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Carby Synchronisation question (poss with 1 vac gauge?)

Discussion in 'Technical and Troubleshooting Torque' started by RGVroomDaddy, Dec 30, 2005.

  1. I have a zxr250a and would like to have a go at synchronising the carbs.

    I have seen you can get dedicated 4 bar mercury gauges for quad carbs like this but was wondering if anyone has tried it using tee junctions and a single conventional vacuum gauge.

    I can't see why with a bit of patience it shouldn’t be reasonably accurate, you basically just do one at a time and have the tee in all four vacuum hoses with a stopper on each and just move the gauge from carb to carb removing the stopper and replacing each time you move it.

    It might take a couple of runs through each carb to get it right but saves spending hundreds on the gauge that will only get used a few times ...

    Alternatively, there is a slab in it for anyone in Northern suburbs Melb who wants to lend me a proper gauge for the day :!:

    Also, on this topic does anyone actually have this model bike and has done a carby sync? I have a pdf manual for the zxr250c but it is not exactly the same and apart from that the manual scan is completely fubar, looks like it was scanned from a photocopy on a really crap copier and all the diagrams are virtually unreadable (i.e. almost black!)

    Anyway, the carbs have four hex screws with a little plastic shrouds around each one and I figure these are for the sync adjustment but was wondering if anyone could confirm this or better still if anyone has a manual for the A model zx2r ... I have done extensive google and the one that pops up is always the C variant.

    FWIW The bike actually runs pretty well, it had a bodgy air filter when I got it so carbys well a bit clogged low rpm running rough but after a bottle of nulon total fuel system cleaner through the tank and half a can of throttle body and carby cleaner in the carbs when I put a unifilter in it, it now idles pretty smoothly and runs well at low revs but is still not perfectly smooth and I think I could get it a bit better with a sync.


  2. Buy the 4 guage manometer and you will not regret it.. :wink:

    Your idea sounds good, but its a lot of messing around. I wouldn't use a T thou, I'd replug it into each vacuum hose leading out from the throttle for more accuracy.

    If you really don't want to fork out the money to buy one, pay someone to do it for you.

    You can also use the same manometer to adjust efi throttle bodies as well has carbies.

    Mercury guages are cheap, around $150 and are more accurate than the than the float types, buy you have to be extra careful not to suck in the mercury.. or bye bye engine bearings!
  3. I assumed the gauge regardless of single or 4 gauge would have to be teed in to keep vacuum to the carbys otheriwse it wouldn't run ... the manual is pretty vague about the procedure it just says "attach suitable vacuum gauge to the pipes on the carby holder" I just assumed they would be teed in but is this not the case?

    I am inclined to do the work myslef (always did on my turbo car including engine rebuild) but how much would I expect to pay for a carby sync? Any recommendations in for honest non bodgy shop in Northern suburbs Melb or CBD?

    Also, how do you stop mercury being sucked in??

    Thanks for help so far!

  4. Did a bit of a search for gauges on the net ... can get Morgan Carbtune http://www.carbtune.com/ for about A$130 shipped for the UK. Any other suggestions? It uses metal rods not mercury but the iste does a pretty good sales pitch and has heaps of info, FAQ etc.

  5. I used to balance the carbs on my bikes. It's a fiddly job and unless you get quality guages it makes it difficult to get it spot on.

    I used to get mine calibrated at work. They were forever going out of calibration. Ended up spending the money and getting our local whiz, Glenn Middlemiss, to do it. Thing is, there's not much really to go out of sync on them. All you're doing is to ensure that each carby has an equal throttle opening based on manifold vacuum at specific speeds.

    And yeah, you need one per cylinder. Because as you adjust one, the others change. Swapping between the carbs would mean that you'd be chasing your tail, if you used a single gauge.

    Perhaps you'd like to have a go at making a set of manometer based ones. Use water instead of mercury, maybe? I'm sure that there would be plenty of sites out there on how to do this. All you'd need is a length of clear tubing, some crimping clamps to help dampen the pulses and the fittings to connect onto the manifolds.
  6. Vacuum, or rather, atmospheric pressure has the ability to push fluids uphill. For example, for every metre you need roughly 10 kpa of pressure.

    In the case of vaccum gauges, you'd work out what the pressure is at the carbies. Work in an absolute figure. Instead of say, - 50 kpa, work with 50 kpa abs. -90 kpa is 10 kpa abs.

    You'd then set up the hoses so that they loop up and over. Work out the height from the top of the manifold to the top of the loop that you need to stop the carby sucking the fluid up and over.

    Install small needle valves on each of the pipes. Start the engine with them closed and open them slightly til you see a response in the fluid column. They are throttled to dampen the pulses that each induction stroke causes. This helps for more accurate readings. If the column is "sucked" up too high, close the valve in till it stops and reposition your hoses.
  7. i have vacuum guages.. happy to show u how
  8. Yep you need 4 gauges. It would be more than a couple of passed and unless you can see what the current adjustment is doing to all cylinders you would be just chasing your tail.

    Also the sync screws won't be on the carby bodies themselves. rather they are in the throttle linkages between cyclinders. There will be 3 relative adjusters and one all adjust (your idle adjust screw).

    I got a set of 4 vacuum gauges for $90 from MCAS and I wouldn't much around for less.
  9. Thanks for all the tech suggestions everyone and thanks for offer of help Androo but I have ordered a carbtune off the net since it is not that expensive.