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Carb Sync Tool Review
#816680 07/18/20 9:05 pm
Joined: Mar 2012
Posts: 225
Likes: 2
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Greetings forum members.
Recently Morgan, (our forum administrator) was looking for volunteers to test a new carburetor sync tool. I accepted the offer to test it and post my thoughts on this forum. About a week after accepting the task the tool arrived. I am unclear as to the relationship between Morgan and the tool company, but there was a note in the box that said DigiSync is a new seller on Amazon and they needed all the help they could get. Their website address is thedigisync.com
I have to apologize to Morgan. I am sure he was expecting a prompt response in testing the tool and my posted report. After I received the tool, life got in the way of bike business for me, and the tool sat for almost a month. There was also trouble with picking a suitable bike to test the tool, more on this later.
In the end I chose my 1972 Norton Commando:

[Linked Image from i.postimg.cc]

Any manner of testing the vacuum synchronization of multiple carburetors requires a viable access point to connect the tool to a vacuum port between the engine and the carburetor. I have a few bikes that have multiple carbs, but being vintage British, they don’t have any sort of vacuum port as part of their makeup. I found this to be one very frustrating thing in conducting this test. These bikes were built before an accurate sync tool was considered for motorcycle use. My only bikes that have an access point is the Norton and a 1974 Ducati GT750, and its access is a sealing screw threaded into the intake manifolds, which require a threaded stand pipe, something I don’t have, but now have on order. (I will test it after the stand pipes arrive). I thought the tool would be a great candidate to test my 1971 BSA Rocket Three. It has three carburetors, a little more difficult to sync that a twin, and would play to the strengths of the tool itself. Unfortunately, I recently crashed the Rocket in a high side flip that messed it and me up pretty good. It will not be a candidate for testing this tool anytime soon.
The Norton has a balance tube between the carbs which the British did to smooth out the idle and make tuning easier. I don’t think they thought it would one day be used to connect a modern vacuum synchronization tool. After removing the balance tube, there are ready made access points that the tool easily connected to.

[Linked Image from i.postimg.cc]

The tool itself came in a plastic storage box. This is a nice feature. I am pretty hard on tools as they often scattered and moved around the shop. This plastic case keeps all the pieces along with instructions together. The main tool unit appears to be well made. It is fully digital, there are no fluids or mercury with it so the past problems of evaporation of fluids or the possibility of sucking fluids into your engine are nonexistent. The tool operates on a 9-volt battery, and has an on/off switch. The tool shipped to me came with a 9-volt battery that was completely dead. I’m sure it was packed with the switch on. The tool also came setup for four carb testing or less. It has two blanks; I’m guessing the unit can be set up for up to six carbs as required. Also included was four rubber pipes that interconnect between the carbs and the unit.

[Linked Image from i.postimg.cc]

[Linked Image from i.postimg.cc]

[Linked Image from i.postimg.cc]

The unit and the rubber pipes feature quarter turn quick connects. These are good quality and make a very slick setup. Also included were four rubber caps complete with clamps. These are for sealing off an existing vacuum port on a carb intake manifold, but as I said before, our British bikes aren’t set up for this testing in the first place. This kit is obviously geared for more modern multi cylinder bikes that have a single adjustment screw that would adjust the butterfly valves in the throat of the carb or throttle body. Those of you that adjust your twin carb bikes the old school way, e.g. feeling that the throttle slides lift at exactly the same time and that they idle at the same rate by ear and exhaust tone can probably do a fair job. This tool would be invaluable in tuning 3-4 or more carbs. I look forward to testing it on my triple after I fix its unfortunate mishap.
Make sure the bike is warmed up, connect the rubber pipe to each access point in the intake manifold. Turn on the tool unit, and let it calibrate itself. This took approximately 30 seconds. After the unit is done calibrating it settles on an offset value of 25, which is its representation of normal atmospheric pressure.

[Linked Image from i.postimg.cc]

Start the bike and let it settle to its idle position and observe the tool unit. Each rubber pipe has its own readout. As you can see, my Norton is in very good tune. Both cylinders show the same vacuum value. The value fluctuated slightly, but was never more than one or two points different. The instructions that came with the tool states that any difference in value of less than three points is very acceptable. Any larger differences would require an adjustment of the throttle slide by manipulating the adjustment screws for the throttle slide on the top of the carburetor, or perhaps locating and fixing an air leak around the intake tract. All individual results may vary wildly! It is unclear to me what the value on the readout represents. The goal is to adjust the carb or throttle to be as close to the same as each of the others. The instructions state the unit is capable of accurately measuring pressures and vacuums between 1-12 psi
1.036 to -24.432 inch of mercury (inHg)
68.948 to -827.371 mBar


[Linked Image from i.postimg.cc]

[Linked Image from i.postimg.cc]

Summary: I think the DigiSync tool is a very well made piece of equipment, although our British bikes are not set up for it per se. This was the biggest hassle of producing this post. If you can get past the difficulties of arranging a way to have an access port into the intake stream/vacuum, then this tool is highly recommended. It is very easy to use and I suspect it is highly accurate. My thanks to Morgan for the opportunity to test it and relay my experiences here to the forum. I will test it on the triple, when I get around to the repairs getting it back on the road.
Fullminator

Last edited by Morgan aka Admin; 08/02/20 6:28 am. Reason: Added the thread to the Portal News section
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Re: Carb Sync Tool Review
Fullminator #816700 07/18/20 10:45 pm
Joined: Mar 2006
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So at idle you synch the numbers by the throttle stop screws or by the cable adjusters on the carb top?


1978 Bonneville T140E
1974 Trident
1970 BSA Thunderbolt
1971 Norton Commando
1972 Norton Commando
1973 Norton Commando
1974 Norton Commando
2018 Kawasaki Z900RS


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Re: Carb Sync Tool Review
htown #816732 07/19/20 4:49 am
Joined: Oct 2008
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Originally Posted by htown
So at idle you synch the numbers by the throttle stop screws or by the cable adjusters on the carb top?
Throttle stop screws for idle, cable adjustment for higher throttle setting.
BTW: The OIF Triumph and BSA twins also have intake crossover tubes which give available vacuum access. On your triple you would need to have tubes installed in the intake gantry.


Stepping on others doesn't make you stand tall.

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Re: Carb Sync Tool Review
Fullminator #816736 07/19/20 7:37 am
Joined: Jul 2001
Posts: 2,411
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Ride safe today!
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Quote
I am unclear as to the relationship between Morgan and the tool company

BritBike forum was approached by DigiSync snd they asked if we could conduct a test and write a review.
We do not know them previously to the request.
The challenge was accepted by our member Fullminator and the result is this thread.

This is the first time we have been asked to review a product.
It looks like its easy to read more exact in digital figures rather than the old way with a bearing ball that moves from side to side.
Also one can read the exact RPM as it looks on the photos.

You mentioned that there was four connections and two blanks,
That is correct.DigiSync comes in either up to two or four or six connections and they are priced accordingly.

Thanks for the review!
Feel free to come back and add more info when you use it next time.

PS: DigiSync responded to Fulminators remark on the dead battery
Quote
-Regarding the dead battery... We had a batch of units that were packaged with the unit face-down. They jiggle around during shipment and the ON switch is bumped by the hoses. We have already identified and corrected this issue. Looks like Fullminator, unfortunately, got one of these units.

Last edited by Morgan aka Admin; 07/19/20 6:46 pm.

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Re: Carb Sync Tool Review
Fullminator #816756 07/19/20 1:17 pm
Joined: Dec 2009
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Fulminator, your Norton is a stunner!

Re: Carb Sync Tool Review
htown #816783 07/19/20 7:10 pm
Joined: May 2013
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Originally Posted by htown
So at idle you synch the numbers by the throttle stop screws or by the cable adjusters on the carb top?


You should adjust by the carb top screws, I guess there would be no harm using the idle stop screws to set the carbs until you have removed the slack from the cable but ideally you want the synchronisation right through the carb range from tick over to full throttle. The idle stop screws on the carbs become almost
Redundant. If you look at a proper bank of carbs like the rocket 3, these have no idle stop screws. The gantry sets the tick over speed by raising all the slides equally from the carb tops.

Hope this makes sense.


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Re: Carb Sync Tool Review
Fullminator #816837 07/20/20 4:36 pm
Joined: Mar 2012
Posts: 225
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I want to reiterate that I found this DigiSync tool to be a very nice quality item. It was easy to use and I am sure very accurate. The readout does show the RPM of the engine, which I thought could be used to check the accuracy of the Smiths gauges on your bike, at least the tachometer! Other syncing gauges I have used present their own problems. Using mercury with a vacuum presents the danger of sucking mercury into your engine, or others using an alternate water based medium- the stuff will evaporate. Still others with dial gauges or the side to side ball bearings Morgan spoke of can be erratic and difficult to read, and all are highly suspect when it comes to accuracy. This DigiSync tool improves on all of that. No fluids to worry about, and a digital readout that is easy to read.
When setting up your carbs, the first thing to make right is to ensure that the throttle slides are coming down to a stop resting on the idle stop screws and not being held up hanging on the throttle cable. The cable should be slack with the slide sitting on the throttle stop screw. The DigiSync tool would then be used to make sure that all the slides/throttle bodies are at the same position, or same vacuum rate. The next step is to make sure that all the slides lift at exactly the same time and rate. This makes for crisp throttle response takeoff from idle. This is done by adjusting the throttle slide cables at the carb top, making the take-up or slack in the cable the same on all carbs. The slack, when the twist grip is at the closed throttle position, should be just perceptible. Some British bike owners manuals recommend a slack rate of about 1/8". I find this to be a bit too much. I prefer a slack rate of just perceptible only. Getting the cables, and their slack rates and the throttle stop screws positioned all the same is the goal to get identical vacuum rates at all throttle settings. The DigiSync tool can be used to check for identical vacuum rates at many different throttle settings thereby indicating a uniform lift rate throughout the slide/throttle range. The tool itself is made in such a way that these measurements are easy to obtain and read. You can hook up the tool to two, three, or four carbs, leaving the unused ports unconnected-very simple.

To henryanthony: thanks for the compliment on my bike.

Fullminator

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