simple 400SX mods?

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Nov 20, 2000
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#1
I have a still new-to-me '01 400 sx and I recall there were some simple mods like plugging some tube on the carb and rerouting another (vent?) to the airbox. I have an after market filter and a FMF Powercore IV, changed the gearing to 13/54 on the bike and otherwise it's stock. Any detailed directions would be appreciated. I'm just in luv with this bike btw...
 
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Mar 19, 2001
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#2
Here's what I did on my new 400SX.

14-54 gearing for motocross
13-52 gearing for off-road

Pro Circuit T4 Exhaust

Jetting Specs
OCEMN needle, 3rd clip
168 main
fuel screw 1 turn out

I installed an Emgo filter on the crankcase breather hose and placed it under the fuel tank. My dealer had a plug that fits right on the spigot on the card that the crankcase breather hose fit on. Putting it under the fuel tank would be a better idea but would require a longer hose to reach back that far.
 
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#3
I installed the Pro Circuit T4 silencer and changed the jetting to an EMN needle-#4, and a 168 main. I also dropped the gearing to a 13/50 combination, mostly to make it easier to ride in tight off road stuff. I may cosider adding a few teeth on the rear sprocket for laughs. As it sits right now, I can out run an '01 CR250 in 5th gear....and I still have 6th to go :cool: !

Coach,
what altitude are you at and have you fiddled with the jetting much, or did you just install it and go? (I installed my jetting as per recommendations and it ran great , so I haven't messed with it yet.) Also, I'm a little confused on the crank breather thing; you plugged the spigot on the carb and placed a filter on the breather hose which you place under the gas tank, correct?
 
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#4
Thanks for both of your informative posts -- I'll talk to the dealer on the carb parts and see if they have the breather/plug too. The gearing I'm happy with (tho I'd luv a stump puller 1st, if I had just one wish). I'll let you know how the results turn out!
 
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#5
Bud-man,

I'm at about 900' above sea level. I have tested alot of different jetting specs. I messed around alot with needle position and main jets. You can go all the way down to a 162 on the main. It will really help the overrev but take away from the grunt on the bottom. Great for faster, loamy motocross tracks. The richer the main, the better the bottom end grunt, but at the cost of the overrev on the top. I run a 168 for off-road type events and a 165 or 162 for motocross.

You are correct. I placed it under the tank but placing it in the airbox would be a better idea. I must have had alot on my mind when I typed that post!!!:confused:
 
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#6
Thanks Coach! I haven't experimented much with the jetting as I haven't had much time. I ride at similar altitudes (~1000ft) and have the same exhaust (T4 w/2" tip) so this info helps. You mentioned that you had better top end with smaller main jets, but the bottom suffered. Did you try a larger pilot jet to see if it helped to compensate? I tried moving my needle clip from the 4th to the 3rd position but feel that it suffered in performance. Not a lot, but now the bike had a "bog" when I grabed a lot of throttle when the rpms were very low. I don't remember this happening before.
 
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#7
I haven't changed out any pilot jets. The bike works so great that I have to force myself to sit in the garage to work on it at all....all I wanna do is ride it!!!:p