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Thread: 400ex carb on the 350x

  1. #1
    Join Date
    Apr 2014
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    Rhode Island
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    17

    400ex carb on the 350x

    So I've learned how to start my 350x but it still takes a bit of effort to get it to start. I've been watching videos on this carb swap and it seems easy but is it worth it? does it make a difference starting and also what year 400ex should I get? Any info would be great.

    thanks
    Trevor

  2. #2
    JacobMonster's Avatar
    JacobMonster is offline At The Back Of The Pack Arm chair racerFirst time rider
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    May 2015
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    Liberty, Ky
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    226
    Quote Originally Posted by trevorakm View Post
    So I've learned how to start my 350x but it still takes a bit of effort to get it to start. I've been watching videos on this carb swap and it seems easy but is it worth it? does it make a difference starting?

    1. Are there any modifications to the engine, exhaust, or fuel/air system?
    2. When does it give you trouble starting? When it's cold, hot, or both?

    Knowing when you have starting issues will help anyone reading this to help diagnose the issue.

    I dont believe putting the 400EX carb on would make a difference. I'm not familiar with the 350X's but there is plenty of people here who do and will chime in and correct me if I'm wrong.



    Sent from my SM-J337AZ using Tapatalk

  3. #3
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    Apr 2014
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    Motor is stock and runs well. I haven't cleaned the stock carb yet and that may make the difference but keep seeing videos of 350x s starting on first kick without any pumping of the kick start to get it to top dead center.

  4. #4
    JacobMonster's Avatar
    JacobMonster is offline At The Back Of The Pack Arm chair racerFirst time rider
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    Quote Originally Posted by trevorakm View Post
    Motor is stock and runs well. I haven't cleaned the stock carb yet and that may make the difference but keep seeing videos of 350x s starting on first kick without any pumping of the kick start to get it to top dead center.
    Personally, I've never had a cold 4 stroke bike of any kind that started on the first kick. The bikes your seeing could be warmed up or immaculate and fine tuned.

    Does the bike always give you problems starting or just when it's cold? It may need the valves adjusted.

    Sent from my SM-J337AZ using Tapatalk

  5. #5
    Join Date
    Jan 2017
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    Shawnigan Lake, BC
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    I'm sure one of the guys running a 400ex carb will chime in, but I think the advantage to that carb swap is an accelerator pump built in, which helps with throttle response without sacrificing idle settings.

    As far as starting, when I first got my 350x, it took forever to start. When hot and trying to restart it, 10-15 minutes,lol. Total dead leg.

    Then I learned how to start it, and it worked, but was still a PITA.

    I don't know what changed other than seat time, but I can start it 2-3 kicks, cold/hot/whatever. If a buddy hops on it, even if I tell them how to do it, they struggle. Mine likes WOT as you kick down, but released right as it fires.

    If the decompression cable and valves are set right, you just gotta ride it.


    Sent from my SM-T560NU using Tapatalk

  6. #6
    Join Date
    Apr 2014
    Location
    Rhode Island
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    It's not that bad but used to more immediate starting, technology has advanced since 85'. Can't wait to get her out but want to go through it first. All part of the learning curve for anything. I can tell it needs new axle bearings and while doing will replace the sprockets and chain, after that I can slow on the refurb and enjoy it, after that its forks.

    Thanks

    Trevor

  7. #7
    Join Date
    Jun 2009
    Location
    Leander TX
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    2,181
    I bumped the pilot jet in my stock 85 up a size or 2. I can't remember the numbers anymore (it's either a 40 or 42 in there now). That seemed to help starts. These are jetted lean from Honda.

  8. #8
    Join Date
    Apr 2014
    Location
    Rhode Island
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    17
    Yeah took me a few starts to figure out how easily these flood. I have been putting choke half way on and can get it to start and then other times I then have to take the choke off and then it starts. Always with the motor being pumped with the kick starter till it gets to TDC. Once warm it's a toss up if she wants choke on or not, mostly not. The machine came from AZ at a higher altitude so being close to sea level now the carb may need cleaning to more fuel flowing wioth out the choke on. anyway thanks for the responses and keep them coming, all good.

    Trevor

  9. #9
    Join Date
    Apr 2012
    Location
    MI, USA
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    3,091
    Mine just has a DG exhaust (prefer stock though), and mine's on stock jetting so leaner than I should have it. Cold starts takes 2-3 kicks on full choke. Hot starts are 1 kick. I don't touch the throttle normally, maybe just a tiny bit like a high idle set (1/8 throttle). The choke on the 350x seems to flood easy if you give it any gas. This is with fresh gas, and I run the carb out of gas when I put the machine away. My decompression cable works super good, I can just get on it and kick, no looking for top dead center etc and the kick feels the same as if you pulled the spark plug out.

    My other 350x starts about the exact same way, but the lever that goes into the head is messed up and doesn't open the exhaust valve at all. On that engine I have to find compression stroke, push it just past top dead center, then kick it. It has so much compression, I can nearly stand on the kick starter on compression stroke. Pretty sure it's all stock engine and has OEM exhaust.

    I don't think the 400ex carb would help with cold starts, it does have the accelerator pump though so you get a much faster response since it squirts a little gas when you floor it to offset the vacuum drop. My machines seem to respond fine in stock form, but I could see them lacking if the engine was built up more or if the machine is actually used for racing you'd want every little bit of performance possible.

    I've heard from several sources these machines were jetted lean. My 85's have 138 main jets, I've read 86's came with 142 main jet. Not sure about the pilot, probably the same story though.


    There's a bit of an art behind tuning a carb, learning how to do it, or use an exhaust gas analyzer to tell you what to do will get the best performance out of your engine and likely the easiest starting assuming the choke works good.


    I read similar issues with Dolmar and Mikita chain saws, but they have a bit of a science to them, choke, 3 pulls, take choke off (high idle is set automatically), pull 1-2 times and it will fire up. If not the carb needs tuned, or you ran it out of gas the last time it ran etc. Hot start is just pull it, if it doesn't start, set high idle (choke and unchoke it) and pull again.


    Oh yea, FYI, the choke on the 350x pops off sometimes on it's own, at least on my machine it does. I think normally it's worst with half choke.

  10. #10
    Join Date
    Apr 2014
    Location
    Rhode Island
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    17
    thanks for the responses. Anyone have a good source for the 142 main jet? I'll skip the carb change out. Once running she just idles nice and I won't muck with it until I get to cleaning the carb.

    Trevor

  11. #11
    Join Date
    Apr 2012
    Location
    MI, USA
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    3,091
    I've had good experience with https://www.jetsrus.com/a_jet_kit_at...50_ATC350X.htm

    Be sure to buy the Genuine jets, not the "OEM Equivalent". The non-Genuine ones likely are not using the same sizing system (super stupid I know), so either stick with OEM, or buy a bunch of aftermarket sizes to run through the sizes to see what number in their system you need.

    Wouldn't hurt to buy both the pilot jet and main jet. The service manual says stock sizes are 138 main, and 45 pilot.

    Don't toss your old jets, since you never know if you'll need a jet super badly and can't wait for shipping to get the machine going. Generally they just get dirty and go leaner than normal. Over time they erode and get larger, or corrode with the ethanol in the gas (run ethanol free if possible, it's way better on your carb). If you stick with the typical pump gas (E10 effectively), every time you stop riding your machine for the day, turn the gas tank valve off and run the carb out of gas.

  12. #12
    Join Date
    Apr 2014
    Location
    Rhode Island
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    17
    good to know about the fuel shutoff. and thanks for the site for the jets. As far as the ethanol it just sucks. I been avoiding it for years till the last closest place stopped carrying ethanol free fuel. It was the worst for the argo with stock briggs and stratton motors. B&S have their own fuel additive and I have been adding that to the gas and no issues anymore. I tried all the others sea foam.......etc but none work as well as the B&S additive.

    Trevor

  13. #13
    Join Date
    Apr 2012
    Location
    MI, USA
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    3,091
    I never tried it or got the MSDS for the pump gas, but it's possible to add a little bit of water and it will make the ethanol separate out. The bad part is, any additives that are water soluble would be removed as well, and 87 octane fuel would drop down a bit like 85-86 so you'd need probably mid grade to start with.

    Any idea what's in the B&S additive? I'm not much of a Brigs fan, but maybe they figured something out.I know HEET and such is pretty pointless since you're basically just adding more ethanol in.

    I must be lucky with my location, there's at least two gas stations near me that has ethanol free fuel, runs about $1 more and is 90 octane. Stuff works great in chain saws, mowers, and atvs. I'm tempted to try it in my 1990 Lexus LS400 to see what the MPG difference is, but I highly doubt it can give me enough MPG boost to offset the higher costs. Not sure the the car was designed for E10 fuel or not, guessing not since it has a steel fuel tank.

    I don't think sea foam has anything in it to treat E10 fuel for non-E10 machines, pretty sure it's more like an injector cleaner and engine cleaner type of formula.

  14. #14
    Join Date
    Apr 2014
    Location
    Rhode Island
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    17
    No idea what's in it was just relieved to not deal with the ethanol gumming up the carb anymore. I have had the same gas in my argo with this additive in it for about a year and a half and she will start up and run fine. I'm sold on the B&S additive.

  15. #15
    Join Date
    Apr 2012
    Location
    MI, USA
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    3,091
    FYI, E free gas is the type that gums up, turns kind of a brownish color and smells like turpentine, but it normally takes multi years for it to get to that kind of state. It's almost like a jelly in the carb and super easy to clean.

    Ethanol is very corrosive and draws in moisture from the air and seperates in the bottom of the float bowl. It causes the white powder (aluminum oxidizing) and can wick up jets and plug them with the oxidizing dust when you go to start the machine. Royal pain to clean these carbs, basically every passage, jet etc has to be taken out and cleaned. I miss the days of just taking a carb float bowl off, spray it down with carb clean and re assemble and 90% of the time it's good to go.

    Anyway if the additive is helping that's a great thing. I'd assume it's some sort of anti corrosive or something to stop the ethanol from separating out with the air moisture so it's effects are reduced a lot.

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