07 400ex

[maddawg400ex]

A little while ago i bought a 2007 400ex, it ran completely fine. I had it sitting a while cuz i never had much time to work with it. For about a month the atv would ride just fine no problems. after a little while i noticed that it would start up but then would die. I didnt have much time to mess with it so i just left it alone. Soon enough it would just quit starting up. It cranks but does not fire. The battery checked low so i jump started it with a car. it turned over just fine but no fire. I also checked for spark, there is spark but may seem a little weak. not really sure what the spark is supposed to be like. the fuel is good, drained old and put new in. I fully charged the battery but still no fire. I was told that i may have damaged something while jump starting because of the amperage that was going through the atv due to the vehicle. Also was told that it may be the coil. The coil is receiving signal. I measured the volts on the secondary coil ( the one thats grounded) and it alterated from 12v to 0. It seems like there is proper signal. not sure if maybe the coil is not producing high enough voltage for a proper spark. the spark plug was wet when i pulled it out so it seems like it has fuel coming in. Also replaced the spark plug, still nothing. Not really sure where to go from here.

[DragonGunner]

Wet plug,....engine won't start
1. flooded
2. throttle valve open
3. dirty air filter
4. improper adjusted pilot screw.....clean carb with carb cleaner, complete tear down, you may have tarnished gas plugging things up.


Weak or no spark
1. plug
2. loose wires
3. shorted plug wire
4. ignition coil
5. pulse generater
6. exciter coil
7. bad engine stop switch
8. ignition switch
9. bad ICM

My guess you got old tarnished gas plugging up stuff in your carb, carb cleaner an tear down is first thing I would do....try taking airbox lid off, lets more air in....if starts with lid off, then you need to clean filter.

[maddawg400ex]

the atv ran just fine a little while ago, its just been sitting in the garage. I can't imagine how it could have flooded.

i took the carburetor off but didnt take it apart too much, looked kinda clean but i could be wrong.

the air filter was dirty but i removed the filter completely when i tried to start it, nothin really changed.

how could i properly adjust the pilot screw? just by cleaning out the carbr or tuning it? the atv ran just fine so is it still possible there is tarnished gas clogging the carb?

I will look more into the wires. not sure how to properly check the coils either.

[kt1148]

When I stored mine the first winter, I had it in the metal shed, no insulation or heat. Didn't ride it or fire it up for at least three months. I finally pulled it out to fire it up and it soaked the plug because the float in the carb was stuck in the down position. I picked up the back of the quad and dropped it a few times and it released finally. just a suggestion...

[maddawg400ex]

I tried dropping it a few times, quite a few times actually and nothing really changed. I was working with my brother and he noticed a spark one time when i tried starting it. I checked the fuse and it looked broken, not sure if that was what caused the spark but it sure seems like it. I really dont know where to go from here.

[CJM]

Change the fuse then.

Have you tried push starting it?

[maddawg400ex]

yea i had the fused changed, didnt change anything. The other day i tried starting it and it fired perfectly, ran just fine and everything. i killed it because it was a little late and i didnt want to bother the neighbors. Then it started acting up all over again, turned but no fire.
today i try starting it and it starts but takes a little while with the starter. It drives just fine. The problem now is when u hit higher rpm's there is huge backfire and the atv dies. after that it just turns and no fire. i pushed started it using a truck and it took a while to get it firing again. after push starting it the atv runs perfect again. sounds as if there is nothing wrong. as soon as i hit high rpm it back fires and the same thing all over again.
the atv will start just right if i dont kill it with the high rpms. after i hit high rpms it will not start up with electric start, only push start.
my friend also noticed that after i hit high rpms and kill it, there sometimes is some spark coming from the back of the atv when i try starting it. fuses are fine and again runs perfect after push start.

[CJM]

It sound slike a bad connection somewhere. Check all grounds and wiring connections-specially the starter.

[maddawg400ex]

i checked most of the grounds, i guess i still have a few more to find. I dont understand how that could affect the atv at high rpms. it has huge backfire and then dies. works fine otherwise.

[CJM]

Could be a loss of spark.

The problem with the post is I cant physically see wtf is going on, its tough to sort out.

Since it was running fine before it makes me wonder wtf is going on.

I wonder if its timing related. You ever checked the valves?

Check the following items to be sure they are in good working order;
-All electrical connections and wiring
-Carb, jetting, clean carb
-Air leaks at carb/motor
-Valves, timing chain, cam
-Plug, is it bad, good or whatever. Cracked insulator, etc.

Thats what I would check.

[maddawg400ex]

yea i guess its hard to tell without seeing it.

not sure how to check valves, kinda scares me to open it up with how many problems its already giving me.

I will continue to check all the connection and wiring, it just confuses me a bit cuz it looks like a mess.

I hear alot of people saying they think its my carb, like theres some needles or something that might not b adjusting properly. I really dont know enough about them to say if thats whats causing the backfiring at high rpm and then killing it. funny thing the electric start dont work right afterwards, confuses the crap out of me.

for the loss of spark could that be coil too? i couldnt find how to properly check those things. i know theres signal going through but thats all. not sure if the plug wires or coil have proper resistance or whatever.

if it would leak air somehow would that have something to do with it killing the atv? it seems like it should only limit the power or something.

[CJM]

http://www.atvriders.com/articles/valveadjustment400ex.html this is how to check and adjust the valves.

Im no good at measuring the electronics, pm member DnB he knows exactly how to check the coil and whatnot.

[maddawg400ex]

Tried to pm member DnB and still no reply. Been messing around with the atv starting it and checking when it dies. After a while it just started to run more smoothly with only a little bit of backfire, but it kept running. I decided to take it out and test it. When I was pulling it out of the garage I noticed there was 'dirty water' underneath. it was all snowed up outside so i just assumed it to be water in the garage. After taking it around a few blocks it began almost pouring this 'dirty water' and sure enough it was oil. I killed it immediately and pushed it back home. checked oil level and there was nothing. I google symptoms of leaking head gasket and found almost the same problems I was having. I'm almost positive that its some sort of gasket. There was a bunch of black residue along with the oil that leaked all around in the area of the shift pedal. i took some pics, hope maybe someone can help me identify if it really is a gasket and which one.

[maddawg400ex]

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[maddawg400ex]

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[maddawg400ex]

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[maddawg400ex]

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[DragonGunner]

Shift fork seal....shouldn't be a problem with it running though...if you were too low on oil there is a sensor that will shut off the engine in that area though. Also looks like the chain may off come off sometimes and damaged the case and its leaking there also.....just gotta clean and run and see.

[slightlybent47]

Originally posted by CJM
It sound slike a bad connection somewhere. Check all grounds and wiring connections-specially the starter.

Agreed^
There is a bundle of wire connectors rapped in a rubber covering. These wire plugs with the rubber shield over them sometimes get loose. Check them and make sure there plugged all the way in. sometimes when they get loose the rubber covering will let them touch and it will run fine, then they will break the connection and shut the bike off.
They may look like there plugged in, but check them anyway.

Does it have a tether switch? These can get dirty and keep it from running.
Most turn the bike off by the key switch, and not the tether.
Also work the kill switch back and forth, dirt gets in and sometimes they get stuck as well.

Also there is a relay down by your shifter on the left side, they need cleaning from time to time as well.
A little dust or dirt can make the switches not work properly. Blow them out with air and use a little w-d on them.

[dougie400ex]

my friend's 2003 400ex had this problem and it was a bad connection for the neutral light. It really surprised me when i figured it out.

[maddawg400ex]

Is it possible that the oil sensor switch was what wouldnt let me start? I first started it by push start, so maybe that bypassed the sensor since i didnt use electric start?

I think I lost all the oil through the case. It looks as if the gasket is a little out in one area and then comes what looks like a crack in the case. How would i fix this? Could I just use RTV to reseal the case and also use it to fix the crack?

[AtvKid4Eva]

The correct way to check the oil on the 400 is to let it idle to normal temperature shut it off and then check it. If you dont let it run, you will get a false ready making it appear to be empty. If you lost 2qts of oil, you would have a huge puddle under the bike. Try to push start it, if it starts let it run for a bit and then shut it off and check the oil. Unless you have a huge puddle under the bike, i doubt you lost all the oil.

[AtvKid4Eva]

Originally posted by maddawg400ex
Is it possible that the oil sensor switch was what wouldnt let me start? I first started it by push start, so maybe that bypassed the sensor since i didnt use electric start?

I think I lost all the oil through the case. It looks as if the gasket is a little out in one area and then comes what looks like a crack in the case. How would i fix this? Could I just use RTV to reseal the case and also use it to fix the crack?

it also looks like either you or the previous owner had the chain come off and it cracked the case. It kind of looks like someone attempted to fix it at one time. Regradless im sure this isnt why the bike wont run right. A 400ex will run even with no oil haha

[maddawg400ex]

there was quite a bit of oil spilled out on the street, not sure how much because i noticed it would spill at random. ever since i bought it its been causing me headaches, just recently discovered that the case was cracked. im not sure what the previous onwner did with it but its a little beat up all around. im probably gonna start with fixing the oil leak problem. What would be the best way to fix the case? If i take it off im assuming that i would most likely need to make another gasket too.

[CJM]

Looking at that case the previous idiot of an owner did the following:
1. Chain was to much slack or had a bad master link
2. Threw chain off
3. Smacked case
4. Screamed OH FUDGE!
5. Decided to JB weld and what appears to be RTV on the case

Id say your first step is to clean up as much of that as possible. If you cant clean it enough with brake clean use aluminum etching wheel cleaner like eagle1.

Once you can see the damage you can see if its even worth fixing. Id say it doesnt look promising as part of the case appears more gray than the rest which Id say is likely JB weld. The orange stuff sticking out of the case seam is high temp orange RTV silicone.

So if the case is indeed busted you can:
1. New case
2. Tig weld case
3. New bottom end/whole engine.