HELP!! "NEW" 400EX fouling plugs

[Youngblood]

Hey fellas, I recently picked up an 05' 400 ex in immaculate condition. She ran like a top when we picked her up but I went to fire her up to putt around the yard, she starts fine with full choke on, switching to half choke and she idles but died after a few minutes, she wont run with the choke 100% off (even when warmed up), a lot of popping and backfiring with the choke 100% off, pulled the plug and the ceramic is dark dark grey as well as the electrode, the "tang" is lighter gray. The bike has a White bros mx4 slip on and K+N filter with a bone stock airbox and intake setup. It was supposedly jetted by the prior owner. do you think I'm running too rich? Like I said it ran 100% when I picked her up with no issues but he did fumble with the idle a bit which I thought was kinda odd. What do you guys suggest for a starting point as for main jets, pilots and needle clip heights? Also I'm in CT @500 ft above sea level, I picked up the qaud in Ohio which is about 950ft above sea level, could this be an issue as well? Thanks

Joe

[Wheelie]

Remove the carb and clean it, also check and document the sizes of each the pilot and main jets and report back here.

[brodzowski]

If it ran perfectly fine before you got it, don't jump into jetting and blame it right away. Do the easy stuff first. Change that plug first, don't clean it, brush it or whatever, go get yourself a brand new plug and take that out of the equation. You'll be able to read it that way too. You have no idea how long this quad sat before you got it last winter either. Make sure the battery has a full charge. Sounds silly, but I've read that battery status can affect spark. Lastly and most importantly, drain the gas that's in it INCLUDING the float bowl at the bottom of the carb and refill it with fresh gas. Both of my motorcycles sat all winter with Stabil in them even and they still got moisture in the gas that I had to drain out. They both did exactly what you're talking about. Once those three easy things are done then see where you're sitting and you'll have a good place to start on jetting if the bike actually needs it.

[hondaking52]

this will usally happin wenever you buy somthing used, the bike is not used to your riding style, thus starts fouling plugs, happend to me with every used thing i've bought, damm 02 kx 85 went thru like 4 plugs!!!!, lol, and my ex went thru 1 or 2.

[Youngblood]

Hey Brodzowski, Iv'e been keeping her on a battery tender since I got her (last weekend) so hopefully the battery is out of the equation (seems to be pretty strong). I'm gonna do exactly all of that first, good call, hopefully she's only just got bad fuel or gummed up carbs like your saying. I'll change the plug, the gas, drain the float bowl, and maybe run some seafoam thru and then see what she does, the guy said theres probably 10-15hrs on the qaud so who the hell knows how old the gas is. If that doesnt do it Wheelie I'll let you know about the pilot and main jet size as well as the needle clip position on the slide so we can try and get this nailed down. Hopefully I can get this set by the weekend to be ready to ride!

Thanks fellas

Joe

[Wheelie]

If you don't know how old the gas is, drain it all out and fill er' up with fresh premium.

[Youngblood]

Alright fellas, heres where we stand as of tonight, I drained all the old fuel, drained the float bowl on the carb, changed the plug with a fresh one, filled her up with fresh 93 and a little seafoam. She fired up with no issues, I let her warm up and rode around my yard, after about 5 mins I could hear a difference in the exhaust note and she started popping and backfiring after I tried to clear her out. Pulled the plug and it still looked damn near brand new, no wetness or dark fouling anywhere. I let her sit for a few minutes and fired her back up, the idle was very irratic, it was kind of surging, it would idle ok for a few seconds then almost die out then it would ramp back up to idle speed until it finally died. Like it was choking or something. That was with the choke 100% off, with the choke in the middle position the idle ramped up signifigently. Ran out of time tonite, but I'm guessing Im gonna have to pull the carbs and see what the hell is what? What do you guys think?

[Wheelie]

Clean the carb.

[hondaking52]

i may be wrong so dont go nuts, but it sounds like ur timing may be out, if it was jets ur plug would be off colored, but i'm not mech so, and clean ur carb.

check the spark plug you might have a plug too cold

[Wheelie]

Originally posted by FlewByU352
check the spark plug you might have a plug too cold

Incorrect. The coldest plug for these is a DPR9Z which wouldn't cause the problems he's describing. The carb needs cleaned, it sounds like the idle circuit is plugged.

[storms400ex]

Originally posted by Wheelie
Clean the carb.

^^^^^^^^^^^ X-2

[Youngblood]

Alright fellas, that would be so friggin sweet if thats all it was, Im running NGK DPR8's for plugs. I'm gonna pull the carbs, drop the float bowl and soak everything down with carb cleaner, any particular way I should go about it, should I pull the pilot jet completely out and then clean it? anything special I should be watching out for? I'll let ya know after I pull the carbs and clean em (hopefully tommorrow after work) how everything went. Thanks again fellas for all the help so far!

Joe

[brodzowski]

I would pull the jets all the way out and clean them yes. It'll probably make it easier to check the size once you do as well. That way if you do have a jetting problem these fellas will have a starting point to work from. Get it good and clean and if it still acts silly you can get some more help then. Be careful putting the jets back in. Don't over tighten them. Just a nice snug.

[Wheelie]

Pull both the pilot and main jet out. Clean each jet with a small wire and carb cleaner. Remove the mixture screw as well and spray carb cleaner through the hole and all corresponding passages.

[richards]

I agree clean the jets. A clogged pilot jet could cause symptoms like you describe.

Also, is there a significant difference in altitude between where the po rode and where you are riding? If so rejetting may be required.

[Youngblood]

Cool, I'm going to get started in a few, I'll pull all jets out and the mixture screw and document the sizes, Richards where I'm at in CT is 500ft above sea level, where he was in Ohio was 900-950ft above sea level. I'll let you fellas know the deal as soon as I can. Thanks

Joe

[richards]

Originally posted by Youngblood
Richards where I'm at in CT is 500ft above sea level, where he was in Ohio was 900-950ft above sea level.

OK that should not make any difference then. If it were a couple thousand feet it could start to affect the jetting.

[kilgoja]

also check the idle speed adjustment

[Youngblood]

I think we got it fellas!! I pulled the carb apart, pulled the pilot and main jets out and soaked them in crab cleaner then, blew them out with compressed air, soaked them again and checked the outlet holes with a small led light to make sure they were free of obstructions. The main jet had a green kind tarnish on it, like it had a little water in the float bowl at some point. I soaked down the inside of the carb body and blew out all the orfices. The main jet was marked 146 on the face and the pilot a 38. I took the main to the local dealer and the lady insisted that it was a mikuni jet, i told her I didnt think so because as I had told her several times it was for a 400EX with a Keihn carb. I looked at the keihn 150 main jet and the opening was a little smaller than the 146 main that was in my carb, I'm guessing it's a dyno jet kit? I put the jets back in snug and turned the pilot screw out to 2.5 turns out. Crossed my fingers and fired her up.....She caught right away, let her warm up enought to turn the choke off 100% and she idled for 10 mins with no issues, I hopped on her and blasted around the yard for about 15 mins with no issues, I tried to get everything from wot to just barely moving. No more backfiring on decel at idle like before. Is set the idle to about 1400 rpm's. I pulled the plug and there was only a little color on the ceramic and it was a very light brown, the electrode was light grey and the "tang" was white. Do I have to ride her a little longer to try and see if any fine tuning is needed? Should I bump up to a 40 pilot jet? Thanks again fellas and I'm thinking the good cleaning was the ticket!

Joe

[dabrowat]

Glad to hear its fixed! I have a similar problem, my plug is a grey ceramic color. When you say you turned the mixture screw 2.5 turns, does it mean u tighten it all the way and screw it out 2.5 full turns or 2.5 half turns?thx

[brodzowski]

Glad to hear you're back up and running. I don't think that I would change jets if it's running good. If you really wanted to dial it in, there is a thread related to setting the mixture and what each part of your carb does. ZRpilot wrote it within the last couple days and it's still up on the first page. READ it. It will solve alot of your questions about what the right tuning is and will also solve the question you asked about whether to bump up the pilot or not. While the community is here to help you, research is your best friend. Happy trails!:macho

[Youngblood]

Thanks again fellas, hey dabrowat, thats 2.5 full turns out when the pilot screw is lightly all the way seated in. Brodzowski, I went fishing around the forum before and found ZR's write up which was great, I'm gonna try and dial the pilot screw in to try and make her tip top. Good lookin out guys!! Take it easy

Joe