whats going on???

Discussion in '2-Stroke Engines' started by blue 48, Jan 21, 2012.

  1. blue 48

    blue 48 Member

    had to fix a mates scooter today,he couldnt get it running it turned out i had to block the carb to essentialy choke it . to get fuel to it.
    it runs nice except it wont rev it bogs at wot. is this possibly lack of fuel at top end or somthing else . it has a fuel pump of sorts as well could that be the problem.

    please help, this poor bloke just cracked the head on his only mode of transport and he now needs his old scooter back on the road:shout:

  2. motorpsycho

    motorpsycho Active Member

    it's too lean, you have an air leak probably at the intake tube cylinder gasket or where the carb is connected to the intake tube.
    it's getting too much air.
    Think about it....if you have to cover the carb throat to start the engine, it's getting air from somewhere other than from the carb throat (because your hand is covering it).

    a bog is a sure sign of it being too lean.
    it will have decent power when it's running because a leaner air-fuel ratio will produce more power.
    But if the mix is too lean, you will get the bogging at w.o.t., engine not wanting to rev, and hard starting problems.
    A lean running engine will run to ohot, and eventually cause damage to the pistion and cylinder.

    get yourself a can of starting fluid and get the engine running. Now spray a tiny amount at the connection between the intake tube and the cylinder. if the rpms increase, you found your leak, try not to spray a bunch at once because the fumes can get sucked into the back of the carb which will make the rpms go up (which will throw you off the trail of finding the leak) try to concentrate on one small area at a time when spraying starting fluid.
    Last edited: Jan 21, 2012
  3. blue 48

    blue 48 Member

    ok i understand, its a vmoto milan 50cc for what its worth.
    once it started it fired first push of the starter there on after.

    it goes ok till 30 kmh its a rubber manifold so ill do that.
    it has been dropped and never started till i got it running yesterday. thanks for the advise psyco. :)
  4. Big Red

    Big Red Active Member

    Air leak

    Moto is probably right, but check the fuel level also. If the bowl is only getting enough to idle but runs low (or out) at wot it would bog then also. Get off the throttle long enough for the bowl to fill again and it will run fine, For a second, till the bowl runs out again. Make sure the carb inlet valve is not obstructed. An obstruction could let enough fuel by to run but not enough for wot. Also make sure the float is not stuck in a high position. Sometimes they do just STICK. And, Of course, check that fuel pump. Most pumps either work or not work at all, nothing in between. BUT, every once in a while a pump will just get weak before it takes a total dive.
    Either way, I think Moto is right about it running lean. and you should check for air leaks FIRST anyway. I hope it is that simple so you can get that thing on the road.
    Shiney Side Up,
    Big Red.
  5. blue 48

    blue 48 Member

    thanks guys that helps heaps ill keep you posted :)
  6. HeadSmess

    HeadSmess Well-Known Member

    i think you answered it yourself at the beginning. it has a fuel pump.

    check that for fuel flow first! if its mechanical...work it out yourself! if its a standard "pulse feed" then you are in luck! get the pulse line, and quickly (gently) suck and blow on it. (ewwwwgh!!!! :p) hopefully you thought to take the fuel line off the outlet side, in which case you should be getting at least a squirt with every blow.

    then if it is the pump... theyre fairly easy to come by...and cheap. from the right places!

    and theeen! what type of carby is it? diaphgram butterfly or slide?
    Last edited: Jan 23, 2012
  7. blue 48

    blue 48 Member

    @ headsmess its a mikuni slide type, pump works fine

    after more research, it turns out that owners of the same model say that after a few months of no being used the wont go above 30 when they first use it again. :thinking:

    so all it took was to remove the carb, open it up and clean the jets, float valve and bowl. it was all gummed up. it runs beutifully now.

    thanks for the help folks you guys rock:D
  8. Big Red

    Big Red Active Member


    Thats kinda what it sounded like to me. Like I said, Check for obstructions in the carb. Of course that would include "gummed up" and old stuff in the carb. Sometimes just running fresh fuel through it will flush it out, sometimes not.
    Anyway, glad you figured it out. Now if I could only find a clutch puller for the 1979 motobecane I'm working on.
    Shiney Side Up,
    Big Red.
  9. blue 48

    blue 48 Member

    good luck red im sure youll work it out.
    my friend is happy now he can go back to work.
    or even get to the shops without catching a bus now