeler gauge.
i dont know what it should be but once taken you'll know if boring is required.
maybe atp racing can tell  ya.
you can probably get away with just new rings and seals.
if the piston isnt too much i would replace it as well.
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hondarider95
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« Reply #15 on: January 18, 2007, 12:43:08 PM »

If I didn't replace the piston, what could happen to it if I just used the original one with new rings? I drilled out those exhaust bolts and tried the tip from the the 250ex, and it still smoked (as suspected), but I dont think it smoked as much, and it was extremely quiet. I'll try and get the compression tester from my friend, and test it this evening. I will let you know the results.
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xr100racer
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« Reply #16 on: January 18, 2007, 01:24:08 PM »

It certainly does sound like rings but he said its white smoke. ? I said it could be running lean but for some reason I was thinking about a diesel engine, diesels blow white smoke if theyre running lean. Sorry. The only reason for it to be blowing white smoke is burning water - anitfreeze. But this is air-cooled.

So your either blowing black smoke and running really rich to see a large amount of it. Or its oil which would be your rings. Rings are most likely your problem. You may not need a new piston, you may be able to replace the rings on the stock bore. Youll have to see what the cylinder walls look like. My advice would be to take the cylinder to a machine shop and ask their opinion or a mechanic. If you do need an overbore then you will need to get a piston that is .5mm or 1mm larger in diameter so you can use the origional sleeve. Then you will need to get it bored to the new piston's specs, gap the rings, and install.

Valves need to be adjusted at a regular interval such as 10, 20 hours or something like that depending how you ride. The ticking is caused by the rocker arm having too much clearence with the top of the valve. They move up and down in unison with each other but have to have a set distance apart from one another. Too much clearence and they tick.

If you are hearing timing chain slap for sure then you will want to replace that while you got the motor apart. I believe on your bike that the timing chain has an automatic tensionor so its not something you can adjust. Once it has worn to the point where the auto tensionor can not take the extra slack out of it, its time to replace.
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hondarider95
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« Reply #17 on: January 18, 2007, 01:46:34 PM »

Looks white, but maybe it is light blue? I guess the compression test will tell alot. Since it is only a 2001 it probably wont need to be bored right?
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xr100racer
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« Reply #18 on: January 18, 2007, 01:54:38 PM »

It would be very odd for it to be white.

Do the compression test and that will tell you. Your bike could have been ridden alot since 2001. Its not like a car, it wouldnt be likely for an average  car to need a rebuild if its only a 2001. But a bike, this is not unusual
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hondarider95
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« Reply #19 on: January 18, 2007, 03:42:32 PM »

Ok, my friends compression tester doesn't have the right fitting. Can I get a compression tester or just the fitting at like auto zone or something? Let me know ASAP, so I can try and get one today.

Thanks
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MuddFreak77
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« Reply #20 on: January 18, 2007, 03:46:07 PM »

Autozone should have one
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« Reply #21 on: January 18, 2007, 03:48:17 PM »

regardless of what the compression says your gonna need to do rings and valve seals.
your also gonna have to check vallve guides when you take it apart.(they should be fine)


you could have good compression and still get blowby.


so dont be so bent up on checking compression.
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hondarider95
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« Reply #22 on: January 18, 2007, 04:50:58 PM »

So, I shouldn't waste my time/money testing compression? Should I just go ahead and start the tear down? Gery, why do you think I will need both rings and valve seals? Are valve seals something worth replacing anytime your in an engine? Let me know what you all think.
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« Reply #23 on: January 18, 2007, 04:55:24 PM »

definitely valve seals and rings.
you have to remove the head to replace the piston so go ahead and replace the seals. they are cheap and easy to replace.
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hondarider95
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« Reply #24 on: January 18, 2007, 05:00:33 PM »

What else commonly needs to be replaced on a bike of this age? Valves, valve springs, cam chain?

So forget the compression test?
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