This isn't about how to do it, more about the options out there to assist your ear.
The $2 manometer.
Glenn Radford wrote:A sealed jar with 2 vacuum hoses. One hose has a small plastic bag attached. It is a method of "visually" adjusting the balancing of the carbs once the idle has been correctly set. Attach the hoses to the vacuum ports, the shape of the bag is the "set" point for beginning. Usually not shrunken or too firm. The aim is to retain this initial shape through the rev range. Any change can be corrected by adjusting either throttle cable.
A $4 synchroniser.
Careful, if this one falls into the right hands, it may be used for something else!
Very cool SteveD. The first, third, and the twinmax pics appear to be a differential vacuum gages, something I've wanted but never pursued over the years.
The first one, the one with the bag, is homemade, low tech, and I'll bet it works pretty good. Is the bag inflating or deflating? I reckon that some kind of valve would need to be put into one of the tubes to slow the bag inflation and deflation so you could actually see it happening.
The Third one, with the pretty blue colored liquid tells you which side has more vacuum (oxymoron?). But it looks to me like it would potentially have a problem. A wildly differential vacuum would pull the water to one side. Of course with the liquid level at the right height and the tubes going down into the liquid long enough, then the connecting "siphon" tube wouldn't loose its prime. Still it looks fiddly to set up before use. Maybe not. Maybe blowing into one tube will prime the siphon. And the ends of both tubes open to the atmosphere shouldn't hurt either.
The Twinmax got my attention, but the price cooled it back down. Pushing $100 from what I saw. It's not just the money. It's also having to admit (if only to myself) incompetence in tuning airhead carbs by ear.
Currently I'm using the twin dial gauges. But I'm never confident that looking from one gauge to another really tells me the truth about what's going on vacuum wise. The meters are cheap and I reckon not all that precise compared one to the other. Plus, even if they are perfectly matching meters, am I good enough to compare the dial needle positions to each other? I think I am, but it bugs me having to mark one position in my mind while I go to the other gauge to compare.
In the limit I'm relatively comfortable syncing the carbs by ear, but I would prefer not having to interpret my audible inputs.
I am inspired by this post. I have an old vacuum gauge with the glass broken out that I bought when I was a pup. All I would really have to do is to put that gauge into a glass jar and then bring the gauge line out through the lid without leaks. Similarly I would then have to connect a second hose to a spigot that just goes to the lid. Presto! A differential vacuum gauge. Note where the needle is at rest and then fiddle with the carbs until you get the needle back there.
Thanks for the post. It got my brain working this morning (well, helped by too much coffee). I just hope my brain is working as good as it feels like it is.
Ken
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There's no such thing as too many airheads
Using a manometer is an intriguing idea, since I have a couple. How did you make an access to a vacuum port, did you modify the boot between the carb and head???
1974 R90/6 built 9/73
1987 BMW K75S
1994 BMW R1100RS
1964 T100SR Triumph
1986 Honda XL600R
Hello Jagarra,
Many Bings have a port right under the butterfly and close to the idle mixture screw. This brass port is sealed by a screw.
Older one have the port near the butterfly pivot. Sealed by a screw also IRC.
One of the most precise and easy to make manometer involve buying a board around 1m20 long, crystal plastic tubing and jumpers used to attach electrical cables on a panel.
Put the tube on the wood panel, making a U and attach it to the wood. Pour colored liquid in the tubing (I use permanent anti-freeze for cars which is a red fluorescent liquid) and plug the two tube's end onto the carbs vacuum ports.
Imbalance is easy to see because the two liquid columns will reach different height on the panel. Perfect balance is also easy to spot as the two columns are very close to each other.
If you're rich, Motion Pro sell carb synchronizer based on this principle, filled with mercury but for four cylinders engines. Mercury has the advantage of making the instrument more compact as the density of the "liquid" is greater than the one of the anti-freeze.
Anti freeze is safe if swallowed by a small amount by the engine.... If the engine swallow it, your board is not long enough.
As I own quite precise Boëhm dial gauges, I can tell you that an R65 produce .1 to .2 bar vacuum at idle and goes up to .5 when throttle suddenly opens.
I put it on the bike and gave it a whirl, it seems to be easy to use and I think that it works properly. The gauge mode gives you the possibility of seeing the numbers, comparing the pull of one cylinder against the other, which is easier to get to than with mercury gauges. Seeing the free play on the throttle cables seems to be a bit easier than with my 1984 set of mercury filled gauges.
Other advantages might be the ability to stap the Harmoniser onto the tank bag and see what happens in the real world, it also has a tacho function and an LED light for reading in your tent at night!
Charles
Replica 1070 R90/S (based on 82 RT)
1975 R90/6
The great advantage of the TwinMax is its ability to be used while riding the bike. On something extremely sensitive to balance (like R1100's) this is a very nice feature. That might be of some use in racing, as well.
The Carbtune has many advantages: it shows an actual measurement in cm of mercury (the Twinmax only shows a comparative non-quantified measurement) so it is a useful vacuum gauge for more than just balancing carbs, no batteries to die or leak, it's really sturdy, it has no liquid, it can't get out of adjustment (as gauges do with time), and you can use it on bikes with up to 4 cylinders. Because of the weakness of the Pound, it's even pretty affordable right now. Because of that, I think it's the best way to go for most people (if you want something better than the homemade jobs). If you want to just do it by ear, then you don't need any of this stuff.
If I ever get rid of my Oilhead, I'll also get rid of the TwinMax. The Carbtune is a tool I'll keep for life.
Edit: the Harmonizer looks to be a MUCH smarter replacement for a TwinMax. I think I would choose it over a TwinMax today, but almost all the advantages of the Carbtune still apply when compared to the Harmonizer except that the Harmonizer can also give an actual quantitative measurement - albeit only when measuring a single source, not while balancing two. If the Harmonizer comes out in a 4 cylinder model, choosing between it and a Carbtune would be a matter of taste: higher precision and more information vs. virtually indestructible simplicity.
I have one of these. Got it years a go to set the six butterflies on a fool injected Triumph sports car.(It was a Lucas System)
On the airheads I use the Carbmate to set the balance of the carbs at tickover with the butterflies on their stop, then use the Synchrometer to balance flow with the throttle open.
I have two Colourtune plugs and had a try to see if they were any good for setting balance above tickover, but I couldnt see any advantage using them on a reasonably in tune motor, although they might be useful if I was chasing a hard to find fault.
There was another manometer system around which had a small ball bearing being sucked around a loop in a in a length of clear plastic tube, but I haven't seen much of them for a while.
Adelaide, Oz. 77 R75/7. 86 R80 G/S PD, 93 R100 GS, 70 BSA B44 VS ,BMW F650 Classic
