XR400 pilot and airscrew

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#1
I bought my bike almost 2 months ago. The mods are WB 416 kit, K&N, snorkel out, and FMF exhaust. The bike was jetted with a 65 pilot, and 165 main. The bike felt too rich off the bottom, so I ordered a new pilot, and a new needle (A16A) because I bent the old one. When I put the new needle and pilot (62) in the bike, it felt MUCH better. It's now very easy to loft the front wheel over logs. My problem is, when trying to set the airscrew by turning it to get the highest RPM's, i end up closing the airscrew. So do I need to go back to the 65 pilot? I'm also having a hard time getting the bike to idle at a consistent speed. It wants to idle high, but then if I just blip the throttle, the idle drops down. Could that be because it's too lean? The plug at last check looked much better than it used to . The tip is I guess you could say kinda gray/brown? Before the jetting change, it was totally black. Oh, I ride usually close to sea level to 1000 feet.

Jeremy
 
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#2
Jeremy,

Sounds similar to what I've got going on with my KLX. How far out is your pilot fuel screw? If the air screw is all the way in, you are running lean, but perhaps the pilot fuel screw can bring it back with spec. If not, I'd try the 65 pilot again with the new needle.

As for the idle, I've got the exact same problem (see my thumper pumper post). If you figure it out, please let me know.

Mark
 
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#3
xr400

:) You need to check out the power flow intake system by Ron Mc Cord of Billings MT his ad is in the back of dirt bike mag. My xr400r runs better than a 440 kit with pumper carb for@ $250.00
 

fremontguy

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#4
Seems to me if you have to turn the fuel screw in all the way for good idle, you would need to go leaner on pilot jet. I have similar mods on xr4 and run 58p, 158m, and a16 #2 for all altitudes.
 
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#5
What Freemont guy said. And you have to remember you have a "fuel" screw, not an air screw so you have to get your thinking straight. When you close that screw it's less fuel, not less air.
 

mtngoat

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#6
Try turning your idle knob down to a low idle and then adjust your pilot screw per the manual. Start around 1.5 turns from closed. You should not have to return to the larger pilot jet.
 

TexKDX

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#7
Originally posted by Hondaxrguy
I'm also having a hard time getting the bike to idle at a consistent speed. It wants to idle high, but then if I just blip the throttle, the idle drops down. Could that be because it's too lean? Jeremy
This generally means lean right off the bottom, Jer. First try lowering the idle just a bit, then give it 1/2 turn OUT on the FUEL screw. Before attempting this, make sure the bike is fully warmed up, say after 15 minutes of regular riding.

My 250 idle is a bit irregular until it is totally warmed up. I also seem to play alot with the idle screw between starting it and riding fully warm. Guess that is why they put that big black knob on it ;) . My idle is most variable when it is turned up just a little too much. I like to let mine warm up at a fast idle until the oil lines are hot ot the touch. I'll idle it back down, but the motor is not fully hot yet so I end up messing with the idle one more time.

Another sign of lean off the bottom (pilot) is closed throttle backfiring upon deceleration. Do you have any of this? Sometimes raising the idle a tad will make this go away. If not, again a little further out on the fuel screw may.

If these steps don't fix it, then go up a half size on the pilot, set your fuel screw at 2 turns out, and start over.

Hope this helps,
 
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#8
Thanks for the replies!

Ok, I just went out to mess with the fuel screw again. Before I started the bike, I turned the screw out 1.5 turns. It was closed. I started the bike, and let it warm up fully, then rode it around the yard for a few minutes. I then started moving the screw out, and didn't really see any effect in idle, so I started turning back in ( I was going in half turn increments). I didn't notice any idle change until I was about 1 turn out. Then the idle really started to climb and continued climbing as I went in until it was completely closed again. I probably gained about 500-1,000 RPM's before it closed. So, I need to get a leaner pilot still? Should 60 be good? Or should I go straight to 58? That seems like it would be a pretty big jump to a 58. I'd rather be on the rich side than the lean side, as I do occasionally go higher in altitude. Thanks a lot guys for the help. BTW, my bike is a 98. Forgot to mention that before.

Jeremy
 

TexKDX

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#9
Re: Thanks for the replies!

Originally posted by Hondaxrguy
I'd rather be on the rich side than the lean side, as I do occasionally go higher in altitude.
Jeremy
If you go to higher altitude then you'd be better off on the lean side than rich, if you deviate from ideal for your current elevation. Higher elevation = leaner jetting requirements.

This is still not enough info to tell us if the bike is jetted correctly, Jer. Ride it for real at 1.5 turns out and go from there. A totally closed fuel screw is gonna give you problems any way you cut it.
 
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#10
stupid mistake

I don't know why I said richer for elevation. I know you need to jet leaner. Just cut that out. :cool:

Well, I may be able to ride tomorrow night. I'll see.

Jeremy