Carby New fuel valve - engine now runs rich!

Discussion in '2-Stroke Engines' started by Pablo, Jul 1, 2008.

  1. Pablo

    Pablo Motored Bikes Sponsor

    New fuel valve - engine now runs rich!

    Is this even plausible? Plug now looks rich, engine sounds and runs rich.... At mid and fuel throttle. I had the thing running nearly PERFECT before.

    My fuel petcock snapped off last Friday. It was the usual piece of junk cast pot metal HT valve. So I did a little research and got a nice solid brass ball valve. Installed like a champ. The fuel flow through this thing like a fire hose! I guess I never thought much about how bad the old valve was (until it snapped) - BTW I never used the POS intank screen and my plastic "VW" clear fuel filter has caught a good amount of crud. Now here's the weird part, the filter would only be 1/2 full of fuel at best when the bike was new and got worse with time. Recently the filter just would have just a tiny amount of fuel in it - enough to run really great with zero problems. Change the valve and it runs rich.

    I don't understand why. Maybe the fuel flow was metered by the valve not the carb :p that just sounds whacked.....

    Anyways - I will move the e-clip up one notch and see what gives!

    Lemme know your thoughts.
    Last edited by a moderator: Dec 15, 2015

  2. I took the screen off mine also. The fuel just trickles out of it, and the filter would only fill up half way. I just installed a 18mm mikuni carb and am in the process of jetting, but I noticed it fills up the filter, hmmmmmmm. Maybe the vent in the mikuni? I have a hole drilled in gas cap, but it didnt seem to increase flow with stock carby, so I dont know if that would matter....
  3. Pablo

    Pablo Motored Bikes Sponsor

    Interesting - I went for a ride. Seems just a little gas fat.....too tired to mess with the carb right now.
  4. Pablo

    Pablo Motored Bikes Sponsor

    So I went up to top notch, sure as anything it runs better than ever!! Sweet. Problem!
  5. eljefino

    eljefino Member

    I'm working on a theory about surface tension, tiny bubbles, gas flowing or not flowing, and that valve.

    It is still nascent.
  6. Boomer

    Boomer New Member

    Where did you get your new valve?
    I replaced mine with Dax's upgraded petcock and still can't decent fuel flow. I have to pump air into the tank and that gets the line half full and it will either stay at that level or drop all the way to the carb. I've had this carb apart a few times now to see if there was any dirt in the float chamber intake valve and it's always been clean. I was wondering if I could drill out that intake valve a bit to alleviate and surface tension the fuel might have. Just can't get good fuel flow. I'm also wondering how much the screen filter in the tank restricts flow, tried using an inline filter, that would only fill up halfway and for some reason one side of the screen collapsed.
    Last edited: Aug 7, 2008
  7. Pablo

    Pablo Motored Bikes Sponsor