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Discussion Starter #1
Have read a lot and every seems to extremely helpful, thought I would join so I could join in the discussions. Also to find my new help. Started in quads with old Suzuki 250r's, after about five of these rebuilt I have moved into Honda's 400 ex on my second build and struggling with jetting issues. Glad to be aboard. Thanks to everyone for being so helpful with their post to everyone in need.
 

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Welcome to the forums! What is the jetting problem your having?
 

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Discussion Starter #3
Have an 02 400 ex with a 416 piston 11:1, ported polished head, upgraded valves, stage 2 hot cam, full Curtis spark exhaust, k&n filter with outerwears prefilter, air lid with 6 round filters. Currently have a 42 slow jet and 170 main jet, seems to run lean, crackling top end throttle, and backfire out exhaust on deceleration.
 

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welcome to the forums, slammedranger ^^^, is very good on the sport atvs, your in good hands with him :).
 

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Welcome to the forum, you've come to the right place :)
 

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What is your altitude? And what is your ambient temperature where you live? Sounds almost exactly like my build. You say upgraded valves. Is that +1mm valves? Or just stock size upgraded ones?
 

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Discussion Starter #8
Stock size upgraded valves live in Newark Ohio not sure of altitude, but I do know I'm above ground lol
 

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Wow your not far from the exact same altitude as me. You will want a 45 pilot jet. And most likely a 185-190 main jet. I have +1mm valves and im running a 195. My port job on the head isnt very good though. My engine machinist just touched up some casting and smoothed a few edges

And this is for oem keihin jets. Dont waste your time with anything else. You will also most likely want to drop your needle clip one position.
 
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Yep 1 down from the top which is the fatter side. So 4th slot yes. And no problem always glad to help! Keep us posted how she runs with that jetting. Im betting you will come to the conclusion you have created a monster. LoL
 
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