Stage6 R1200 vs Yasuni C16

Discussion in 'General Tuning' started by leo015, Feb 19, 2014.

  1. turbovetto

    turbovetto Well-Known Member

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    If the depression pump is not stopping the fuel flowing out of the tank and the needle valve is not stopping the bowl filling up when it's full, then the carb is constantly overflowing. Unless it's just a plain old fashioned hose-leak.
     
  2. leo015

    leo015 Member

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    I dont think its a hose leak, because it's leaking directly under the carb. How can i check the needle?
     
  3. turbovetto

    turbovetto Well-Known Member

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    It's the needle valve that is actioned when the floaters rise up. The easiest way to check this is remove the carb - no need to unplug everything - just the airbox, the carb from the admission pipe - and then remove the fuel inlet pipe and the bowl. Put a bit of tube (air tight) on the inlet of the carb, blow - and then action the floats (move them up - like they would go up if the bowl was full). The needle valve should stop the air you blow in. Sucking is a more effective test but blow first so you don't get a gob full of petrol vapour. It should make an air-tight seal and stop the air passing.
    Somehow I think you will find that it works fine and that your leak is just the bowl (again). A leaky needle valve - it happens. A leaky stopcock - very rare - usually they don't let enough petrol out. Both at the same time ? Unlikely.
     
  4. leo015

    leo015 Member

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    But how is it possible that it still leaks after it's shut off?
     
  5. leo015

    leo015 Member

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    Note that i started the bike for like 15-20 secs and switched it off.
     
  6. turbovetto

    turbovetto Well-Known Member

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    Gravity -
    your depression pump (if you still have one) is obviously not stopping the fuel from the petrol tank - and your needle valve isn't stopping the petrol filling the carb either. Carb gets full, carb overflows. Did you doctor your depression pump to just let fuel out ? If so - or of there is no depression pump - you need a tap.
     
  7. leo015

    leo015 Member

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    I have no idea about the depression pump. Where can i find it to check?
     
  8. turbovetto

    turbovetto Well-Known Member

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    it's the thing poking out of the fuel tank with the two hoses attached.
     
  9. leo015

    leo015 Member

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    Well i have a hose that's hanging out of the scoot but it's not leaking from there. It's damp and wet only at the bottom of the bowl, as the video showed. Nowhere else.

    Also, what's that golden screw on the side? I've seen it on my carb but don't know what it does.
    [​IMG]
     
  10. turbovetto

    turbovetto Well-Known Member

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    that there is your richness screw. it has the same function as an air screw on a normal carb, controlling the first part of the acceleration process, but instead of metering the air going into the slow circuit, it meters the amount of fuel going into the slow circuit. so you tighten to make it poorer and loosen to make it richer. Like an air screw it's usually done up all the way and then loosened about one turn and a quarter.
     
  11. leo015

    leo015 Member

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    Hmm, so any idea about the leak?
     
  12. turbovetto

    turbovetto Well-Known Member

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    If you disconnect the petrol hose from the carb - does it piss petrol ?
     
  13. leo015

    leo015 Member

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    I'll have to check tomorrow as it's really late now. I'm seriously thinking about buying a new carb, the whole situation is very frustrating. I just came home and it was acting very weird, like the fuel flow was stopping for a second and then continuing again. By the way i did a race with another Beta LC with Malossi MHR Rep, MHR Team 2 exhaust and won him for 5-6 meters or even more hehe :D
     
  14. andy-pp

    andy-pp Member

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    absolutely spot on :)

    A problem with highly tuned variator bikes that are going to be used on the road is that despite the variator you do still actually need a fairly wide powerband otherwise once the variator is fully open the only way for the speed to then continue to increase is for the revs to increase also, so if you have a peaky narrow powerband exhaust although it may have a higher peak on paper a slightly lower power exhaust with a broader band can often beat it if set up properly because the wider powerband can be utilised better on 'over-run' after the variator has maxed out.
    An R1200 permanently runs at very high revs but really doesn't work well on the road (designed for full throttle racing, not stop/ starting in traffic and has no power at lower revs) and really needs to be set up on a dyno to get the best out of it. A C16 is a much better choice for that kit and makes for a very fun bike.
    If you cut up a quality exhaust like a mid level Yasuni you can see they've done something really clever to get both high peak power and a wider over-run powerband.
    In the front section there is an additional cone welded inside with holes drilled into it.
    [​IMG]
    At a certain rpm/ exhaust velocity the gases start to pass through the holes which effectively means the cone has changed size and the exhaust now has a different powerband.
    This is effectively like have a powervalve fitted (not really necessary on a standard bike because of the variator) and it means that the powerband is now much broader. The cost of this is that you loose a tiny bit off the peak power.
    You can see this here...
    http://www.pedparts.co.uk/c/asset/sports-pipe-blog/50cc.png
    if you look at the leo vince pipes they have a narrow power band but a high peak power- the yasuni R pipe with the internal cone makes a far wider powerband and *also* revs far higher because of the internal cone. You can also see the peak is flattened off very slightly compared to the other pipes but this is a small price to pay given that tuned auto engines spend a lot of time past peak power rpm once the variator is maxed out
     
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  15. leo015

    leo015 Member

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    Very interesting and helpful for me to understand mate, thanks a lot! Do you have an idea about the leaking?
     
  16. andy-pp

    andy-pp Member

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    did you do everything turbovetto suggested? if you follow what he said carefully that should isolate the problem for you
    also check for sure that it isn't leaking from where the hose attaches to the carb- make sure it is on there tight-
    if you get really stuck take the carb off and attach a fuel line to it on the bench to see exactly where the leak is coming from- you can then take off the float bowl and push the float up with your finger to see if the valve is passing etc.
     
  17. leo015

    leo015 Member

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    When i'm driving also it feels like the fuel supply is being cut for half or a second and then continuing. Could that be a clue? And what does it mean?
     
  18. andy-pp

    andy-pp Member

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    i can only suggest that you follow
    i can only suggest again that you follow exactly what's already been suggested ;)
     

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