How to tell if a 400ex is over heating?

[bigbuck90]

I just bought a cherry 2000 400ex 2 days ago.When i got it it never smoked or any thing in that nature.Well today i took it out,and i was in the woods riding around in first gear bustin a trail.And when i got out of the woods i hoped off real quick, i noticed it was smoking a little bit.So i gave it a little gas and it did even then.I took it down the road in 5th gr at about 1/2 throttle to see if that would help.it did a little bit but when i rev it up and let off it smokes then.Its a blue smoke so its oil,if its the piston and rings and i need to replace them.Should i go stock bore but with a high comp piston with a stage 1 hot cam.Or should i bore it out to a 416 with a hot cam stage 1?thanks

[bigbuck90]

Also i took the baffle out of the stock exhoust with out changing the jetting,could this cause this?

[bigbuck90]

Also i took the baffle out of the stock exhoust with out changing the jetting could this cause this?

[bigbuck90]

any body...i need help :confused:

[gregrob]

Yep, blue smoke is oil.

I would call Colby at CD racing and see what he recommends.

I just did a JE 11:1 416 piston kit and I'm putting a stage 2 hotcam.

Man just the piston alone made a huge difference.

The stock got so hot in the sand one time it started white smoking. The rings were leaking badly and everything was fried, piston, rings.

With the new setup and just jetting it RIPS.
highly recommended.

[JOEX]

Nothing wrong with a 416 bore but there's the option of a 406 bore if the cylinder even needs to be bored. It will depend on what the condition of the cylinder is. There are a few measurments that will need to be taken, usually by the machine shop if you're not familiar on how the do them. Out of roundness and taper are a couple...

Givin it's a 2000, depending on how it has been maintained and used, it's likely a fresh bore is the way to go.

Valve seals should be replaced as well and the other components of the valve train should be inspected too.

I'm not real familiar with how the baffle affects jetting but it could be possible the mixture went lean after removing it and accelerated the already borderline wear on the motor.

[romeo_1885]

i put a stock bore with a higher compression piston on my 05 with a stage 2 cam and it rips, i mean no beginner could hold on, but i have a few more mods that make it faster... the stock bore piston is a good idea as long as your cylinder walls are in good shape... when you change the cam be sure to adjust your valves as well

You took the spark arrestor out not baffle. If you want to know what the baffle is its the wall that blocks off lots of air flow. If you look inside the muffler you will be looking at the baffle. Some people drill a 1" hole in the baffle and it helps some for power and makes it a little louder. Removing a spark arrestor does not increase air flow enough to mess the jetting up, its about good as a mod as changing to a aftermarket filter if that.

Does it smoke on start up? If it does then you have valve problems. If it don't smoke on start up then your valves are probably fine.

It needs piston rings for sure. If you put different rings on the piston it would probably stop the smoking and give better compression. But if you have enough money this is teh perfect time to put a big bore in it.


And you cant really tell if a 400ex is over heating. Only way to tell is if you get a aftermarket oil dip stick that tells you how hot your oil is. Factory affects sells heat temp stickers that sell for around $10 for a set of 3. Not sure how good they work but it would be a good idea to put one on the oil tank so you know how hot you are. When my 400ex gets to hot it tends to stall and be hard to start. But if oil reads over 200 degrees I think the motor should be shut off so it can cool down. Also a aftermarket muffler helps it run a little cooler by letting the hot exhaust get out faster.

[bigbuck90]

Update...Today i was riding it and it was running great.But i had some one else rid it so i could watch to see how bad its smoking.The only time it smokes is when,u rev it up to almost wear u need to shift.And let off the gas and let it idle down by its self.So im guessing that its the piston and rings.Its smoke's pretty good,when your letting off the gas but it wont smoke when your on to it.Also could it be the oil thats in it?Im asking this because i dont no what the origional owner put in it,but i think the tranny is slipping a little bit.Not a lot,but just enouph to tell for like 1-2 seconds then it stops.I heard that the wrong oil could cause this,and if it could cause that could it cause it to smoke?If i need new rings and a piston,Would a 416 bore with a stage2 hot and a slip on be a good set up?I want the comp to be 10:2.5 i beleive.Sorry for all the questions,this is my first 400ex im used to banshee's...

[bigbuck90]

I also dont want to deal with the hd studs and cam chain,would this set up be good for that?

[hondaman954]

Hi smoking on decelerating or letting off the gas is a deffinate Valve seal leaking. High intake vacume causes the oil to be sucked passed the worn valve seals. On acceleratin the intake vacume is lower so its not pulling enough oil past the seals to notice it buring out the exhaust. My opinion is change the oil and filter with a good quality 20w50.

Only way I could see the problume being the oil is if it was thin as water so its not the oil. I used to kind of like the smoke coming out of mine but I new it was robbing my power so I had mine fixed. If you go fast like 3rd gear and rev it out then let off the throttle all the way and down shift to 2nd it should blow lots a smoke :devil: Mine used to smoke up the whole yard.

If I were you I would go for 440 kit. I think the head stud pulling issue is dealing with high comp pistons not how high cc you go. 10:2.5 would be fine.

[400exrider707]

It is burning oil, that is for sure. Here is what I would recommend for a rebuild

11:1 piston for reliability and pump gas any JE or a wiseco, and whatever bore size you may need. A 406 would be great, but if you want to go bigger it shouldn't cost any more.

CRF cam chain for the utmost reliability. The stockers tend to stretch and that causes many bad problems. The CRF is basically a heavy duty chain at a fraction of the cost of a stock 400ex one. $25ish from servicehonda

A cam if you so choose, while you have it apart

valve seals, and get good ones, not cheap ones.

This should fix your oil burning problems and give you a good power boost, while upping the reliability.:cool:

A cheep cam that adds power is a stock xr400 cam.
A stock 400ex cam is a low end cam. The xr cam is more of a mid-top end cam. So a stock xr cam is about good as a stage 1 hot cam.

[JBDIV]

I won't out of hand disagree with what has been said thus far... But, I also believe in the K.I.S.S. approach. The first thing I would do is check the valve adjustments and inspect the seals. After or better both, I would do a leak down test. You can by a leak down test kit from an automotive supply store pretty cheaply. If during the test, you see bubles around the valves (apply a little oil with an oil dispenser around the valve seats) you know your valves need reworking. IF they don't leak but you loose compression you know it's the rings. Good luck!

[bigbuck90]

any body else have more suggestions?