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Discussion Starter · #1 ·
Well the good folks of this forum just informed me about a sweet mosfet r/r mod that I will definitely be upgrading in the near future.
http://roadstercycle.com/Shindengen FH012AA Regulator upgrade kit.htm

This raised another question in my mind that seemed appropriate to start in a new thread. What are the options for upgrading an ignition system on an 83 vt750? The timing and synchronization of a mod seem they would be troublesome to get correct. The ignition coils seem pretty straight forward to mod, but the pulse generator and spark units I'm not sure about, mostly because I'm not sure what those units are doing. My basic understanding (or misunderstanding) is that the pulse generator is controlling the ignition timing and must be in sync with the camshaft or something. It sends a timing pulse to the spark units telling them to send a blast of current to the ignition coils. I assume the spark units are some barbaric transistor style switching which I would like to upgrade to mosfets. So then the spark units send their pulse of current to the ignition coils and the coils do a turns ratio voltage conversion up to the 25-35kV needed for the spark plugs. But that's just my guess. Any knowledge on the subject will be greatly appreciated.
 

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About the only thing you can do on the ignitin is better coils and wires and the "Timing Advance" mod. The pulse generators are just magnetic prox sensors, telling CDI box where piston is. CDI box controls timing and fires the coils, spark voltage is generated by the coils, coils fire the plugs.
 

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Discussion Starter · #3 ·
What does CDI stand for? Is this the same as what the honda manual refers to as the spark unit (even though it's not really sparking anything). No one sells CDI boxes with variable timing adjustments? I'll do a little more research but you'd think instead of manually moving your magnetic sensors for the timing advance mod you could instead buy a nice CDI and tweak the timing electronically with a potentiometer or something. Obviously you'd still be triggering off the magnetic sensors but the timing delays you could dial in yourself. Well it just seems like one of those things that someone else would have made by now.
 

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The box on the Bike is automatic RPM advance, it controls the timing. It is variable, just not adjustable. That box will work if you only plan to run at a fixed RPM, like a lawn mower. There used to be aftermaket boxes, like from Power Commander and others, but they've been off the market for years.
 

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Fuggetaboutit - just be glad if you get the bike back to very good running stock condition. The minimal amount of increase for aftermarket - high energy - ignition/coils, wires and varilable ignition timing (if they even exist for your model/yr) is not going to buy you much in hp increases. You are essetntially trying to hot-rod a tractor motor........
 

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+1 on that.

People have gone all out on these Shadow engines. Custom exhaust, fuel injection, turbos even. Then add high energy ignition, MSD, taller cams, domed pistons, etc, etc. The most I've ever seen posted at the dyno is a 20% increase in power, and even then only in specific RPM ranges.

Big deal.

If you want performance, get a performance bike. If you want to love the ride and get home reliably, enjoy your stock Shadow.

FYI, CDI stands for Capacitor Discharge Ignition. It's what replace TCI (transistor-coupled ignition) back in the early 1980s.

--Justin
 

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Discussion Starter · #8 ·
Well I'm not trying to get any extra power; by "mod" I mean a cheap alternative to the stock part so maybe I should call it a "hack" to not give the wrong impression. I just know I have an old bike with old parts and they're going to die at some point so I'm diggin around trying to see what my options are. A CDI seems simple enough that I figured there might be some mods that are cheaper than the stock part. So back to the technical part of the discussion, is it actually the CDI doing the RPM advance or is that do to the trigger head design? Or it depends on the bike?
 

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Ah!

The CDI unit does all the calculating for spark advance on its own. The pulse generators in the engine are fixed at "full" advance, and the spark unit adds the appropriate delay at lower RPMs.

As for a replacement, I highly recommend IgniTech of of the Czech Republic. They build fully programmable CDI replacement units at a very, very reasonable price. You tell them the make, year and model of your bike, and they'll build you one with the right harness. For a bit more money, you can get one with a computer interface, so you can program your own advance curves into it. Very neat!

Their customer service is good too!

IgniTech

--Justin
 

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Discussion Starter · #10 ·
So you've had them make you a CDI? And was it cheaper than buying the stock part? That sounds like a good option to me. So does the CDI use the time between the previous trigger and current trigger as a reference to the rpms and then delays the pulse output proportionally to that time difference? I know I'm getting a bit over-technical but I'm curious how this thing actually works.
 

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So you've had them make you a CDI? And was it cheaper than buying the stock part? That sounds like a good option to me. So does the CDI use the time between the previous trigger and current trigger as a reference to the rpms and then delays the pulse output proportionally to that time difference? I know I'm getting a bit over-technical but I'm curious how this thing actually works.

Yes, they built a custom CDI for my buddy's 1982 Virago. it was top-notch and cost about $200.

The system has three linked circuits in it. One counts the pulses coming from the pulse generator in the engine and uses some simple math and a timer to determine the RPM. This data is fed to the second circuit that calculates the spark advance required for your particular engine. In the high-end version of the unit, this circuit is programmable, so you can build custom advance curves. This data is fed to the third circuit which creates the required delay between the arrival of the pulse and the firing of the ignition coil so that the spark is properly timed for the RPMs of the engine at that exact moment. Works slicker than anything!

--Justin
 

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Relay added to put power directly from the battery to the coils. Freed up about half a volt losses through the motorcycles original system.
 

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Discussion Starter · #14 ·
Relay added to put power directly from the battery to the coils. Freed up about half a volt losses through the motorcycles original system.
I'm know close to 0 about ignition systems. A relay where? Instead of the charging capacitor? Wouldn't that sink a sh*t-load of current off the battery? Oh, you mean instead of charging a cap and then discharging on trigger you flip the relay on trigger? A power mosfet relay? More details would be much appreciated.
 

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Discussion Starter · #15 ·
It was top-notch and cost about $200. The system has three linked circuits in it.
That doesn't sound any cheaper than the stock part BUT for the money it does sound much more intelligent. Will they make a less intelligent CDI for cheaper? Precision calculation of rpms and timing advance is nice and all but like I said earlier, I don't really care about a little extra power, I just want a cheap (yet efficient) alternative to the stock part.
 

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I'm know close to 0 about ignition systems. A relay where? Instead of the charging capacitor? Wouldn't that sink a sh*t-load of current off the battery? Oh, you mean instead of charging a cap and then discharging on trigger you flip the relay on trigger? A power mosfet relay? More details would be much appreciated.


Leave the trigger system alone. There is battery power supplied to your coils at all times the ignition switch and kill switch are on.

The wires in the bikes harness are quite small AWG as well. By adding a relay and power directly to the coils from the battery through the relay you bypass the crappy wiring, and the two switches that it needs to get through before getting to your coils.

The trigger for your new relay uses the original power wire. That way your ignition and kill switch still work.

I freed up about half a volt to my coils with this. Well worth it IMO.




 

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Discussion Starter · #17 ·
Well I'm a little confused as the what the CDI is doing then. I thought as the CDI capacitor charged, it slowly allowed current through the ignition primary coil and on the trigger pulse the cap/coil circuit gets shunted to ground allowing the current to quickly discharge providing the high voltage on the ignition secondary coil. If there is always current running through the primary coil supplied by the battery, how is the CDI able to create the quick discharge?
 

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Your understanding of ignition systems is correct for magneto and standard inductive ignition. CDI is a bit more complicated. This article should help you understand how it works, and also why your Honda makes a pale yellow spark and not a fat, blue "Briggs and Stratton" spark:

Capacitor discharge ignition - Wikipedia, the free encyclopedia

--Justin
 

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Discussion Starter · #19 ·
Unless I'm missing something, Wiki makes it sound like the CDI charges a capacitor and then discharges the current through the coil thereby creating the high voltage. For an inductive discharge ignition it sounds like you run current through the coil and then disconnected to collapse the magnetic field thereby creating the high voltage. So when "still bluenoser" talks about sending battery current straight to the coil via his relay, it sounds to me like IDI not CDI. So I'm obviously still missing some subtle details about this.
 

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Right.

Bluenoser isn't saying anything at all about a relay actually controlling ignition timing. Not one bit.

What he's saying is that the power that goes to your ignition modules has to go from the battery, through the ignition switch, then back to the ignition modules. Age and corrosion reduce the voltage that gets to the CDI units on our older bikes. What he's saying is that if you connect a relay's contacts directly from the battery to the CDI unit, then control the relay by powering its coil from the power coming from the ignition switch, you get direct battery power to the CDI units. His results show getting up to 0.5 volts more at the CDI unit, which is a lot considering the step-up ratio of the CDI and coils. 0.5V into the CDI can result in 1,000 more volts at the spark plugs.

--Justin
 
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