750 twin and Mallory Hyfire - moved from 'Coil recommendation for '79 750 twin'

Seems I'm a bit of an idiot. I posed a simple (to me, anyway) question to the Mallory tech support folks:

I am planning to install a hyfire VI-aL on a 78 KZ750 twin. Is there a way to use the rev limiter on a 2 cylinder engine, or should I set it for no limit?

Their response:

That box will not work on a 2-cyl engine.

I was a bit more curious, so I thought another question was in order:

Do you mean it will not work, or will not provide a rev limit? The engine configuration is one which provides a spark for every revolution.
There is one coil which provides a spark to both spark plugs at the same time. I believe that it is referred to as a 'wasted spark' ignition. If that is the case, using a magnetic pulser to trigger the Hyfire module once per revolution, I should always get a spark when needed, using the current mechanical advance for timing?

Their response:

It will not work on a 2-cylinder engine ... 4-6-8 only!

Still not satisfied, I asked:

Could you please explain why that is? What exactly makes it specifically for 4, 6, or 8 cylinders, besides a couple of switches on the circuit board?
What circuitry is affected by the switches, besides the logic for the rev limiter?

Their response:

I can't make it any clearer ...

Those units ONLY support 4, 6, or 8 cylinder engines. They do not accept or recognize a 2-cyl firing cycle, and will not batch fire like the system you have.

These ignition units are NOT compatible with a 2-cylinder engine. It is specific, black and white, and won't work! The Part #685 box will work with 3-12 cylinder engines, but again NOT 2-CYLINDER! Even then, you have to tell the box how many cylinders you are using through programming on top of the unit. These units were never designed to work with 2-cylinder engines and are therefore incompatible. Telling you specifically "again" IT WILL NOT WORK ... You cannot adapt it to work, rewire it, wave a magic wand over it, pray over it ... NOTHING will make it compatible with a 2-cylinder engine.

I never mentioned anything with the Rev Limiter feature ... I'm saying that none of the Mallory Hyfire units will work on a 2-cylinder engine, not even considering a rev limiter. I've now said this THREE times.
How many ways do I need to tell you that it won't work without being rude?

In fact, I'm having difficulty in understanding why someone (based upon your job) wants one of these on a motorcycle, where you plan on mounting it (it is not small), and why you cannot take NO for an answer.
Maybe you are not using the engine in a motorcycle, but even then ... It won't work with a 2-cyl, and is completely incompatible with the system you have.

Best Regards,

Sales Support
Century Performance Center, Inc.
www.centuryperformance.com
ph (775) 746-4887
fax (702) 953-0705



Wow, I really didn't think I was that unreasonable, maybe I need to go take a nap or something. This is really making me want to get this installed and working correctly. I think I should even get the rev limiter working, and verify that I can get a correct tach signal out of it for use in my Megasquirt. It all worked very well on my v8 Jeep motor. Then I will have to send their tech folks a little video of it running, along with a little narrative concerning their helpful nature!!!

Sorry for the rant, but these guys really got to me today...

I just noticed the replies came from Sales Support, maybe I should have them direct my questions to some real technical support folks?

Post edited by: securitygeek, at: 2006/08/17 16:17

In fact, I'm having difficulty in understanding why someone (based upon your job) wants one of these on a motorcycle, where you plan on mounting it (it is not small), and why you cannot take NO for an answer.

Interpretation, "I know everything and you are stupid, so just do what I say and shut up!"

I have met to many people like that

This thing is for use with a distributor, right? In that case it triggers the coil once for every triggering event, and the 750 twin uses one coil, so what's the problem?

Course it's going to be nothing more than a glorified oversized ignitor, but it should still work, at least it should if you have an appropiate trigger (as in points, appropiate pickup coil, etc).

I bet Lou could have it wired and running in no time (and I'm serious)

Well, that tears it. We have to get it to work on a 2 cylinder engine. Period.

Let me know when you're ready to get started.

The thing is, you asked "why?". He didn't answer that. I run into these guys all the time.

if i might jump in....
dude was rude no matter how u slice it....

and i think that the 4-6-8 switches change the dwell settings...i am not positive though

But....that box will run a twin with a waste spark setup.

i use GM cdi coils...and resistor wires. the ones on my bike are from a 94 cadillac deville with a northstar v8 and have a 1.7 ohm resistance..but most of the gm cars in the early 90's used these...grand ams,luminas, especially the front wheel drive v6 models. they have twin towers. and make a whopper of a spark.

i have these paired with a gerex cdi box...which works pretty much the same as your box but is a dual channel..yours should be a single channel.
i see no reason why you couldnt power your twin with your box...
ive run chevy HEI modules on cb350's....bet gm will tell you that wont work either..but it does. i am currently building the ign for a kz900 for my brother..it will use a coil pack from a dodge neon and a gerex setup simular to mine.
i can take some picks of my homemade coil pack setup if you would like it.

Ed

I really dislike these sort of people. Steell, I figured the same as you. Get a trigger event, either from the original points or from the magnetic pickup from the 440 electronic parts, and it causes the coil to spark. Pretty simple to me!

Of course I had to ask about a non-standard use, and the question went to a sales support person, not a techy type person. I guess I stumped him, and just made him mad enough to embarrass him or something like that.

I was just looking at it, and know it is as simple as hooking it up the same as their own points use diagram in their own manual. That does not answer my question about the possibility of using the rev limiter. I will just have to experiment on that one. Too bad it is so late, I can't run the bike at this hour I did hook it up, and tested the sparking action. Very big, fat, hot spark. It just has to be at least 20 times better than the stock setup. The guy from Mallory is right though, it is pretty large for a motorcycle. That doesn't mean that I wont use it. Especially when he says it WILL NOT WORK!!!

With a response like this: "Telling you specifically "again" IT WILL NOT WORK ... You cannot adapt it to work, rewire it, wave a magic wand over it, pray over it ... NOTHING will make it compatible with a 2-cylinder engine." I think I will tell him that all attempts to adapt it, rewire it and the waving of my VERY BEST magic wand failed. It simple WOULD NOT WORK, as he said, until I finally did PRAY OVER IT, and that was the only thing that did it!

It will work just fine, of that I am sure. Thanks for listening guys, I'm now off to bed. Good night all.

On the rev limiter, simply set it as a four cylinder and set the rev limiter at 1/2 the desired rpm limit.

Guess I probably ought to explain

That box is normally triggered from a distributor on a car engine. A distributor on a car engine turns at 1/2 crank speed, so on a car four cylinder the distributor will generate four spark events per distributor revolution, thus two spark events per crank revolution. The 750 twin is triggered off the crank, and generates one spark event per crank revolution, vs two on a four cylinder car. so the box will see one half of the spark events per crank revoltion on the 750 twin that it would on the four cylinder car motor. Set the rev limiter at 4k rpm and the actual limit will be at 8k rpm on the twin.

Clear as mud?

Well Steell, that is actually about as clear as the lakes around here, better than mud, but not Evian! Really, that is along the same lines that I was thinking, I don't really know why I thought the product tech support guys would be able to confirm that for me though. I should have them put your email address on their web site for contacting tech support. Hopefully I will be able to actually work on it this evening, or at least this weekend.

What kind of adjustment controls are on the thing? Maybe you can point us to an online manual just so we can all be on the same page. Steel is right about the rev counting. The Twin will give the box half the signals of a 4-cyl car.

Dwell is not an issue with CDI. However, I would expect that there is an RPM at which the multi-sparks reduce to single spark, which is common on MSD. This will happen at an RPM twice as high as on the car. So you will still be getting multi-spark at higher RPMs than was intended. This may not be an issue at all, but I wonder if multi-spark at higher RPM can cause knock. I guess wait and see.

Here is a link to the manual. The only adjustments are the switches to make it work on a 4-6-8 cylinder (notice that IT WILL NOT WORK on a 2 cylinder motor - no way no how) and a rotary switch along with a couple more switches to set the rpm limit. I think the multiple spark cuts out at 3k normally. So you think that would really be 6k on a twin? If that is the case, I might want to set it up for running as if it were on a v8, so the dwell would be a shorter duration, to lessen the chance of potential problems ar higher rpm?

EddieBoy wrote:

i can take some picks of my homemade coil pack setup if you would like it.

Of course we would like pictures, we always like pictures of what others have set up, painted, machined and other stuff...pictures are coooool

There really isn't a question of dwell in a CDI system. The capacitor is charged by a high-frequency pulse to create a high-voltage. The high-voltage is then slammed into the ignition coil when the trigger signal is received. Multi-spark continuing too long may not be a problem.

The trigger signal is different on the KZ from a typical car trigger. The KZ has a long ramp before and after the AC spike.
The details are on the link marked gpzreluctor.gif on my HEI page.

www.geocities.com/loudgpz/GPZgmHEImod.html

It may not be an issue since CDI is looking for a single trigger event (as opposed to some electronic ignitions where dwell IS the issue).

Just thinking out loud here, too, I guess.

ok....ive been thinking and thinking..
on a 750 twin,...are both pistons at tdc at the same time?....and not opposed? meaning cyl 1 is at tdc and cyl 2 is at bdc.
im pretty sure with out ever looking into a 750 twin...that they would both be at tdc at the same time..

when cyl 1 is on the firing stroke then cyl two must either be at the beginning of the intake stroke or a firing stroke.
i assume that cyl 2 would be on the intake stroke...

when cyl 1 fires then cyl 2 draws in fuel..cyl 1 then comes to exhaust...cyl 2 compresses...so on...

do the 750 twins have one or two pick ups?or point sets?
i will assume that it has one trigger event per crank shaft rotation. then it would have two spark events per four cycles.
that means if you triggered cyl 1 at tdc on the firing stroke then you would also be firing cyl two at the very end of the exhaust stroke...cyl 1 moves to bdc and cyl two draws fuel as it also moves to bdc..thats one stroke or one half turn of the crankshaft.
now cyl 1 moves to tdc again this time pushing the exhaust out..as cyl 2 compresses...this is stroke 2 and also one half crank rotation.
now cyl 2 fires and moves to bdc and cyl 1 draws fuel...stroke 3
cyl 1 now moves to tdc and compresses then cyl 2 also moves to tdc and exhaust is pushed out.

ok so..lets say at 100 rpm of crank rotation the box actually thinks the crank is spinning at 200rpm.
then at 6000rpm the box would think the crank was spinning at 12000 rpm.
i think the only way to use the rev limiter would be to either use a 24000rpm limit to get a 12000rpm limit.
or put a magnetic pickup on the cam shaft..but then you would need two pickups to retain the two spark events.
if you didnt have two then cyl 1 would fire and go through four strokes but cyl 2 would be dragged for four strokes..
unless.....cyl 1 and cyl 2 both fire,exhaust,compress and intake at the same time...then its essentially a single cyl with two pistons.
if that were the case then and you had two trigger events per crank rotation then it would fire once on the firing stroke and once again on the end of the exhaust-begining of intake stroke. spark would be wasted on both cyls at the same time..instead of one firing and one wasted.
either way the box sees two spark events per four strokes..instead of one. if the trigger is on the crank shaft.

so....does this sound about right so far?