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2-to-1 carb

Discussion in 'The Garage' started by skillzman1, Jan 8, 2011.

  1. isigt

    isigt XS400 Addict

    I also rode mx for many years. only time the throttle got stuck for me was after a heavy crash. But that was because the throttle grip was smashed to pieces and wouldn't move. :)
    so +1 here as well.
  2. while we are discussing carbs...I pulled mine apart to clean them...I had 135 mains in both carbs...and the pilots I couldn't tell ...what are the jets in the air inlet near the filter flange for..they were marked 155?
    I'm going with pods and hopefully a 2-1 exhaust....at 300 feet above sea level I'm seeing alot of varying opinions on jetting.
    So...the million dollar question is ...whats a baseline setting for the rebuild.
    main jet size?
    air jet?
    how many turns on the screws?
    I know its been asked before...but humor me if you would...I'd like to get the necessary stuff when I buy the rebuild gaskets etc,..and not get hung up by waiting for little tiny things that will hold the build up longer...time is a hot commodity nowadays.
    I have a buddy thats good with tumning..but I need to get it in the right ballpark so we're not wasting time.
  3. unkempt

    unkempt XS400 New Member

    I started building a single carb intake for my xs400 g then abandoned the project after reading a post about it working for a 180 degree crank (xs650) and not a 360 degree crank (xs400) because the intakes are partially open at the same time. Has anyone successfully ran a single carb on an xs400?
  4. FlyingAnvil

    FlyingAnvil XS400 Addict

  5. eric123

    eric123 XS400 Addict

    The xs650 is a 360 degree crank and the xs400 is a 180 degree crank...
  6. drewpy

    drewpy Excess twin Top Contributor

  7. FlyingAnvil

    FlyingAnvil XS400 Addict

    You mean every other stroke is taking in fuel as opposed to only 1 out of 4 strokes, I mean that kind of makes sense. Would the CFM formula be different for a two stroke? I am only familiar with the 4 stroke formula. Thank you for explaining some of this. I find it very interesting.
  8. bcware

    bcware Well-read Top Contributor

    Two-stroke engines fire once every revolution (four-stroke engines fire once every other revolution). This gives two-stroke engines a significant power boost. Two-stroke engines have the potential for about twice the power in the same size because there are twice as many power strokes per revolution.

    Here is a simple, to-the-point, comparison between 2 and 4 stroke engines: http://www.deepscience.com/articles/engines.html

    Formulas: http://www.nightrider.com/biketech/calc_formulas_page.htm

    I think the CFM formula might be doubled. It is hard to search for in google because of the terms being used.
  9. FlyingAnvil

    FlyingAnvil XS400 Addict

    OK I am starting to understand this a little better thank you. Never really messed with the 2 strokes except for chain saws and never hot rodded one out.
  10. drewpy

    drewpy Excess twin Top Contributor

    ..and that's with getting into tuned exhaust pipes (expansion pipes) for the 2 strokes!
  11. unkempt

    unkempt XS400 New Member

    Right right, i had it backwards. So you can put a single carb intake on a 180 degree crank. Im going to try to finish it and give it a try with a vm34.:thumbsup:
  12. eric123

    eric123 XS400 Addict

    A single carb will work on both...With the 180 degree crank, I suppose theoretically the second cylinder to fire, could be leaner than the first cylinder...
    Last edited: Nov 15, 2011
  13. tgp---

    tgp--- XS400 Member

    Interesting Thread

    DCopp, I would like to see a little more info on what you did on your 2to1 manifold. Looks like you made it out of aluminum. Were those pre-made flanges you used? and what diameter is that??

    Anyone else have any success? maybe w/stock carb?
  14. D-Train

    D-Train D-Train

    rad hose isn't rated for gas use it will break down. i used a snowmobile carb flange on mine and it works great
  15. What did you end up running for your main jet size on this single carb setup with the stock carb?
  16. D-Train

    D-Train D-Train

    I just road tested my 81 xs400 with a single carb and to my disappointment it runs way to lean on the left side and to rich on the right, since there's only one mixture screw i don't know how I'm suppost to fix this. Anybody have any ideas. Also like someone else may of asked already has anyone actually successufully done a single carb on a xs400?
  17. 01ps

    01ps XS400 Addict

    What does your intake look like?
  18. gentlemanjim

    gentlemanjim More Wrenchin than Ridin

    Sounds like you have an air/vacuum leak on the the lean cylinder side. One carb will provide an equal fuel mixture to both cylinders. Check for the leak by spraying carb cleaner, WS40 around that side of the intake.
  19. D-Train

    D-Train D-Train

    hey 01ps my intake looks like a "Y". Thanks gentlemanjim I never thought of checking that.

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