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V-Twin Sync Problem

Discussion in 'Maintenance and Servicing' started by gre03, Dec 5, 2015.

  1. Hi All,
    So i decided to have a crack at synchronizing my carbies on my Honda Spada. i made up a manometer jig and put 2 stroke oil in it, hooked it up and started the bike.
    instantly the bike started drinking all the oil through the rear intake. I'm petrified (hand shaking while i'm typing this) of messing it up and destroying the engine. any ideas?
    Should I turn the front sync screw in until the vacuums equalise?


  2. So you've sucked oil into one cylinder. It is unlikely you have hydraulic lock which probably means you haven't really done any damage and may just run a bit smoky for a while, until you burn off the oil.

    If you are worried, remove the spark plugs, turn the bike upside down and shake.

    If you sucked oil in that fast it means either your carbs are WAY out of sync or more probably you used two short a lenth of tube in your manometer. Use longer tube and even if the oil does start heading into the bike, you should have enough time to switch off before it gets there. Then make a preliminary adjustment towards synchronised and try again. As you approach synchronised, the levels will tend closer towards equal and it won't suck into one cylinder as much.

    Have you also got your timing and valve clearances spot on? Otherwise you are possibly wasting your time trying to sync,

    BTW. Some people use petrol so if it sucks in it doesn't matter so much. I don't really see the need and use transmission fluid cos it looks pretty.
    • Informative Informative x 2
  3. Don't Panic you are unlikely to have done any damage with the small amount of oil involved. The oil will be pulled through and burnt. You may need some carby cleaner.

    The sealed end of your manometer tube probably isn't. If air is let in to the sealed end it will just keep pulling your indicator fluid through. So find that leak and fix it first.
  4. As previously stated, 2-stroke oil wont damage your engine.

    Use longer hose and/or get an inline hose connector that can act as a restrictor
  5. Try this type of manometer make up. It won't such up any oil no matter how far out they are.

    Attached Files:

  6. I have 2 bikes, a triple that needs a vacuum gadget to sink multiple carbs and a Ducati that ,well here is the story. I was chasing poor power off idle for a year or so. I was using the professionally bought vacuum gauge to sink the carbs at idle with the idle screws and just above using the cable adjusters on the Ducati also with the gauge. It idled fine but was down on pull from what I remembered from the past till it got to over 1/4 throttle or where the slide cutaway governs the mix. After way way to much fing around I went to the dino. Jetting was fine BUT they found the sink was a good 5mm out. They did it by pulling one carb and putting them next to each other and doing it by eye resulted in much much better acceleration and sink .Made no sense to me but thats what was done and its fine now excelotation wise. So I use the gauge for adjusting the screws but the cables I now do by eye.
  7. I just got back from a nervous test ride.
    First and foremost, thank you to everyone who replied, there's always amazing support from the NR members.

    So after somewhat freaking out, the bike had drunk enough 2stroke oil to bring the levels to a manageable level on the manometer. As i thought it takes tiny, like really tiny adjustments to change the sync. the fluid was probably a few mm out of each other (i'll post up a pic soon of the jig).
    This has fixed the 'misfiring' (?) cylinder where it would periodically just not fire on one of the cylinders when at idle.

    however the 'down' side to this is that the bike feels smoother but less powerful. i suppose when they were out of sync, acceleration would be jerky and hence it felt fast, but now with a smoother engine it feels less jerky and somewhat slower??

    The main thing is the bike still runs. Again thanks for the support :)
    • Like Like x 1
  8. You don't need anything like that much liquid. Just a little above where the tube came back together would have been enough. This would have put the oil further away from the carbs and would have given you more time to switch off if it started rapidly moving towards them. What you are looking to achieve is an equaling of height of the fluid or at least that the columns stop moving. Easier to see in the vertical part of the tube.
    • Agree Agree x 1
  9. Go to your local aquarium. there you can buy some cheap plasic needle valves put them in you tube. close them and once the bike has started slowly open them until you are getting a little movement in the liquid but not som much as it pulls through or is dancing around so much you cant get a reading.

    BTW you can do 4 cylinder bikes with this setup. you do 1-2, then 3-4 then the screw between 2-3.
  10. If you use the bottle method from above no oil is sucked into the carburetors. The worst case is it will all end up in one of the bottles. When you get the carbs back it will be sucked back to the other bottle. adjust until both bottles become stable with some oil in both. The little taps are a good idea even for the bottle method. If you don't open them fully that will slow down the movement of oil and make the whole thing more stable. The bottle method is already more stable and readable than a just a tube filled with oil.