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Cleaned carb, put back together and is now spluttering


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I've just got an xr 400, and thought I'd give it a service. So I cleaned the carb and blew through all the jets, breathers etc. I then put it back together and tried to start it, and it is an absolute bitch to start, when it eventually does start you have to rev the bike up otherwise it will stall and not tick over ( when I rev it up it back fires and pops quite a bit ).

What the hell have I done? The only thing I can think of, is the little white thing fell out when I opened the carb up, so I checked a Haynes manual and put it back in as it says. But maybe it was setup differently.

Any ideas?

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If you had the intake manifold off, make sure the o-ring between it and the head is there and in good shape.

Could you have knocked the float height settings off while you were cleaning it? Did you check them before putting it back together? Minimum drop should be 14.5mm and max drop should be 19mm, using the technique described in the manual.

Are you using the choke properly? Up is on, down is off, middle is...............mid.

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I didn't take the manifold off. But I did clean out a bit of sludge stuff that was at the bottom bowl of the carb, so maybe I loosened some of it off and it then got jammed in the pilot jet.

I'm pretty sure all the bits went back in the carb, is it worth taking the mixture screw out, and re-installing it?

I don't really know much about adjusting the mixture, so I normally don't touch it as I dont want to cock it up. I know its 1 1/2 turns from lightly seated, but then, what if doesn't run properly? how do you know which way to turn for what?

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Yes, God Da* it George, swear!

If the carb was mucked up enough when you bought it to need a cleaning, then yes, the fuel screw and passage should be done too. It is what regulates the flow coming from the pilot jet. It is what regulates the fuel mix at idle and for starting.

IN(clockwise) is leaner(less fuel) and OUT is richer. 2 turns out is the desired sweet spot, but depending on what your elevation and pilot jet size are, anywhere from 1.5 to 2.5 turns out is the recommended range to try to tune it into.

The PO may not even have had it jetted properly. Post what the current jet sizes in it are, your elevation and any intake/exhaust mods if any so we can see if you're even running the proper jetting in the first place.

I'm pretty sure all the bits went back in the carb, is it worth taking the mixture screw out, and re-installing it?

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If your carb is clogged and you clean it and then it still does not start, for me at least, 9 times out of 10 cleaning it again fixes the issue. Sometimes it takes more than twice if you are not totally thorough. Sometimes it can take cans of cleaner to get it where it needs to be. Are you using compressed air? That can make the difference. Also make sure the o-rings don't have any tiny cracks in them. Don't be afraid to fix things twice(or more), it's way better than sitting around wondering what could be wrong.

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Another thought. If you are new to the xr400 they can be nuts to start if you do not know the method(methods). You could kick it all day long, and not get a thing. There are plenty of good posts on it if you think that may be an issue. Good luck

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