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Thread: Honda 400ex carb swap

  1. #131

    Default finished my 400ex carb swap!

    OK, so this was the plan...400ex carb (brand new oem Honda part), stock header and muffler pipe (the whole length, right up to where it meets the stock muffler.), Leo Vince GP pro evoII slipon (with the smallest section of its link pipe to mate up to the stock muffler pipe.), (that's from a dual exhaust system from my 2007 Kawasaki z1000. the left can didn't survive the crash so that's how that got donated.), k&n high flow air filter, probably with open air box (ill start with it closed and if it needs to be open, then ill figure out a better mod than just removing the lid. probably do some 1" filter inserts in the intake tube.), also going up to 10" rims for the rear and down to 20x11 holeshots for tires... oh, and i got a 12 tooth front sprocket just for farts and grins.. whats $20 for that kind of wwhheeeee factor.. lol.. but yeah i figure i should be good as is with the carb, but may need to bump up to the 152 or 155 main and/or maybe up to the 42 pilot... oh and i have the cork for the slipon.. that can be in or out... not sure what im thinking there.. have to hear it with it out and if its too loud it will have to go in and ill tune from there, but out would be preferable...
    finished today.. still on stock size wheels and tires all around.. and have not installed the -1 front sprocket yet.. other than that i did all the other mods.. stock jetting, 148 main, 38 pilot, idle screw out 4 turns... cork out, open air box, 1/2 choke, no throttle, 2nd kick sputtered and died, next few kicks the same. turned in the idle screw about 1 & 1/2 turns. didn't really pay attention, but its the idle screw.. easy stuff.. next couple kicks a little better... next kick stays running with some throttle play.. still running, turn choke off, little throttle play for next couple minutes till warm, off throttle and sputtered off... kicked it once, fired up, played with idle screw a little more, went in another 1/2 turn maybe.. started idling nice and after good warm up would rev right up when i stabbed the throttle.... just around my yard and up and down the short little strip of road a few times at my place and it seems super strong, has much better throttle response, and the front seems to come up way easier and smoother.. and very loud, but sounds soooo good.. seems to reach the top of its revs very quickly and stop pulling, but i felt that before the mods too.. i think the gears are just really short.. ill compare to a friends later... someone else mentioned this and went to a 155 main and a 42 pilot, and said it now pulls through the revs better... they also said the pilot jet was out 1 full turn?, but i think they meant the idle screw.. i have almost no seat time on any 350x ever. about an hour last winter and about 2 hours this spring.. neither of which gave any real chance to get to know the machine very well.. so i have no real comparison, but i definitely know that worthy gains have been made.. ill be trying different things with the silencer and air box over the next couple weeks as i have time to go to a friends with more room to move around... then try a couple new plugs to "read" and get a better feel for where its at, but from what i can tell the mods i did are incredible! at some point it will go to a dyno for an a/f ratio, and a horse and torque pull... ill keep you posted...

  2. #132
    Junior Member
    Join Date
    Sep 2013
    Posts
    4

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    The swap is somewhat easy. I had to heat up and reshape some of the plastic for it to fit. But it made a huge difference on my 350

  3. #133
    Junior Member
    Join Date
    Jun 2014
    Posts
    3

    Default

    Hey guys, just finished up my 400ex carb swap! Works awesome really makes a difference. Had a couple little issues with the swap. First was getting the intake boot from the air box to fit over the carb. Had to take a dremel and grind a little out of the inside. Fits perfect now! Wasn't able to get the hard plastic boot from the air box to the frame back on. Due to space issues with the bigger carb. Next was jetting... My motor internals are 100% stock. I have a full chrome dg pipe and a k&n air filter with the air box lid on. I only run super in it. I also live in Maine so I'm at a relatively high altitude. I tried several different jets to get it running perfect. Started with the stock 400ex jets ran like crap. Then went to a 155 main. Ran ok but needed a good warmup before it would run Good. Then went to a 158 main and a 42 pilot with the fuel mixture screw out one full turn. Started up first kick! Runs 100% soooo snappy! Had a issue with the fuel mixture screw apparently u need a special tool to turn it. I ended up using a screw driver at a 45 degree angle to turn it. So if your thinking about doing this you might as well just trough in a 158 Main and a 42 pilot. It's a great starting point and was Super easy to put them in. I got my jets from Rocky Mountain off-road and my carb off ebay.

  4. #134
    Junior Member justoutforarip's Avatar
    Join Date
    Jan 2015
    Location
    Star Lake, NY
    Posts
    13

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    Quote Originally Posted by Eric350x View Post
    So if your thinking about doing this you might as well just trough in a 158 Main and a 42 pilot. It's a great starting point and was Super easy to put them in. I got my jets from Rocky Mountain off-road and my carb off ebay.

    I have the same set up, dg and k&n and a similar altitude so i took your advice and bought 158 main and 42 pilot also from rocky mtn. The jets just arrived, however, the threads on the new jets are smaller and will not fit my stock 400ex keihin carb. The new main jet appears much smaller i'm wondering if they sent me the wrong jet? I did not receive a parts list describing the items in my order... anyone else have good luck with this or some other jet combination?

  5. #135
    Junior Member
    Join Date
    Jan 2019
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    2

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    So many carb ranges in prices on ebay, anyone have a recommendation for a good one to buy?

  6. #136
    Junior Member
    Join Date
    Jan 2019
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    Ok, made a video to help others, with a link to the carb I used in the description, hope this helps someone else!



    https://www.youtube.com/watch?v=6whP0KPUf2A

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