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XR400R Carb Jetting - HELP!!

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Posted by: JJAMES1962---------------------

I currently have a 2002 XR400R and have placed a Supertrap race series exhaust on it. I am also placing a K&N airfilter on the intake side so my breathing should improve dramatically. I think I understand that the stock main jet is a #165. I have purchased a #175, #178, #180, #182, #185 to "TUNE" the system. Does anyone have any comments/help with me trying to get this beast set-up? I have 8 - 14 rings to work with on the exhaust and would like to have a little xr400 experience chime in on the base set-up. Am I wrong on the jetting sizes for "Tinkering"?? Should I try any smaller jet sizes?? Anyone with Supertrapp experience on this bike??

Just asking for some guidence and help

Thanks,

Jeff


Posted by: JJAMES1962---------------------

Quote:
Originally Posted by JJAMES1962
I currently have a 2002 XR400R I think I understand that the stock main jet is a #165. I have purchased a #175, #178, #180, #182, #185 to "TUNE" the system.


OK, I went out for a ride and went to install the new jets after I replaced the air cleaner and opened up the exhaust a little more with a total of 12 rings on the Supertrap exhaust. The stock jet that came out was a "142" not a 165, making the extra jets I got much too big. Uggghhhh!!!! Took me about an hour of looking in Mena, AR. (population next to zero) and I found a 158 & 160. Got them Both. I installed the 158 first. Ran much better but still a low end hesitation on initial throttle. The weather was cold (30 deg), wet and rainy so our riding was limited due to conditions. My XR400R definitely WOKE-UP but not entirely. Any suggestion for more improvements without going to a 440 kit from thumper for $750.00 plus?

Any responses would be greatly appreciated


Posted by: Patman---------------------

I might be selling a Mikuni TM33 pumper carb setup with cables, air boot, and boot adapter depending if I can get it sorted out on my 284 or not. Right now I've lost a lot of the bottom end snap that I really like with switching to the 33 on this bike. It might be just what you want for a 400, it will for sure take care of the low end hesitation the 400's seem to have. I'll know in a week or so.


Posted by: adam46---------------------

make sure the air snorket is out-i took a saw-zall to mine afterwards and cut the whole box open-way more air!yes, the mikuni pumper carb will also take care of any jetting problems(one of the best upgrades you can do for the xr400


Posted by: Trailryder42---------------------

Also, swaping the main jet isn't going to fix the off-idle hesitation. You need to play with the pilot jet and fuel screw for that.

ALWAYS give your elevation when asking jetting questions.

As suggested, if not already done, remove the snorkle under the seat.

I've never known an XR400 that needed richer than 165/65 jetting at sea level, no matter how it was setup. If you're above sea level, you'll be leaner than that.

My intake and exhaust modded XR4 ran primo at 3600' with 155/55 jetting, so go from there to help in determining yours.


Posted by: JJAMES1962---------------------

My snorkel has been gone since day one. Upon more in-depth reading. It has been said that the 160 size jet on the carb it optimum. I generally ride in the Dallas Area but sometime get over to the Quachita Mountain (low range) in Mena Arkansas. Much fun unless you run out of fuel. I would definitely be interested in that Mikuni Carb if the price is right. Where are you located Just dropped way too much on my street bike as well as the wife keeps taking my money to feed those kids. Something about they have to eat more than once a week????? Oh Well......... How/What do I need to get at that smaller jet. Should I just pull the carb or can I get at it by pulling float bowl? I did install a K&N air filter and was thinking about a sprocket/chain upgrade. - ANY thoughts??

Any thoughts on that Supertrapp exhaust. Good?? So-So?? Garbage??

Thanks for all the responses as it has been a while since I have tore into bike Carbs!!

Thanks,

Jeff


Posted by: Patman---------------------

JJames, shoot me an email at pat ("at") pitvipermx.com and we'll hook up on the carb setup, it's just too much carb on the bottom but the upper end is improved.


Posted by: JJAMES1962---------------------

Thanks Pat,

I sent you an E-mail

Jeff



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