Carbtune query?

"Vacuum bypass doesn't matter as its a sphere the presented face of the ball bearing is always the same area and the vacuum applied to it is always equal regardless of any bypass."

OK, so there is a pressure gradient from the intake on one carb to the intake on the other. The ball will try to move inside the tube towards the lowest pressure because it has a force acting on it. As it moves in that direction it begins to rise upwards until its weight offsets the pressure differential?

The ball will move towards the the carb with the greatest vacuum. As you adjust it it will either move further away from central if your adjusting it in the wrong direction or back to the center if your adjusting in the right direction. Once the outer ball is directly under the inner ball the vacuum on those two carbs is exactly equal.
I am assuming that in the outer tube under the shrink wrap there is a restrictor of some sort which is of smaller size than the ball as you cant tip the ball out the tube.
Just to add I assume the smaller / lighter the ball the greater the deflection so greater the accuracy.

Whoever invented this was a pretty smart guy but I think I'll stick to pressure gauges.

Me too. Ed

There is nothing wrong with vacuum guages as long as you are certain that all the guages read exactly the same for a given vacuum and Im not advocating anyone uses this over accurate exspensive guages. However, as a simple, effective and inexspensive method this has no comparison.
My original query was regarding the new bar type morgan carbtune and after trying one my results proved, to me, that they are not as accurate as the old mercury type and the new bar type guages, at least on the one I borrowed, was not balanced enough without a lot of trial and error to "adjust" them to give me any confidence.
If you have good quality dial or digital guages already and you are certain they all read the same for a given vacuum then use them. Im not saying relegate them to the back of the workshop. If you have bar type morgan carbtune and have not run a simple test to check they all read the same for a given vacuum then balancing your carbs is a guestimate at best. Just a heads up guys.
I now have neither guages or carbtune after the demise of my original mercury set but I do have one of these and as balancing tools go I've not found anything as simple, 100% accurate and cost effective, making it hard to beat if your shopping for a tool to balance your carbs.

Agreed that it's a very simple setup...I like it, particularly for 2 carb bikes, but it has some drawbacks.

How do you know that your reference carb is set correctly?

How do you know the actual pressure? (KHI has a minimum spec)

Lastly, you can only do one carb at a time. When one carb is adjusted this has an effect on all the others. Do you go back and check the ones already done?

hardrockminer wrote: Lastly, you can only do one carb at a time. When one carb is adjusted this has an effect on all the others. Do you go back and check the ones already done?

I do, but not sure if others would. Although I've never had to re adjust a carb that has already been done. Doing one carb at a time is not a problem. All the mix chamber caps are off, as with any set up, then just pulling off or pushing on a vac caps.
I see the big positive of these is that you are using the same measure tool for all the carbs so dont have to worry about any variances between guage 1 to 4 inclusive or bar 1 to 4 inclusive.

I think the moral of the story here is that whatever you use you need to be confident that your gauge needles or carbtune indicators all read the same for a single carb. If they don't then there is no real point using anything.

Back in the ancient times, Suzuki sold a manometer to dealership mechanics that looked a lot like the mercury style, but had a ball bearing in each tube instead of the liquid death.

That ball bearing setup is interesting. Thanks for sharing.

Spitballing here; If there are four straight, parallel vertical tubes, each of suitable & identical dimensions and each having within them an identical ball bearing perhaps retained with a pilot or other precision orifice for damping & flow control, would that setup not behave essentially the same as mercury sticks?

We feel an experiment coming on...


Good Ridin'
slmjim & Z1BEBE

Thinking about it, all you need to make any tool work is a way of syncing the four gauges/tubes or what ever. I am surprised there is no easy way to adjust the new rod style carbtune. Surely, all you would need is an adjustable inline valve to each gauge. Something simple like they use to regulate the air flow in fish tank aerators. Set all four so they read the same on one carb and away you go.

cant believe for the price of a carbtune they couldn't throw four of these in!
cheap as chips. pack of 4 for £1.75 from your local pet store

Interesting thought on the valve Warren, I may have to try it and see what happens. My guess would be with the restrictor tubes inside the vacuum lines and with the weight of the sliders, Carb Tune probably felt there was no need for the adjustable valves on each hose as the adjusters would just act as an extra damper. Just for grins I installed my Carb Tune on only one cylinder and rotated through all four tubes. The reading on the Carb Tune was the same for all four tubes. Then I stuck my Snap On vacuum gauge on the same port but it went crazy because there is no damper on it. So I may have to make a run to the pet store just to prove this all out. Oh and there is nothing in the Carb Tune manual that talks about calibrating the tool, only about cleaning it and installing the restrictor tubes. I just remembered it's been years since I was in a pet store and that was to buy my youngest son a gerbil about 25 years ago. It died about two months later and is buried in the back yard under a rock. More money down the drain....
Rick H.

I think I would be happier with just valves an no resticter Rick. The valve would then serve both purposes. There is definately some room for design inprovement in the bar type carb tune which would make them much easier to set up and more user friendly.