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Old 03-31-2010, 07:19 PM   #1 (permalink)
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400ex won't stay running

Alright guys, bought this quad a couple of days ago for my cousin and I'm working on it now. The guy said it wouldn't stay running, and it had been sitting for about a year. I figured bad gas/dirty carb. So I went and cleaned the carb the best I could, (the inside looks really clean) emptied the gas and put brand new in it.

It has the white brothers pipe, K&N air filter with no lid, 155 main, 42 pilot, brand new spark plug.

I can get it started by giving it some gas, but it won't idle when I let off the throttle. Starts back up just fine as long as I'm barely on that gas, or revving. Now it does have a twist throttle mod. I'm relatively new to quads, I have a yamaha raptor myself. I can get around the basic mechanics just fine, but I'm stuck and its late out so I can't run it.

Do you guys have any ideas what it could be, or some things I could look at? Again it fires right up, I can ride it fine, it's really strong, just when it gets down to idle, it dies.
Thanks.
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Old 03-31-2010, 07:32 PM   #2 (permalink)
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Will it idle with the idle screw turned up a little, without idling too fast? If not you probably missed something when you cleaned the carb. It's easy to miss something.
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Old 03-31-2010, 07:44 PM   #3 (permalink)
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Before I tore it apart to clean, I did have it idling with it up really high, but it was pretty darn fast. Way too fast for an idle. Now also, I've never cleaned a carb so I wasn't sure how exactly to go about it, but everything on the inside really looks pretty clean as far as my amateur eye could tell.
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Old 03-31-2010, 07:53 PM   #4 (permalink)
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If you had to turn the idle screw way up to get it to idle and then it idled too fast, you probably have some debris in your idle circuit. It would be a good ideal to clean the whole carb while it's off.

Did you take the jets out and run a small wire or torch tip cleaners through your jets? You also need to run something through the passages in the carb body to make sure they're not stopped up. If you use a small diameter wire for this, make sure you choose a wire that won't break off inside the carb passages. If you have problems getting the passages or jets unclogged, then you will need to completely disassemble the carb and soak it in some carb cleaner. You can buy the carb cleaner in a can to soak the carb in at your local auto parts store. If you go this route, you will need to remove any rubber seals, O-rings, parts, etc., because the carb cleaner will eat them up.
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Most 4-wheeler problems are caused by a loose nut connecting the handlebars and the seat!!

You only need two tools in life -- WD-40 and duct tape. If it doesn't move and should, use the WD-40. If it shouldn't move and does, use the duct tape.

Last edited by Helmut; 03-31-2010 at 07:56 PM.
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Old 03-31-2010, 09:05 PM   #5 (permalink)
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I didn't take the jets out, I just turned on the choke so it opened up the flap and really sprayed a buttload of carb cleaner down in there. I'll take it off the bike again tomorrow and clean it way better. I'll have to look at the store then for some "torch tip cleaners" I guess?? Thanks for the help guys. Like I said I haven't messed with carbs too much so I don't know a lot about them.

I just realized maybe my pilot is clogged? This is just me thinking outloud but theoretically if my pilot was clogged and nasty the bike would only run when I throttle to about an 1/8 or more, which is what I'm doing...does this theory have any relevance at all???

Also, can you guys help me locate a carb diagram or tell me how many o-rings there are so I can just soak the whole thing??

THANKS!!!!!

Last edited by jgoeden; 03-31-2010 at 09:09 PM.
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Old 03-31-2010, 09:22 PM   #6 (permalink)
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Yeah, you probably need to take the carb off and clean it better. It says that cleaning the carb fuel and air passages with a piece of wire will damage it, but that's usually how I do it and I've never damaged one. It would be better to use air if you can, though, but you'll probably need one of those rubber tipped air nozzles.

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You only need two tools in life -- WD-40 and duct tape. If it doesn't move and should, use the WD-40. If it shouldn't move and does, use the duct tape.

Last edited by Helmut; 03-31-2010 at 09:24 PM.
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Old 04-01-2010, 06:16 AM   #7 (permalink)
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Thanks for those diagrams, that should help a lot!
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Old 04-01-2010, 06:27 AM   #8 (permalink)
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Quote:
Originally Posted by jgoeden View Post
Thanks for those diagrams, that should help a lot!
You are right about the clogged jet, that makes perfect sense of why it won't idle.
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Old 04-02-2010, 03:00 PM   #9 (permalink)
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Ok so I went in and cleaned the carb again as best I could and also soaked the pilot jet and cleaned it. Looked a little better. I also went from a 142(?) to a 155 main jet. I seemed to almost idle, even with the idle screw turned all the way up. So it helped but now I'm wondering if my pilot is too small Its the stock 42, so I'm thinking a 45 might help? Also when I WOT the bike it gave dark smoke from the pipe and killed the engine. I'm thinking way too rich, so I'm gonna try a 150 pilot? What do you think? Also the air fuel mixture screw is 3.5 turns out, is that a little much?

Oh yeah, when I put the choke on the first notch, it seemed to be idling nearly perfect. Wonder if this means I should be changing the air fuel mixture screw at all.

Sorry I'm still new to carbs and properly jetting them, it's a new world to me. Any help is GREATLY appreciated!!
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Old 04-02-2010, 09:08 PM   #10 (permalink)
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You need a bigger pilot smaller than the 155 main and only 2 and a quarter turns out on fuel screw.
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