Need help from Ex Experts

[00Banshee]

My brother's 400ex has a WB E-Series pipe and silencer, WB rev box, 6 holes drilled in airbox lid, K&N filter and outerwear. Everything else is stock including the jetting. He is running NGK DPR8Z plugs. The problem is after about 4-6 hours of riding the plug color is solid black (dry) as far down the insulator as I can see and the quad misses and backfires until the plug is changed, then it runs perfectly again. Is never smokes at all, although between the discs on the silencer there seems to be some black carbon build up.

My question is what is causing the plug to foul out like this so soon. Is it the jetting? I know if my Banshee plugs were this color it would be running rich. Any help would be appreciated.

Thanks guys...

00Banshee

[phatswinn]

he needs to rejet, try buying jets from 1 up to abut4 up and try them all for the best results

[Rastus]

Sounds like its running lean. Like phatswinn said, try going up gradually and keep on testing. When your done, you'll thank yourself for that work.

[bama400ex]

if it was running lean the plug would be white, not black.it really needs to be jetted up with all the mods you listed.

When ever you go with even a pipe you need to jet it. bama400ex is right all of those mods you need to jet it. You got the air fuel mixture messed up jet it it will be fine.

[Kadafiy]

With what you listed it sounds like you're running rich. My question is with all those mods how could you be running rich with the stock jetting???

Four stroke motors plugs should be a white color when runing right. We are not talking about a two stroke. I'm 42 years old I have been around.

[nakomis0]

Coffee brown = perfect, 2 or 4 strokes.

[RAPTORAZ]

Sounds like it is running VERY rich. Which it should not be if he is still running the stock jetting. I'd check the air filter before I did anything else. If it's clean, try pulling off the airbox lid. That should lean it out a little more. What elevation are you at?

[00Banshee]

Originally posted by RAPTORAZ
Sounds like it is running VERY rich. Which it should not be if he is still running the stock jetting. I'd check the air filter before I did anything else. If it's clean, try pulling off the airbox lid. That should lean it out a little more. What elevation are you at?

Hey RAPTORAZ, I agree that it seems to be running rich, (because of plug color) I am just not sure how or why. Am I correct in assuming the plug should be tan in color after doing a WOT plug check if it is jetted properly? I am at about 2000' elevation.

I know on 2 strokes that
WHITE = LEAN
TAN = RIGHT ON
BLACK = RICH

Is it the same with 4 strokes? I see in the replys I have got that some say I am lean and some say I am rich. What are the stock jet sizes for a 400ex? main, pilot, and needle setting?

Thanks everyone for replying. But I am still just as confused because of the differences in opinions.

[cdalejef]

It is jetted too lean for the mods you have made. Over time the lean jetting has caused premature wear on the piston rings. Oil is getting past the rings and causing the plug to turn black and foul out. The top end needs to be rebuilt and the carb needs to be jetted for all the mods you have done.

[00Banshee]

Originally posted by Jeff@QuadShop
It is jetted too lean for the mods you have made. Over time the lean jetting has caused premature wear on the piston rings. Oil is getting past the rings and causing the plug to turn black and foul out. The top end needs to be rebuilt and the carb needs to be jetted for all the mods you have done.

Jeff, Can I do a compression check to see if the top end is bad? What should the compression be? It is still on the stock bore.

[cdalejef]

Ya, a compression test will tell you if it needs to be rebuilt. I'm not sure what the compression is supposed to be right now. I can look it up for you tomorrow when I get to work, unless someone beats me too it!

[00Banshee]

Originally posted by Jeff@QuadShop
Ya, a compression test will tell you if it needs to be rebuilt. I'm not sure what the compression is supposed to be right now. I can look it up for you tomorrow when I get to work, unless someone beats me too it!

Thank You. I would really appreciate that.

[Rastus]

Its running lean, definately.jeff is right, prob overheated and fried it.

I think it must be running rich. If it was oil fouled, the bike would smoke alot. I have a friend who's 400 EX smokes blue some but it never fouls the plug.

Check the jets in your carb just to be sure what's in there. Maybe someone else messed with it before your brother got it.

your brothers 400 is running lean, you increased the air intake, but not the fuel go up on the jet sizes

[Wheelie]

If the quad isn't smoking, it's running too rich.

The stock jets for a 400 are: 38pj, 148mj.

[papaw]

i think stockers hsould be around 125 psi.but i could b wrong...

[TRFOXX]

I would say that its running rich. I have a FMF powercore4 with it jetted at 152 main, 40 pilot, Uni filter with 4 uni vents in the air box. I had only 4 but the plug was still black. I put 2 more holes in the lid and its at the right color now. I did test it without the lid on the last time I rode with a new plug and when I checked it was white. So I put the lid back on and went with total of 6 holes in the lid and that seems to be working. Remember if you mod your air box you need to rejett your main, or vice versa you mod the carb, you need to mod your airbox. You increase the main jet you need to increase more air.