Digi Sync Users - Question on Tach

[Harryc]

So I got a Digi Sync recently and finally got a chance to use it today. It worked fine, but one thing I noticed right away is that the tach on the Digi Sync read 200 to 300rpm or so (by eye) higher than the Tach on the Valk. Which one is more accurate?

[The emperor has no clothes]

As I understood it, the DigiSynch was more accurate. I think it calculates it based on vacuum pulses. Pretty easy to use, wasn't it ? 

[Harryc]

As I understood it, the DigiSynch was more accurate. I think it calculates it based on vacuum pulses. Pretty easy to use, wasn't it ? 

It was awesome my friend. The bike runs much smother. A bit more power and another plus that is more subtle and only detected by ear. Before when I shifted up and gradually applied throttle I could hear individual carbs/cylinders kick in/fire first. That phenomena is gone.

[oldsmokey]

Mine was recently purchased and matches very very close to the bike tach.

[Harryc]

Mine was recently purchased and matches very very close to the bike tach.

That's interesting. I wonder what I should be looking into? The bike is a Tourer that was recently Redeye Shiny kit desmog'd. Cutoff valves or lines on the carbs? New/replacement Digi Sync? I can't imagine I have a vacuum leak elsewhere, but I did not check the cutoff valves or replace those lines. Carbs were recently rebuilt as well.

[Steel cowboy]

Harry how young are the o rings between the manifold's and the heads.

[Harryc]

Harry how young are the o rings between the manifold's and the heads.

Thanks for the reply. They are brand new within the last 6 months.  I may be chasing a shadow here, the bike runs great, but I paid good money for the Digi Sync so I'd like to know why it may not be matching the bikes RPMs.  Anyone with a Digi Sync willing to test it? I'll pay postage both ways and buy you a beer next time we meet. That or I'll just go back to the seller and ask for the same...maybe that's the best idea.

[sdv003]

I had the same phenomenon.  Digisync showed 900 rpm, tach was 700 or so.  Idles very nicely at that speed, so I didnt see a reason to go any farther with it.

[oldsmokey]

Might want to compare with a wired or wireless digital tach. When I say it was close, according to memory , it was +- 25 to bikes tach. Did not compare to a third source.

[Harryc]

I had the same phenomenon.  Digisync showed 900 rpm, tach was 700 or so.  Idles very nicely at that speed, so I didnt see a reason to go any farther with it.

Thanks, same here. Idles and runs great.  @oldsmokey, good idea and I do have an old wired Tach I might fool around with.  Meanwhile I did email the seller so we'll see if he has any suggestions.

[Hook#3287]

Harry, I don't remember it being an issue, so I guessing my was DigiSync was close to the OEM tach.

As I'm sure you know, that doesn't affect the DigiSyncs accuracy.

BonS is a good guy and I'll bet he'll do what he can to help you out.

[Harryc]

Thanks Bill. So I took a look around and what I have on hand is an old Sears Engine Analyzer with a tachometer. It has (3) connections, (2) for the battery and (1) for a coil connection. It has 4, 6, and 8 cylinder settings. Is this something I could use on the Valk and if so where do I hook the coil input to get a signal?

[Hook#3287]

Thanks Bill. So I took a look around and what I have on hand is an old Sears Engine Analyzer with a tachometer. It has (3) connections, (2) for the battery and (1) for a coil connection. It has 4, 6, and 8 cylinder settings. Is this something I could use on the Valk and if so where do I hook the coil input to get a signal?

You're asking above my pay grade, but, I believe the coils fire both spark plugs they are attached to at the same time.  So the answer is a 3 cylinder?

I definitely could be wrong on this, me and electrical stuff never got along.

[Harryc]

Thanks. I did hear back from Bon S and he doubts the Digi Sync is defective but will work with me. Meanwhile he did say the Digi sync doesn't care if you have one or six channels hooked up to display the correct RPM. I may try just one channel and try it at a few carbs to see if the issue is related to just one carb.

[indybobm]

Ok, now I'm curious. If it does not care if you have one or six hooked up, what is it monitoring to compute the RPM? By the way, I have an early Digi-Sync that I sent back to Bon to have the tach function added. has always worked perfectly. The tach is correct also.

[Harryc]

Ok, now I'm curious. If it does not care if you have one or six hooked up, what is it monitoring to compute the RPM? By the way, I have an early Digi-Sync that I sent back to Bon to have the tach function added. has always worked perfectly. The tach is correct also.

My understanding is it monitors vacuum pulses. Here's what he said "It doesn't matter to the Digi Sync how many channels are in use so you might just try one channel and see if there's any difference. Just a thought as I don't expect any different result." If you think about it this makes sense because the Digi Sync can also be used to sync (2) carb bikes with (4) unused channels, or (4) carb bikes with (2) unused channels, etc. So it knows how many channels are hooked up, but I have no idea what algorithm it uses to calculate rpm from them if that is what you are asking. I'm guessing Bon S might know but I did not ask. A good guess might be it counts the pulses p/second from each active channel, averages them, then uses an Algorithm to convert that number to rpm. A good question in general might be if that is the case, is it possible to have one or 2 carbs not pulse the same as the others thus throwing off the calculation. I don't know enough about the internal workings of the Valk intake system to answer that either. Seems to me a vacuum leak can do that but I am not sure. Would it throw off the pulse count or just make the vacuum pulses weaker in inches of mercury.

[indybobm]

So it only monitors one channel and ignores the rest, no matter which one is connected.

[Zer]

I had the same issue with the bike tach reading differently from the Digisync.  I put an old wired tach on to double check and it matched the digisync - not the tach on the bike.

[The emperor has no clothes]

I suspect the bikes tach is not as accurate because it is taking electrical impulses and converting them into a mechanical dial. The DigiSync takes the vacuum pulses and displays them digitally. As an aside Harry, when you get done with your DigiSync I recommend removing the 9 volt battery and putting it separate in case of leakage.

[WintrSol]

So it only monitors one channel and ignores the rest, no matter which one is connected.

I don't know if it picks the channel with the best signal, or goes down the channels, in order, until it finds pulses to count; which method could affect the results. I do know that, if the pulses are marginal in strength, it will give poor results. I added some 'shade tree' vacuum ports to my old CB450, and got some fairly random readings in both rpm and vacuum; back to the dial gauges for that bike.

What I'm saying is, if it goes down the channels in order, and the one it picks first has vacuum issues, like one that is shared with the petcock, it could be less than accurate. Hooked up directly to the ports, with no kinks in the lines, it perfectly matches my hand-held digital tach.

[Harryc]

I had the same issue with the bike tach reading differently from the Digisync.  I put an old wired tach on to double check and it matched the digisync - not the tach on the bike.

How did you hook up the 'old wired tach'?

[Pete]

Thanks Bill. So I took a look around and what I have on hand is an old Sears Engine Analyzer with a tachometer. It has (3) connections, (2) for the battery and (1) for a coil connection. It has 4, 6, and 8 cylinder settings. Is this something I could use on the Valk and if so where do I hook the coil input to get a signal?

The coil pickup is monitoring sparks from a single coil. That is why it needs to know cylinders.
Keep in mind that a 8 cylinder actually fires only 4 plugs per revolution, 3 for a 6 cylinder and 2 for a 4 cylinder. Auto ignitions generally do not fire every plug ever revolution, only every plug in 2 revolutions.

The Valkyrie is different it is a 6 cylinder, but from a coil perspective it is really 3 2 cylinders engines (3 coils each firing 2 cylinders) and the coil fires every revolution.

So in two revolutions a Valkyrie fires 2 times thru a coil. (Ignore the fact that it fires 2 plugs at the same time, it is just 1 firing).

So you need a setting for 2 cylinder, which you do not have.

But if you set the tach to 4 cylinder the tack may read 1/2 actual as it will read 4 firings for 4 revolutions rather that 4 firings in 2 revolutions.

[Harryc]

Thanks Bill. So I took a look around and what I have on hand is an old Sears Engine Analyzer with a tachometer. It has (3) connections, (2) for the battery and (1) for a coil connection. It has 4, 6, and 8 cylinder settings. Is this something I could use on the Valk and if so where do I hook the coil input to get a signal?

The coil pickup is monitoring sparks from a single coil. That is why it needs to know cylinders.
Keep in mind that a 8 cylinder actually fires only 4 plugs per revolution, 3 for a 6 cylinder and 2 for a 4 cylinder. Auto ignitions generally do not fire every plug ever revolution, only every plug in 2 revolutions.

The Valkyrie is different it is a 6 cylinder, but from a coil perspective it is really 3 2 cylinders engines (3 coils each firing 2 cylinders) and the coil fires every revolution.

So in two revolutions a Valkyrie fires 2 times thru a coil. (Ignore the fact that it fires 2 plugs at the same time, it is just 1 firing).

So you need a setting for 2 cylinder, which you do not have.

But if you set the tach to 4 cylinder the tack may read 1/2 actual as it will read 4 firings for 4 revolutions rather that 4 firings in 2 revolutions.

Thanks Pete, I am following what you said. So to hook up my single coil input old style tach, would I just pick one of the coil packs and hook to one of the yellow/other color wires or should I remove the headlight and hook to the bikes tach signal wire? I am guessing coil input wire from the ICM (at a coil pack) which is yellow and another color depending on the coil pack. Multiplying the reading x2 would not be a problem for this test...this tach has fairly fine increments.

[Zer]

I had the same issue with the bike tach reading differently from the Digisync.  I put an old wired tach on to double check and it matched the digisync - not the tach on the bike.

How did you hook up the 'old wired tach'? Smiley


My tach tied into the battery and then had the clip that attaches around the spark plug wire.

[Harryc]

I had the same issue with the bike tach reading differently from the Digisync.  I put an old wired tach on to double check and it matched the digisync - not the tach on the bike.

How did you hook up the 'old wired tach'? Smiley


My tach tied into the battery and then had the clip that attaches around the spark plug wire.

Thanks. So I am the third person who can confirm the bikes tach is inaccurate. I hooked the old tach to a coil input wire and set it up like Pete said. He was absolutely correct. Set it on the 4 cyl setting it halved the rpm and matched the Digi Sync perfectly. So the final verdict in my case is the Digi Sync is accurate and the bikes tach is off by 200rpm (again by eye). I'm leaving idle speed set by the Digi Sync and my old Tach. I did try different intake ports with the Digi Sync by the way, no difference so Bon S was right too.

[Harryc]

Harry, when you get done with your DigiSync I recommend removing the 9 volt battery and putting it separate in case of leakage.

Will do, thanks again!

[Leathel]

What are the Digi Sync's worth and where do you get them.... When I am done with the carbs I will have a need for one

[98valk]

is this the std/tourer tach or I/S tach?  I tend to remember I/S tach was know to be off compared to std/t as posted by various owners.
My digiS showed exactly same as my std tach.

[Harryc]

is this the std/tourer tach or I/S tach?  I tend to remember I/S tach was know to be off compared to std/t as posted my various owners.
My digiS showed exactly same as my std tach.

I have a Tourer, not sure what the others have.

[Harryc]

What are the Digi Sync's worth and where do you get them.... When I am done with the carbs I will have a need for one

Hey Leathel, here's the link - http://www.thedigisync.com/

[Leathel]

What are the Digi Sync's worth and where do you get them.... When I am done with the carbs I will have a need for one

Hey Leathel, here's the link - http://www.thedigisync.com/

cheers, will look in to it

[sdv003]

is this the std/tourer tach or I/S tach?

Mine is a 98 Tourer

[Harryc]

is this the std/tourer tach or I/S tach?

Mine is a 98 Tourer

Answered the same question above, but mine is a '97 Tourer. I am not sure what bikes the other (2) folks who reported inaccurate stock Tachs ride.