Vacuum tap

[BrianG]

Alright guys......

Here I sit with a borrowed carb-stick and I cannot find a vacuum tap in the throttle bodies, to attach it to.

 

There are many posts here about carb-stick sync-ing...... so, what's the trick????

[Guest ratchethack]

Brian, the stock V11 manifold spigots have brass barbs between the TBs and heads on the outboard sides, up almost to the fins. They point outward and slightly down. If you don't have them, a PO must've replaced them with plugs. I'd get the OEM ones back in there so I could use my carb-stick if I were you.

 

BAA, TJM & YMMV

[BrianG]

OK.. I found the blanking plugs that the PO put in there.

 

Of course nobody up here has metric threaded hose barb fittings and the Guzzi dealer has no parts in stock!

 

So I had to spin some 1/4" pipe thread units down on the lathe and thread them myself. Seemed to work out OK.

 

Now I can use the carb-stik

 

Now.... what is supposed to happen with them when I'm done? Are they supposed to be joined together as some kind of balance tube?

[dlaing]

OK.. I found the blanking plugs that the PO put in there.

 

Of course nobody up here has metric threaded hose barb fittings and the Guzzi dealer has no parts in stock!

 

So I had to spin some 1/4" pipe thread units down on the lathe and thread them myself. Seemed to work out OK.

 

Now I can use the carb-stik

 

Now.... what is supposed to happen with them when I'm done? Are they supposed to be joined together as some kind of balance tube?

That is what I do. Technically it may create turbulence, but I am not worried about it until someone proves it to be a problem.

Some cap them off with rubber caps, but the caps can blow off from a mild backfire.

You can also put a balance tube on but seal it so it does not balance. It may blow off, but at least it will dangle and you can reattach it if you notice it blew off.

[Ryland3210]

FWIW, my 1970 Norton had a balance tube between its carbs, stock. Ran fine that way for decades.

[BrianG]

That is what I do. Technically it may create turbulence, but I am not worried about it until someone proves it to be a problem.

Some cap them off with rubber caps, but the caps can blow off from a mild backfire.

You can also put a balance tube on but seal it so it does not balance. It may blow off, but at least it will dangle and you can reattach it if you notice it blew off.

 

So, we don't want a balance tube? Why not?

 

 

 

FWIW, my 1970 Norton had a balance tube between its carbs, stock. Ran fine that way for decades.

Ryland, my Norton had it as well.

[Skeeve]

So, we don't want a balance tube? Why not?

 

Nix, nix! You want the balance tube, just keep it small so it doesn't actually flow a significant amount of air: it's really just to even out the vacuum across the cylinders. Yamaha actually patented(?) this whole idea back in the 80s, called it "YICS" or somesuch. Required a special tool to blank off the passage so that the individual cylinders could be balanced.

 

Use the balance tube, it seems to work well.

[Guest ratchethack]

Gents!

 

Lest we get so far off the fairway and so far past the rough and over the dale and through the woods that we find ourselves mired in the proverbial Evil Swamp of Frivolous Thrashing. . .

 

The orifices in the stock barbs are .038". This is approx. the diameter of a straight pin. This WILL NOT allow enough air flow to either blow vacuum caps OR a cross-tube off in the event of a backfire (unless a C-4 charge were to've made its way in there and somehow detonated itself -- in which case you've got more important things to worry about than a vacuum leak! ), NOR will it allow enough air flow to "create turbulence" when connected via a cross-tube, NOR will it allow enough air flow to act as an effective "balance tube" between the TBs.

 

These fantasies are merely more of the garden variety fleeting feathers of foofery and folly borne of wild, unchained speculation demons clogging up the flow of productive enterprise (again). Increased thread protection measures are occasionally required lately.

 

Any more of the same and I'll hafta break out the "Whack-a-Mole!" Thread Protection/cloaking device. . .

 

The silly stock vacuum barbs were put in there to provide low-flow air circulation through the charcoal canisters for recovery of aromatic petrochem-baddies from gas fumes. Back in the days when Norton Commandos were created to roam the Earth, and the hysterical dread of Global Cooling threatened life as we knew it, there was (blessedly, and rightfully) little of the current berserk levels of hysteria about fouling our air to the point of asphyxiation, causing the ozone hole (remember that crisis? ) to grow to the size of the Pacific Ocean, allowing cosmic rays of the sun to zap our chromosomes, causing our kids to be born with dinosaur heads, and melting the polar caps via today's hysterical dread of Global Warming that threatens life as we NOW know it, so baby polar bears will have to swim their entire sad, short fuzzy little lives until they drown because very soon there'll be no icebergs left for them to play on. . .

 

So they are VERY VERY IMPORTANT THINGS, these tiny little holes.

 

But they also happen to be the just right size to work very well with a carb sync device to balance the TBs.

 

I use a vinyl tube manometer from the local hardware and cap 'em with vacuum caps. Works like a Champ.

 

Does that clear things up?

 

Carry on!

 

Cdr. Hatch Scratchjacket, G.Ph.D., Esq., BAA, TJM & YMMV

[Ryland3210]

..

Ryland, my Norton had it as well.

 

If the Japanese actually patented the balance tube concept in the 80's, the patent would have easily been invalidated by a reference to Norton (mine was a 1970). In fact, if they left that off the references in the application, shame on them.

 

The passage through the Norton's balancing tube was quite large. I believe large enough to help deliver more balanced flow to both cylinders at idle, if the carbs were not ideally balanced. For synchronizing, one could separate these and attach mercury manometers ("sticks" in the current jargon) to each. When finished, reattach the balancing tube for compensation for the Amal carb variation with wear.

 

It used to amaze me how much the engine would vibrate in the Isolastic Suspension, while somehow the Amals did not seem to be affected. Loved the zero vibration in the handlebars despite the rigidly mounting at anything above 1800 RPM-the opposite of my Guzzi. Ah well, can't have everything!

[Mr. Average]

I have been busily learning my first Guzzi, a 97 Sport 1100i. I am looking for the access ports to check the vaccum and for the life of me, I don't see them? Any of you wise and learned ones know where they are?

[Skeeve]

If the Japanese actually patented the balance tube concept in the 80's, the patent would have easily been invalidated by a reference to Norton (mine was a 1970). In fact, if they left that off the references in the application, shame on them.

 

IIRC, I think what Yammie was actually patenting was casting the balance tube into the head between multiple parallel cylinders, not the actual balance tube idea itself. Not that it's important, just to clarify my earlier statement...

[jrt]

OK.. I found the blanking plugs that the PO put in there.

 

 

They may have come that way from the factory. Mind did and I'm the original owner.

 

I added barbed hose adapters and a small hose and the Guzzi didn't mind a bit.