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2004 Xr400/440 build.

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Hi everyone, I am doing a build up on a 2004 400 for a mate. He bought this bike about a year ago and then cleverly ran it dry so he cooked the top end.

He asked me to rebuild it for him and his exact words were "I want it to be SIK", "Build me an animal bike". I suggested buying a CR250 or similar and selling the XR to a wrecker but he insisted on doing this thing up. He wanted a big bore kit and all the goodies and even asked how it would compare to my 93 XR630. I think the 400 will be quite a bit more everywhere than the 600.

So far I have done/bought the following.

1mm oversize valves with Ti retainers and kibble white springs and new guides.

Stage 3 hot cam.

New 440 cylinder kit with a 10.5:1 Je piston.

Hotrods Conrod.

The head is still in the shop getting the valve guides installed and seats cut for the oversize valves.

I will blend the ports to suit once I get all that back.

Now I realise that there are more aggresive cams out there and a higher comp piston available but I have decided to tone down the specs a little because such a bike will be very high mantinence for the owner to handle let alone his riding ability. So I doubt it will live long in this state of tune. Anyway I mainly took it on because a, I think it will be a fun build and b, I wanna see how it will go. I own a 93 XR600r with a 630 kit and would love to see how they compare.

It took 8 hours to drill the swing arm bolt out and a lot of "don't do it mate" to keep me from sending the bike over a cliff but we finally got it out.

I still have to send the crank to the shop to get the rod, pin and bearing changed over.

We will be ordering an aftermarket carb to suit very soon and new bearings for the rest of the motor/gearbox. Any advice on what's the best carb? He keeps telling me "pumper carb, get me a pumper carb".

I also read that I might need to clearance some areas in the case for the piston. Are there any threads in here of such a build up. All I seem to find is a lot of threads with questions where to get the kits but none on the actual builds so I thought I'd start this one and post pics and get advice at the same time. I have also read that the general opinion is to keep away from the 440 kit and just do the 426 or 416 kit. Well it's a bit late for that now so this will be a 440 thread and I hope to find and share as much info as possible on the subject.

Feel free to post your info, pics and advice.

Also I thought I might add that I compare every other bike to my XR600r. We go riding every week end and it's quite common for us to swap bikes especialy if someone had done something to theirs so we can all sit around and shit talk about it at the end of the day. I used to have an 80 YZ465 and I once compared everything to that but that was 15 years ago and one I regret selling.

We live in the desert in the middle of Australia so the riding terrain varries from trails to flatout cross country to rally style racing on dirt roads to motocross and jumps. But more on that later.


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Hi George, I built mine to 426cc because I did not want to deal with re-sleeving the cylinder. Baja Trail Rider has a couple of 440's and has said that you do not have to do any clearance modifications to the 400's but you do need to do them on the XR250 to 300 overbore.

I think you have made some excellent choices for the piston and compression. :smirk:

I would however recommend a larger carb to feed the beast! Personally, I'm using a Mikuni BRS42 (from ebay, for a Polaris 500). I find that the 42mm carb opens up the entire RPM range. I have ridden on pumper carbs but find the 42mm just offers more grunt.


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This the carb?

As for sleeving. It worked out cheaper and a big time saver to just buy the kit so we went 440.

Yes, that is the correct carb.

Check out this thread for a lot of info from others that are running that carb on their 400's. It's kind of a long thread, but there is a TON of great info in it. :smirk:


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