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cv-vm pcv nono fuel line no gogo

Discussion in 'The Garage' started by Noidea, Sep 9, 2019.

  1. Noidea

    Noidea XS650 Addict

    Hello all, hope everyones alright. I been on hiatus because my job during summer i cant really do anything working up to 16 hours a day. But im back at it i bit the bullet and purchased vm34s . Not bad easy to put them on and take off and look good. I still have an issue with a sucking noise on my right side it sound as though it comes from the air filter. I got to thinking that it was my engine breather cause i have a hose coming out the right side and the left side is plugged . Ive read all about people using one way valves and plugging one side or completely swapping those breather tubes out for later models because of issues with oil leaks while riding. But has anyone ever experinced that sucking noise due to the pcv valves? considering the carbs are brand new as well as the manifolds I figured it ok to eliminate that thought of leaks from my mind. i tried to just remove the plug and the hose see if that noise is there and it was .Not sure what it would be.

    Alsoo silly/stupid question. when connecting fuel line from the vm carbs to the petcock is there some kind of theory with uneven pressure i should be aware of? I have it running from each petcock separately with a fuel filter and clear fuel line just a right angle and when i turn the switch to on I get no gas if I unplug the line it comes flowing out as it should. I have gravity petcocks. When I tested the bike with new carbs it had a slight leak at the lines cause the hose was to big which is the only reason i feel it was flowing but with a tight fitting line it seems like theres some suction issue or soemthing preventing fuel flow.
     
  2. azman857

    azman857 '80 XS 650SG Rider Top Contributor

    Venting OK at the tank cap?
     
    lakeview and grizld1 like this.
  3. Noidea

    Noidea XS650 Addict

    Yea open the gas cap wide open and no dice
     
  4. grizld1

    grizld1 Grumpy old man Top Contributor

    Have you leveled the bike and checked fuel level in the float bowls with a sight tube (should be no higher than the bottom of the carb body flange, no lower than 2 mm.below that line)? If fuel level checks out, fuel flow probably isn't the problem. Make sure vent lines on the VMs are unobstructed.
     
  5. Noidea

    Noidea XS650 Addict

    I honestly have not considering they're brand new carbs. It said tuned for xs650 I understand they're not gonna be tuned exatcly to my bike but didn't think the floats would be that off. I can check when I get a Chance seems reasonable I'll just set att the settings to stock using that mikuni tune book I read a tad on. Will also check vent lines. If it works or doesn't I'll let you know thanks :)
     
  6. grizld1

    grizld1 Grumpy old man Top Contributor

    One more time: The first thing to do with any new aftermarket carburetor is to strip it, clean it (yes, even new Mikuni and Keihin carbs can have manufacturing debris left in them), and inspect fuel level. The floats have been bouncing around in shipping with no liquid to buffer their movement and it's common to find fuel level well out of range. To set float level in your VM34s, move the arms of the actuator and leave the tang strictly alone.

    Edit: If you use float level measurement instead of a sight tube, be sure to take measurements at the points on the actuator arms where they contact the horizontal pins on the floats.
     
    gggGary likes this.
  7. Noidea

    Noidea XS650 Addict

    Damn thank a lot I'll defiantly do that probably tomdo! Do you so happen to have any references for newbies to vm carbs or a thread to follow I understand the bs38s pretty well never dealt with these bad boys I'm very new to them.
     
  8. grizld1

    grizld1 Grumpy old man Top Contributor

    Be careful of those jet lists! There's a lot that isn't said: performance mods (cam, displacement, intake, exhaust, compression), fuel, elevation, and intended use. You can fish for recipes, but IMO you're better off working the steps. Use the Tech button and the search function, it works really well on this site.
     
    gggGary likes this.
  9. Noidea

    Noidea XS650 Addict

    Yea i understand. thanks for the thread too. @grizld1 you were correct about the float height being off it defiantly influence the fuel coming out properly. i set them to 22mm for now the left one flows freely but the right still gets caught even when the bike is level gonna try to just raise it a hair tommorow see if that does anything. Theres still that strange sucking noise that i just cant shake gotta figure out the baseline settings on these carbs for my bike first than ill go deeper into that. When you said you be sure to take my measurement where they contact the horizontal pins on the float im not sure what you meant exactly.I just used the tang just like in the bs38s than measured the ends of the arms as used that as my measurement. gonna do bunch of reading/ research tonight will also go through that thread. See what i can find and put it into use for tommorow.
     
  10. grizld1

    grizld1 Grumpy old man Top Contributor

    Each float has a pin on its side. When the float rises, the pin contacts the actuator arm. The point of contact is where float height is measured.
     
    Noidea likes this.

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