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Super Excited! Got a new (to me) XR400R - 2004

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Picked up a pristine 2004 XR400r today. Here are some pix. The bike has been very well cared for. However, the guy I bought it from rode in Colorado and he jetted the carb for 10k feet elevation. Will that be a problem in Nashville, TN? If it will be, what would the symptoms be? Currently, it's not idling very well but It's been sitting un-touched since Sept of 2016 until today. I am going to clean the carb but don't know if I should change the jets or leave em alone and re-install after cleaning? Suggestions? Thoughts?

 

 

 

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Yes sir. Came with title and tag. Prior owner got it slid through the DMV. I just got back from riding it for the first time other than when I was at his house to buy it. I rode about 10 miles. Either the jetting is wrong, the carb needs cleaned, the aftermarket header/exhaust isn't a good match or a combination of all of the above. It runs great down low but misses at high rpm's and doesn't want to idle. Sounds and pulls great. I'll pull the carb off and see what we have as a starting point. Would a basic carb rebuild kit include stock size jets?

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I bet you'll have to rejet. The carb rebuild kits typically come with only stock jets. Refer to the manual to find what you need.

With the air being thinner in Colorado, your bike is probably now running rich. When you take apart the carb post here the jet size and the guys will help.

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If the PO jetted it for 10k feet, it will be running lean in Nashville, not rich. Its entire exhaust system is aftermarket, so freer flowing than stock. Take a look at the air filter to see if it's also aftermarket and check under the seat to see if the airbox snorkle has been removed. All these add up to determining what the jetting should be.

While you have the carb apart, record the current jet sizes and tell us. As well as needle clip position. See if it still is running the stock A16A needle.

It's not wise to be riding it with 10k jetting in Nashvilles sub 1k elevation.

If it's air filter is aftermarket, you're looking at requiring a jetting of at least 160/60 (main/pilot) for its mods and your elevation.

Edited by Trailryder42
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Thanks for all the replies. Been reading a lot about jetting and my head is spinning. I don't really need the fastest XR in the world but I do want mine to run smooth throughout the powerband and not act like it's hitting a rev-limiter at 1/2 - 3/4 throttle which this one is doing currently.

On that topic...Do these bikes have stock rev-limiters? It literally sounds like it's hitting one at mid RPM levels. I'll pull things apart and take pix as I go and post here for assistance. You guys know far more about the specifics of these bikes than I do and I really appreciate the input already. Looking forward to riding without thinking about keeping the bike running when I stop and w/o hitting what feels like a rev limiter up high.

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I bet it's not the rev limiter you're feeling. It's not getting enough fuel. The 10k jetting that's currently in it is too lean for your elevation. You're going to burn up the engine if you keep riding it that way.

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1 hour ago, TY REX said:

I guess it shows what I know. I figured that if the air is thinner, then the bike needs more air and less fuel.

Almost true, when the air is thinner, the engine needs more air but it's not going to get it, so you have to reduce the amount of fuel to be compatible with what air the engine IS getting. If the engine could get more air, you wouldn't need to reduce the fuel. It's a "more air OR less fuel" situation, not "and".

Edited by Trailryder42
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Okay - Tearing into the carb for my lunch break. Will post back soon w/ jetting and pix.

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Okay - Carb removed and partially apart. Main jet is a 138. small one is a 48.

 

Here are pix...

 

Thoughts? What is the stock jetting on this thing? There is/was a little bit of trash in the low speed jet to I imagine that may have been the idle problem. I want to get the jetting right before putting it back together - Will that cracked piece of plastic that was on top of the main jet hurt anything? Could it have contributed? Thanks in advance.

 

 

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That carb looks filthy so far.

Do you have any kind of shop manual?

Idle problems can be attributed to the pilot jet and/or fuel screw. Usually the fuel screw passage. Don't forget to clean it. People often overlook it. Be very careful not to lose its related parts. There's a spring, small washer and oring in there. DON'T go using compressed air to get them out.

That cracked plastic piece is the slosh baffle. Should pose no problem.

Looks like the backfire flap of the choke plate is intact.

Looks like a UNI air filter, but you need to take it off and see if the filter is mounted on the stock stainless steel cage or a plastic cage. It should be plastic for that filter.

That jetting is definitely too lean.

Check the black tip of the fuel inlet needle that hangs from the float arm. You're looking for a visible ring worn into it, that's bad.

Check/set the float height while you have it apart.

You can use this tutorial for guidance:

 

17 minutes ago, JKTrevecca said:

Oh yeah... Clip is in middle slot on the tapered needle thing.

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That's the stock position, so should be good to go.

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57 minutes ago, JKTrevecca said:

Okay - Carb removed and partially apart. Main jet is a 138. small one is a 48.

 

Holy smokes!  I'm surprised it even ran!  Haha.

As long as you're not in the mountains of TN, I'd throw a 160-165 main (depending on stock or aftermarket air filter, and personal preference), a 60 pilot, and raise the needle 1 position (i.e. clip is 4 down from the top).

I'm in NC, at ~400 ft elevation, I'm running (well....was running...until I recently swapped over to a BSR42 carb) 165 main (I like it better a little on the rich side), 60 pilot, and clip in 4th position from top (seems to run better at part throttle like this).  I'm running an aftermarket filter, and FMF pipe.  And the bike runs GREAT.  Cranks perfect hot or cold.

The plastic piece is a shroud to keep fuel from sloshing around where the main is picking up fuel.  I'd replace it at some point, but I doubt it being cracked like that would noticeably change how it ran.

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Got a 160 and a 58 - They didn't have any 60's.. Hope that is close enough to ride this weekend. Patience isn't a virtue I own.

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