Intake air leak - carburetor - intake - pics

Discussion in '2-Stroke Engines' started by tirebiter, Dec 15, 2006.

  1. tirebiter

    tirebiter Guest

    When I read Blompod's "Not Idling?" thread it reminded me about something I found when I checked the intake to carb fit my bikes. That might not be his problem tho.

    Here's something I found on all my kits. If you assemble the intake and the carb just the way they come, the carb can't fit all of the way onto the intake tube. There's a pretty good sized leak at the bottoms of the grooves in the carb flange. Each kit's a little different but on the one in the pics the tube can only go into the carb .420" before it hits the weld on the tube. The grooves are .500" long which leaves .080" of the groove uncovered. The clamp on the outside doesn't cover the grooves either but that doesn't really matter because air will leak down the grooves anyway if the carb doesn't slip on at least past the ends of the grooves. Air leaks on the intake are not good. :evil:

    On the bike I ride I smoothed the weld all the way to the bend and also ground a little off the end of the carb flange. That way I could slip the tube in until it bottomed out. Maybe I'm a little fussy but I thought I'd bring it up in case someone else is fussy too. :wink:

    Here's some pics of the measurements I just took off a fresh kit.



  2. jonylevers

    jonylevers New Member

    spot on tirebiter !! have done the same on my engine though i still have issues with flooding at present-may have to equip motor with 70cc sports carb though at 110mm it may be awkward to fit.
  3. Bronzebird

    Bronzebird Member

    Have you checked out the float valve or float level?

    I have found a small pieces of debris on the valve seat or on the float valve. Or any bind in smooth operation. Float level is checked next.
  4. Bronzebird

    Bronzebird Member

    I have an o-ring at base for snug seal.

    Great idea to clean parts and check fit.
  5. jonylevers

    jonylevers New Member

    g'day bronzebird - i must have striped the carb down 5 times now believing the same ,have set float 2mm above jet, i even made up a gasket for the fuel primer base ! its annoying as motor has just been run in,have ordered another carbi from Zbox after reading a few posts.
    have moved E clip on needle 1 down and 1 up from factory settings though to no avail it seems no matter what i do the results are the same-bike starts-runs ok 4 a bit then power starts to die with throttle open fully !! fuel can be seen on chain guard,now using NGK B6HS plug problem is still the same !

  6. I would suggest a good inline fuel filter if you dont have one already. And the other is the oring seal. I even use that on the Mikuni carb I installed, that way you really dont have to mess with RTV as the end of the manifold seats against the oring for the seal....
    Last edited: Aug 18, 2008
  7. Bronzebird

    Bronzebird Member

    Inline fuel filter, rinsed fuel tank, debris must have fallen into carb tube during shipping or installation. Thats when I noticed the poor seal at clamp to intake manifold. 9/16th O-ring fitted nicely onto carb with a touch of high temp "ultra black" RTV. Also used RTV on exhaust gasket as it leaked on next ride which is number seven under my belt. Head gasket is starting to seat very nicely and minimum retourq finally.
  8. jonylevers

    jonylevers New Member

    got it !! have also sealed where the cable enters carbi as another potential air leak won't know till tomorrow if its a winner!!
  9. ra42mario

    ra42mario New Member

    So has ANYBODY found at where to seal all these air leaks on this carb? I've had my bike for three weeks and will still not idle. I can put the clutch in and rev the bike to keep it running and spray starting fluid on the carb and it chokes it out, so its sucking it in. So far I've choked it by spraying on the carb intake tube and the throttle cable hole.

    I put two oil drain plug gaskets RTV'd together in the intake tube to seal up the carb, it has helped and when I spray the starter fluid there it doesn't choke up, but it still won't idle. There are more air leaks somewhere.

    Who sells the best carb? I'm just about sick of this one I got on here. The bike is losing power and the no idle is annoying. Next carb I get I"m just going to JB Weld the intake tube to the carb so it never leaks.
  10. Hawaii_Ed

    Hawaii_Ed Member

    JB weld will work :) How old is your engine? Could also by a base gasket leak. Throttle cable should not be much of an issue. Does adjusting your idle screw change idle at all? Can also tighten up the throttle cable to hold it open more, but that is not ideal. Also check your fuel flow, I have had two with petcock problems. Take the intank filter out and see if it helps.
  11. ra42mario

    ra42mario New Member

    my idle screw does not do anything when i adjust it out or move it in.

    My in take filter is out and actually when i close my petcock the fuel still dribbles out at a pretty good rate so i think its not functioning properly.

    As i said earlier too, i readjust my float so it doesn't leak all out, and its fine for a while. I then ride the bike and park it and the gas just spills out of the air filter. I'm confused and frustrated with this carb.
  12. Hawaii_Ed

    Hawaii_Ed Member

    Sounds like a def problem with the float/needle valve. Not sure what is messed up on it, but something is making it stick open. Ever find fuel in the float like a leak? Carbs are pretty cheap, I have a spare I know works fine if it helps, or get a new one :)
  13. ra42mario

    ra42mario New Member

    I think so too Ed. Because the bike ran STRONG a few day ago, and is gutless now. I think my little brother may of tipped the bike over (I built it for him) and isn't saying anything. I only suspect that because of a scratch on the tank.
  14. biken stins

    biken stins Member

    did you check the float to see nothing had filled it ?
    Dirt holding primer button open ?
    Good luck
  15. Just_Gasit

    Just_Gasit Member

    A fix for the original post it to add an o-ring down the hole with the clamp. As you tighten the clamp, push the carb toward the cylinder and it will seal all those groves. The o-ring must of course fit correctly into the end of the carb, not too small or too large. In the original post picture of the carb, the o-ring should sit on that ledge below the groves.
  16. danhill

    danhill New Member

    I have a sinking suspicious that air leaks may be responsable for my somewhat low power output.

    Anyone have a good method for finding out where leaks are? I would stick my ear down by it and listen for vaccum but somehow I don't think that will do it haha.

    I am just now starting to run my engine a bit further than around the block. After about 3/4 of a mile I am getting severe power loss. I am not sure if this could be air problems but just looking at the little carb makes me think it has to be guilty in some way for all my lifes problems.
  17. EnFlaMEd

    EnFlaMEd Member

    Use an engine starting fluid such as aerostart or "start ya *******" preferably with the little hose so you can direct it around any suspicious areas. If RPM changes when sprayed on a certain area then there is a leak there.

    I had a lot of air leaks on my bike. Now I have used copper gasket sealent at the manifold to jug flange and the manifold to carbi flange. I have also put an O-ring in the carbi flange and found that the same size can be used for the cap that screws down ontop of the carb where the throttle cable comes in. I actually had a big leak there but now with the cap screwed down tight and the o-ring in there its all good.

  18. danhill

    danhill New Member

    Sounds easy enough to track them down that way.

    O-ring and copper gasket gunk sounds like a good idea. I was kinda wondering about the lack of gaskets on the carb.

    I can rebuild a chevy carb but this **** thing with its dozen parts is more frustrating than the auto ones have ever been ha.
  19. goodtime65

    goodtime65 Member

    carb flooding

    I ran into this same problem and what it turned out to be was that the seat in the carb was not clearing the carb casing. If you look at your seat, the brass needs to stick out past the carb body. I had to remove the gasket from the seat/ fuel inlet and silcone the threads . Hope this works:idea:
  20. meatwad

    meatwad Member

    I had the same problem. Mine was the fuel tickler button. If the gas comes out real fast that could be it. Sometimes it leaks othertimes it doesn't. I just quicky tapped on it with my finger and it stopped.