400ex fouling out plugs

[trey88]

Hey, I have a 400ex that has a problem. It keeps fouling out plugs, and won't fire over. Once I clear the gas out, and put a new plug in it, it fires up after turning over a little bit. Gaps are set at .028 by the book. I tried reusing the one in the quad after blowing it out, and rubbing it lightly with some sandpaper to clean it up a little bit, but no dice. A new plug fixed it though. It's not a weekly thing, but the quad did sit for 2 weeks with the gas on, so that didn't help. But it also done it when I rode it daily. Thanks a lot.

[AbnMP13]

List any / all mods to the bike and we'll help you out.

[Honda#4]

Sounds to me that he's to rich. whats your jetting at?

[trey88]

Everything is stock. I had the airbox lid off messing around but I put it back on. It had a sprocket but I took it off for a little more top end. As far as I know the jetting is stock. I'm not the best with working on quads, I work on cars, even though the concept is the same. Would a rejet be in order for a stocker?

Also, it's basically flooding out, you pull the plug and it's black and wet. My guess is a weak spark possibly, or the cold weather recently has threw the air/fuel ratio off?

[hornetgod13]

The colder weather would not make it rich but, would lean it out. It could be that your choke is still on or is stuck.
Is your air filter clean? Over-oiling your filter can cut off airflow and make the quad run rich. Are you at a high altitude?

[dariusld]

Is your quad old?

[beaker1214]

I had this same problem, it was really bad in the winter time when its cold. I ended up putting on a white brothers exhaust and that actually made it a little better surprisingly, but I dunno why when it was stock it had that issue too for a while i was putting a new plug in almost once a month, I would guess that its the jetting for sure.

[hornetgod13]

Adding a hi-flow exhaust or filter would lean out your mixture. Removing your airbox lid is a inexpensive way of to troubleshoot this problem. If your quad runs better with the lid off than your settings are rich. What color is the center of the spark plug just below the electrode. That porcelin area is what you should be looking at. It should be brown or tan colored if your jetting is right. Typically the outside threaded area is black. Don't be fooled by that.
I find it hard to believe that your quad is rich with stock sized jets unless something else is wrong. Are you the original owner. Are you certain it hasn't been rejetted.

[Honda#4]

Maybe his float is stuck?

Hornetgod I don't mean to be rude but could you make your mods list a bit shorter, I think it's alittle on the long side.

[hornetgod13]

Originally posted by Honda#4
Hornetgod I don't mean to be rude but could you make your mods list a bit shorter, I think it's alittle on the long side.

Is this better?

[Honda#4]

Thanks I appreciate it, Mods don't like the long lists that people have so in other words I don't want you to get warned. Hope you understand.

[trey88]

Quad is a 2000 model and I bought it from a guy who usually took care of his stuff. It sat for a while though before I bought it, so it could have some kinks in it. He said he didn't change anything other than the sprocket, but maybe he didn't mention something as simple as jets? It's been rode a lot, but I wouldn't classify it as worn out, everything looks good except the plastic is faded and scratched.

Air filter is semi dirty, but not bad at all. When I first tried to start it, the airbox lid was off. Worked on it, gave up, let my dad look at it and put my airbox lid back on. No help either, put a new plug in it, she fired up.

[hornetgod13]

It could have bad/old gas. How long has the same gas been in the quad?

[trey88]

3 weeks to a month. Oil change was done in early january I think, not a whole lot, MAYBE 10 hours on it since then. I wouldnt think it would be bad gas because it has done it on different tanks of gas, and I fill up at our store with both vehicles and the quad, no problems with the vehicles. My cousin fills his raptor 700 up there too and no problems?

Forgot to add, Im not at a high altitude area. Right smack in the middle of North Carolina so its low. The guy I bought it from lives just a few miles up the road from me.

[NRTHBUSH]

my 06 has the same problem.....except it will eat a spark plug in about hours..

it was runing rich before i did my mods....
fmf power core slip on
k&N airflilter/ removed air box lid.
that seemed to make it run richer and was realy when i started to foul spark plugs.
then i re jeted

170 main
i have a 38 pilot
and my needled is on the second clip

none of this has solved my problems...... im changing my main to a 165 to see if that will help and im hoping to get my hands on a 42 pilot soon......

[AbnMP13]

Take the lid off and ride the snot out of it, if it runs well then we know it's too rich.

[trey88]

Originally posted by AbnMP13
Take the lid off and ride the snot out of it, if it runs well then we know it's too rich.

It runs just as well with the lid or without once it is running. Problem is it just won't start. Once it starts it runs great, with the lid off it might make a tad bit more power, but theres not a major difference between the two.

[zrpilot]

Originally posted by hornetgod13
The colder weather would not make it rich but, would lean it out. It could be that your choke is still on or is stuck.
Is your air filter clean? Over-oiling your filter can cut off airflow and make the quad run rich. Are you at a high altitude?

This is not true! Altitude, air temperature, and humidity are big factors that will affect how an engine will run. Air density increases as air gets colder. This means that there are more oxygen molecules in the same space when the air is cold. When the temperature drops, the engine will run leaner and more fuel will have to be added to compensate. When the air temperature gets warmer, the engine will run richer and less fuel will be needed.

[hornetgod13]

Originally posted by zrpilot
This is not true! Altitude, air temperature, and humidity are big factors that will affect how an engine will run. Air density increases as air gets colder. This means that there are more oxygen molecules in the same space when the air is cold. When the temperature drops, the engine will run leaner and more fuel will have to be added to compensate. When the air temperature gets warmer, the engine will run richer and less fuel will be needed.

ZRPILOT,
Read my post again. I was right. I said colder temperatures WOULD NOT make it rich. I never said it would make it richer. I went on to explain that in fact would make it leaner. Did you actually read what I posted?

[AbnMP13]

Go to a 42 pilot jet.


How to change a pilot (http://www.exriders.com/vbb/showthread.php?s=&threadid=221742&highlight=pilot)

[zrpilot]

Originally posted by hornetgod13
ZRPILOT,
Read my post again. I was right. I said colder temperatures WOULD NOT make it rich. I never said it would make it richer. I went on to explain that in fact would make it leaner. Did you actually read what I posted?

I guess not, sorry. I have seen too many people NOT compensate their jetting for temperature and wonder why their quad runs like sh^&.

[wcbomb]

all 400's are cold natured from the factory, but seems they all start a littel diffarent, its very easy to foul a plug on the ex. might go the local shop and get the iridium spark plug for it ,they do work wonders for start ups and last longer too. only downfall is the price $12-15 dollars.