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XR400 engine cutting out?

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2003 XR400, not sure why it almost cuts out when the engine gets to a higher rpm. I cleaned the carb twice, installed new jets 45 and a 145. New fuel tank screen. and have adjusted the pilot screw. Starts fine and smoth at idle. Sudden lose of power just before you would shift to second. Do you think adjusting valve clearance might be a fix. When I got the bike it would not start so I have no idea if it ran like this before the carb was cleaned. Thanks for any help...

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That jetting is extremely lean for your elevation(I'm assuming near sea level). It must be completely stock intake and exhaust-wise. If it has any intake mods(snorkle under the seat pulled, aftermarket air filter and cage) or exhaust mods( other than the stock can or a modded stock can), then your jetting IS too lean.

If you haven't checked/set the valve clearances since you've owned it, then yes, do so, but tight clearances usually effect starting, and you said it's starting ok.

Check to see where the clip on the needle is set. Should be in the middle position, 3rd from top.

I don't suppose you checked the float level while you had it apart?

You say you've adjusted the fuel screw. How many turns out from seated do you have it now?

Make sure the carb vent lines are clear/not clogged up.

Post back here with your intake and exhaust configuration.

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Checked float level and it seemed to right near .57 in. Clip is 3rd position, and started with the pilot screw out 2 1/4 then adjusted when running along with the idle screw. I will go out and check the vent lines. It has stock exhaust and the snorkle is gone.

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Tried it with the vent lines off and still the same trouble. will check valve clearance when it cools off.

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What about the air filter? Is it stock? Do you know the difference?

For the exhaust, look down the outlet, between the outer silver trim ring and inner outlet tube. May need a flashlight, but look to see if there have been any holes drilled there. You're looking for the Gordon mod.

If you took the float level measurement properly, using the correct technique as described in the manual, that .57" = right at 14.5mm, so that's good.

So, you started the pilot screw at 2 1/4 out. Where did it end up when you were thru adjusting it?

Do you use the choke to start it? I want to make sure you're positioning of the lever for on/off is not backwards. Off is all the way down, On is all the way up.

Jetting still seems screwy to me, but I'm not suggesting anything til I have these other questions answered.

I need to know from some of you other post Y2K year model 400 guys if the stock pilot is still a 52 for those or not. What about the stock main, is it still a 142?

Checked float level and it seemed to right near .57 in. Clip is 3rd position, and started with the pilot screw out 2 1/4 then adjusted when running along with the idle screw. I will go out and check the vent lines. It has stock exhaust and the snorkle is gone.

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Ok the jets in it were 55 and a 155 bad info to start sorry. Uni air filter and no snorkel. the valve clearance was real close, not the problem. Changed the main jet to a 168 and still had the same problem (higher rpm bog, very very bad) its at about 3/4 throttle. Ran it with the gas cap off, vent lines are clear. None of these things helped. Can anyone think of any other suggestions. thanks

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I have not needed to use the choke to start it, I have pretty much left it in the down position. When the the engine is running it will stall if I put in in the upward position so I think thats fine?

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OK, going from a 155 to a 168 is a huge jump. That's 5 sizes. What might have been lean before may now be too rich with that big of a jump.

Did you look for any holes between the outlet tube and spark arrestor end cap like I described earlier? I ask because if the snorkle has been removed and a UNI filter installed without also doing the Gordon drilling to the spark arrestor, you run into funny and difficult jetting issues trying to get the bike to run right. More airflow thru the intake, carb and engine means you have to allow more flow thru the exhaust or you end up with a bottleneck.

What's your elevation?

Ok the jets in it were 55 and a 155 bad info to start sorry. Uni air filter and no snorkel. the valve clearance was real close, not the problem. Changed the main jet to a 168 and still had the same problem (higher rpm bog, very very bad) its at about 3/4 throttle. Ran it with the gas cap off, vent lines are clear. None of these things helped. Can anyone think of any other suggestions. thanks

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No holes and only about 700 ft. I think I will try some other smaller main jet sizes and may pull it out again check the needle position and float. will have to wait for a couple of days when I have more time. Thanks for your help...

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I say, since the snorkle is pulled and it has a UNI filter, go ahead and do the Gordon mod to the exhaust. The "how to" is in a sticky at the top of this forum.

If the bike was originally sold in CA, it most likely has the A16 needle. The 49 state A16A needle has a different taper and is a very popular change to CA bikes.

How long have you had the bike? I'm wondering how old the fuel in the tank is.

Check the spark plug cap to make sure it's firmly attached to the end of the wire.

If you don't do the Gordon exhaust mod, then when you go to experimenting with the main, also try a smaller main, like a 152( 1 size smaller). Gage results between it and a one size bigger than the 155 you had in it to begin with( a 158).

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I had a similar (not the same) issue with mine when I just got it... Mine was sputtering at high RPM and couldn't stay on idle.

The spark plug was loose (I tightened it and that was it)...

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