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XR 400 Lack of low end power

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I recently acquired a 2000 XR400 and on the initial ride noticed it didn't have much low end power. The snorkel has been removed and someone has cut part of the baffle/spark arrestor off ( see pic). I've taken the carb off to inspect,it has a 162 main and a 55 pilot,mixture screw is 2 1/2 turns out and float level is correct. Pulled the header pipe off and the welds look untouched. I had one of these bikes about 10 years ago and remember it pulling a lot harder off the bottom than this one,and it was a stock bike!

Is there any thing else I should be checking?

 

20181130_182159.jpg

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What is the air filter like? Stock filter over the stock screened frame or some aftermarket piece?

What's your elevation? If you're at sea level, that 55 pilot may be too lean.

Have you checked the what needle it has in it and it's clip position?

Has the piston/rings ever been replaced? Any idea of how much time/miles on it? Do a compression test.

Does it still have the stock header?

The more you open up the exhaust, the less low end torque you'll have.

I don't know about the UK, but that baffle is not a 400s piece, at least in the US.

Edited by Trailryder42
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Thanks for the replies guys.

The air filter is stock foam and the screen looks stock.

I'm pretty close to sea level. The needle is stock and the clip is in the 3rd groove from the top.

I don't know any history of any ring change etc. was thinking of getting a compression test done,so that will probably be my next move.

The header is stock and the welding build up is still there. I thought it might be something to do with the baffle being hacked at,which is why I posted the pic.

The gearing is stock atm.

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Removing the spark arrester gave my XR400 a big boost in low end power. When I had that bike I remember thinking it must have been jetted from the factory to run without that corking device.

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Grind out the excess weld in the header pipes close to the head. I have done this on several xr's . your previous xr may have had this done. It will get you a lot more low end by getting the exhaust gas out of the cylinder so that incoming clean/fuel air burns a lot better. somebody may say that if you grind out the weld the pipe will fall apart. bullshit. you don't need  or want any restriction at that point. as a retired welder I have a pretty good idea of how much weld is required there and it isn't much. 

when I bought my xr400 it had an after market muffler and it was weak every where. cleaned it out and it was strong everywhere.

good luck.

Edited by Robert Branson
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Opening up the muffler gives more bottom end.  Some restriction , to a point , gives more top end. Try it both ways in first or second gear , and you'll see by where it lifts the front wheel.  

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I don't see where anyone mentioned valve adjustment. Many people don't think about valve adjustment as long as the bike starts and goes.

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I did check the valve clearances,all were in spec,forgot to mention in my original post.

I'm going to get a leak test done and see what happens there,I'll post back my findings.

Thanks for all your help guys.

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Gear it. I used to run a 14t and 50t combo on my stock bore 97 with a uni filter and 4" supertrapp. 

Now I have the niche 440 big bore (very happy with it and possibly the best $70 I've spent on a bike) and am running a 15t and 50t. Been playing with jetting a bit and put a quietcore 3" supertrapp on it. Pretty happy with it for a trail bike. Tops out at 72mph but can effortlessly pop the front end up in 3rd and can clutch it up in 4th and 5th. 

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I've had the leak down test and not much leakage coming out so motor seems ok.

Just ordered a tail pipe insert which I will try and I have a 14 tooth sprocket which I may put on.

Still not sure about the header pipe,seems to be conflicting views on weather to open it up or not.

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13 minutes ago, pappa_t said:

 

Still not sure about the header pipe,seems to be conflicting views on weather to open it up or not.

That's why I said to try it yourself and you'll see I'm correct. It's not a lot , but it's noticeable. Like I said before ,  compare both ways  and where in the rev range it lifts the front wheel in a lower gear.

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