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How A CDI Works (Gen 1)

38K views 33 replies 6 participants last post by  Damocles 
#1 · (Edited by Moderator)
"What you always wanted to know about your CDI, but were afraid to ask!"

I share this YouTube video clip with you, fellow Generation 1 fans, because . . . it is VALID!!!!!!!!!!

In my limited research, I found several YouTube video clips PURPORTING to explain CDIs; however, I found them quite erroneous/incomplete/misleading/etc.

This one, though simplified, you can generally take to the bank, operational principle-wise:



CAVEAT: Remember, I said, "Generation 1." Generation 2s have no CDI (Capacitive Discharge Ignition) whatsoever.

Enjoy the show! :)
 
#2 ·
Awesome thank you. This is also the basic principles for kick start magneto driven bike, boat outboards and airplanes.......nice add....sticky please!
 
#4 ·
Here's some verbiage extracted from a comment I made on the Generation 2 thread:
I mentioned the Generation 1 presentation was simplified; refinements I'd expect in the real-world as-built condition: First, the AC coming from the exciter coils could easily be stepped-up with a transformer; I expect the elves who assembled Generation 1 KLR650s performed that very trick--say, going from maybe 100 VAC to 400 VAC. Next, the schematic shows a half-wave rectifier (the diode, D1?); no reason not to put in a full-wave rectifier, increasing the capacitor-charging coulombs-per-revolution by about 100 % (i.e., nearly twice that of a half-wave rectifier). So, by these refinements, the voltage is increased by a factor of 4, and the charging time and thus, current, by 2.
Disclaimer: Don't know that these refinements actually exist in the Generation 1 CDI; speculation only.
 
#5 · (Edited)
Finally looked at the thread. Has anyone de-potted...un-potted...reverse-potted a Gen1 CDI?

I'd expect it has a more sophisticated circuit than the one illustrated, including advances such as mentioned. It will almost certainly have some means of compensating for temperature effects on switching, etc.

Has anyone run the KLR CDI on a test bench or 'scoped to see whether the ignition advance is processor based within the CDI box or due to stepped trigger coil core?

It's been on my list of things to do but don't seem to get there.

Here's a "make your own" CDI for small engine which explains some mpre advanced features often found in commercial CDI. The stepped core for trigger coil explanation is what I referenced higher up. Interesting and "simple" concept. It would seem that an advance "curve" rather than linear advance could be possible with such a design.

http://archive.siliconchip.com.au/cms/A_110499/article.html

This also illustrates the hard to convey concept of the effects of trigger coil air gap on timing and timing advance.
 
#10 ·
http://archive.siliconchip.com.au/cms/A_110499/article.html

This also illustrates the hard to convey concept of the effects of trigger coil air gap on timing and timing advance.
Thanks for the link, Normk; however . . . I missed the trigger coil air gap effect discussion in my first reading; gotta go back and read it again! :)

For programming the ignition map, looks like we need to take a look at this article:
To replace one of these units, you could adapt one of our previous designs, such as the High Energy Ignition (SILICON CHIP December 1995 and January 2006) or the Multi-Spark CDI (September 1997). Alternatively, you could consider using the Programmable Ignition System from March, April & May 2007.
The spark advance of the CDI on Kawasaki V-Twin ATVs (Prairie, Brute Force, etc.) is determined totally by engine rpm input (trigger coil impulse rate), electronically, without manifold vacuum input.

Aftermarket, wire-on modules ADVANCE the initial spark timing and allow the engine to stand the quads up on their hind legs (the factory configuration retarded the spark to prevent end-overs by enthusiastic but unfamiliar/unskilled riders, hoping to reduce vulnerability to product liability claims).

So . . . no reason NOT to incorporate manifold vacuum as an ignition timing input parameter (along with rpm and perhaps throttle position, etc.), but . . . not typically done with motorcycle/ATV CDIs today, AFAIK. Spark timing is varied electronically with input only from trigger coil pulse frequency, seems to me.

Gotta find that, "Programmable Ignition System" article from March, April & May 2007! :)
 
#6 ·
Here's a "make your own" CDI for small engine which explains some mpre advanced features often found in commercial CDI.
WHERE, Normk? :)

Saw no image nor link in your post.

Good point. KLR650 hop-up aficionados have fooled with trick valve timing, etc., allegedly gaining horsepower, but . . . WHO HAS EVER TRIED OPTIMIZING THE IGNITION ADVANCE CURVE MAP?????????????

WHO HAS EVER EVEN ADVANCED SPARK TIMING? (May need high-octane fuel, but . . . there could be some extra power there.)

(I'm not even going to bring up INCREASING COMPRESSION RATIO!!!!! :) )
 
#7 ·
Strange.....you usually complain when I include links. ;-)

Someone was posting regarding changes to advance curve and one could likely achieve some success through monitoring intake vacuum at a given throttle opening. Problem is, the KLR carb has no easy means to attach a TPS (throttle position sensor) and single cylinder engines are a real tough call for MAP sensors.

When determining ignition advance curve from scratch, the only way I know to do so is to monitor for detonation while experimenting/monitoring ignition timing at wide open throttle. Once one as determined maximum advance during the progression from minimum to maximum RPM at wide open throttle and assumed maximum temperature, one has a basis for timing the engine. This is generally where bikes stop.

Assuming the same cylinder filling, combustion rate/burning rate requires a certain amount of time. Let's call it "X" miliseconds. If the spark ignites the air-fuel mixture at a piston position which allows "X" milliseconds of burning time before the piston reaches the top, then double the RPM and the piston will reach top before the burning is completed if the spark occurs at "X" milliseconds, correct?

For this reason, the spark must occur at "X" milliseconds and not at a specific piston position, correct? So, since the spark is timed from crankshaft (or camshaft = same effect) position, it must be fired earlier in terms of crankshaft (piston) position as RPM increases in order to allow "X" milliseconds for burning. So, we must advance the timing (spark firing point) as RPM increases. Note that I have taken license in the explanation but the trend is correct. Note also that the amount needed to time correctly is no linear.

Since combustion rate/burning rate is at maximum at WOT and high temperature, one can assume that the burning rate will be slower during smaller throttle openings because smaller throttle openings provide less compression pressure and so slower burning rate. For this reason, partial throttle requires earlier spark firing in order to provide for the "X" milliseconds + added time.

In order to do this, one requires either a reference of engine load, usually by intake manifold vacuum or air flow rate compared to engine characteristics.

If one inspects a conventional automotive distributor, one will find centrifugal weights which provide speed related advance and a vacuum chamber which provides for greater advance as engine load is decreased.

How to do this for a KLR? Well, as above generally but in the final analysis it's far more difficult. Far easier to combine with fuel injection and therefore use the same air flow and engine speed data combined with experimentally supplied look-up pages.

I've worked with this problem on multi-cylinder engines which is doable. As for a single like the KLR with huge intake pressure pulses....there lies madness. :)
 
#8 ·
The CVK40 used on the Vulcans had a TPS. All we need is a cheap and ready source of CVK40 pumper carbs...

The FI solution seems to me to be the most effective, as Norm states. There has been some success with a MicroSquirt unit.

The problem with those threads is that they usually go up to the point of final installation and tuning and then the poster disappears. Long term data is lacking, and the MPG and dyno results I read about were quite disappointing (though all of that may have been on the tuner).

Tom
 
#9 ·
It might be instructive to understand that a typical V8 from days past would add about 15 degrees of advance during cruise over what there would be at the same RPM and wide open throttle. On the road, one could play around to find whether the engine might tolerate more advance at some (or all) engine speeds and wide open throttle.

Clearly, there would be some fuel mileage advantage to be gained by providing a "vacuum advance" but doing so is another bucket of worms.

This might be "fun" in the same was as is having a prostate exam due to the KLR's trigger coil location and that one would require some means to modify the RPM to advance relationship. This is really easy in the minds of those of us who lack the electronics capacity to design such a circuit but doable. Problem is that it doesn't simply require an increased advance uniformly applied through the RPM range. There are units (or were) on the market which would allow a uniform advance of the entire advance curve. Problem with that, is that, one will experience one point at which advance is too great while others would benefit from more advance.

For this reason, a processor is required which will consult pages of data to compare engine speed and to output the desired advance. Such a system might incorporate intake and engine coolant temperatures to further refine because hotter conditions speed combustion and so tolerate less advance.

Then the engine load question which is added to the look up pages for modern fuel and ignition systems.

In the old days, we would add a detonation sensor and processor such as the one made by MSW. This worked well because we'd shove the timing up to the point where one would experience detonation ...just... then some more. The detonation sensor would detect combustion explosions then retard ignition timing. This worked quite well for many V8's because the detonation sensor and processor had enough sensitivity and range.

One can still test detonation sensors by idling the engine, and using a 10 mm combination wrench to tap the sensor or close by which will cause the sensor to output and the timing to be retarded. Think of the chances that an engine as rattly as the KLR's will be the ideal partner for a detonation sensor...

I've also avidly followed a number of EFI or other processor projects which have disappeared. My conclusion has been that things weren't working out and were finally dropped. Not many will come back onto a thread after a big build-up to admit failure. Especially as there will be so many people who have never touched any of this stuff who will know exactly what should have been done. :)

I'm still interested to hear whether anyone has determined whether and how much advance is built into the CDI unit or whether some or all the advance is due to a stepped triggering.
 
#11 ·
This is an excellent discussion! The Damocles video should be a must watch.

Been pondering the same issues. Was hoping some poor KLR rider's CDI mounting bolts would vibrate off and I'd find a CDI in the street to de-pot.:fiddler:

Interesting thought on how much effort goes into cam timing and carb tuning and zero into advance curves.

The AU article and the stepped core idea is nifty. I was thinking we had a magnet in the coil and a reluctor lump on the rotor (?) so might work better or worse?

If the CDI / pickup coil has an advance curve, could you measure the advance with an old fashioned inductive pickup timing light?

I have a $70 single channel scope. And am building an Aduino datalogger. Still trying to figure out if I can get an advance curve using all of the above.

Re: TPS -- I've heard that the Gen 2 bikes have a potentiometer in the throttle control assembly-pretty cheap on ebay
. If somone can confirm that's true, I'll buy one and include it in my project

Also thought about a slide position sensor. I'm thinking (without trying it) that the slide position could be mapped to a vacuum signal taken from the carb top cover. Vacuum force & spring rate determine position exactly (I think) unless,the slide gets hung up (stiction)

On the manifold vacuum measurement- my old fashioned Bourdon tube gauge is bouncy, but you can still estimate it. I think a digital filter with a long time constant (10-20 revolutions) would be fast enough to do meaningful Arduino control of spark advance. All the arduino would need to do is send a 5v signal to replace the pickup coil signal(? Hypothesis)

So many thoughts, so little time. Any comments or help on my projects would be much appreciated
 
#12 · (Edited)
If the CDI / pickup coil has an advance curve, could you measure the advance with an old fashioned inductive pickup timing light?
Yes!

I think a procedure exists in Clymer, or perhaps in the factory Service Manual, where a timing light is used to verify spark advance vs. rpm.

As I understand the OEM arrangement, the pickup coil and timing mass on the rotor send a trigger pulse to the CDI at the same angular flywheel rotation angular position, regardless of rpm. The spark advance is determined electronically, depending upon the frequency of trigger pulses.

CAVEAT: Postulation, speculation, and wild guess on my part: No authoritative reference available. Only . . . since the geometry is unchanged between the timing mass and pickup coil, and the only trigger input comes from the pickup coil connection, the theory/premise seems plausible, to me; although it may be totally in error.

========================

That said, don't know how the Generation 2 spark advance might be structured; perhaps similarly: Pickup coil pulse rate electronically determines advance of ignition coil electronic switch opening (consequently inducing a spark from decay of electromagnetic field in ignition coil primary winding, "stepping up" voltage via the secondary coil winding).

--------------------------------------------

Interestingly (to me, anyway), the Generation 1 and the Generation 2 ignitions perform in decidedly opposite ways: An electronic switch CLOSES a circuit in a Generation 1 ignition, discharging a capacitor across the ignition coil primary windings, "transforming" a high voltage in the secondary winding to produce a spark; while an electronic switch in a Generation 2 OPENS a circuit (the saturated primary ignition coil winding) to induce a high voltage in the secondary windings producing a spark . . .

======================

Oh, yes; must clarify! The CDI video is not "mine," it was only discovered by me on the Internet! I thought the URL would sufficiently indicate its source, but the URL does not show (unless you "quote" the post where it's contained), since the video clip is embedded. Wish I could claim credit, but . . . I'd have to violate my anti-plagiarism principles to do so! :)
 
#13 ·
CDI (which discharges a capacitor to obtain high magnetic flux increase) is common place in small engines while automotive tend to use magnetic field collapse because of the higher electrical capacity of automotive systems. Magnetic field collapse is the system used with breaker point ignitions powered from the battery. It is generally a bit simpler to avoid the use of the extra stator winding needed to create the charge current for the capacitor by using the DC power from the battery system.

I'm surprised that Kawasaki hadn't done this from the outset but lots of these things hold over. It would be simple enough to convert a Gen1 to use a Gen2 module, assuming trigger coil compatibility, but converting Gen2 to Gen1 module would require a stator change. This is fairly common in dealing with older engines such as the EM600 Honda in the garage at the moment. Belongs to a family member and CDI box is bad and not available. I'm waiting for a small motorcycle module to arrive to get that one going.

I jumpered a GM HEI distributor module with small battery and 12 volt motorcycle coil to check the engine's other condition by running it before ordering. The 'scope showed reasonable trigger and charge coil patterns. One could convert in the manner I jumpered but this would require a battery which would complicate, add expense so converting from "Gen1 to Gen2" seems a poor option. I'm going to try a motorcycle CDI as that will likely charge and trigger.

He has an acquaintence who offered the use of a running EM600 so will check the ignition advance once we determine a means of placing marks on flywheel or fan. I don't know if the EM600 has fixed ignition timing as typical of most older small engines, or whether it has a module based advance. If it runs a fixed advance, and the motorcycle module adds advance, this could be a problem.

Other issues are that there are various trigger strategies used, some engines use a set voltage level to trigger as in the example posted at the beginning of this thread. These will have timing affected by air gap and RPM will tend to advance timing because the speed of cutting of the magnetic lines will be higher at higher RPM which equals higher voltage. Other systems use the reversal of current polarity in the trigger coil circuit to trigger. This is created by the movement of a north-south magnetic source across a coil.

Others use optical (rare today) and other variations of reluctance. One should read that "How it works" as an illustration of one strategy and not to conclude that this is how any specific system functions. Usually trouble shooting will be fine if following the scenario in the post but one may go far down the garden path in trying to adapt or change the system if one concludes that the wrong strategy for triggering is used.

As usual, things are more involved than indicated by magazine articles which are mainly intended for entertainment. Read any camshaft related web discussion and you will see what I mean.
 
#15 · (Edited)
CDI (which discharges a capacitor to obtain high magnetic flux increase) is common place in small engines while automotive tend to use magnetic field collapse because of the higher electrical capacity of automotive systems. Magnetic field collapse is the system used with breaker point ignitions powered from the battery. It is generally a bit simpler to avoid the use of the extra stator winding needed to create the charge current for the capacitor by using the DC power from the battery system.
I think whether a CDI is AC powered (as in the Generation 1 KLR650) or DC powered is a function of design decisions. While the older KLR650 CDIs are powered by AC from the stator exciter coils, some motorcycle CDIs are powered from 12 VDC, or battery power.

The complete CDI circuit in this latter case involves an inverter, converting DC to AC, a transformer, stepping up the consequent AC voltage, and rectification of this higher AC voltage to charge a capacitor. Further "downstream," the systems are similar (capacitor discharged across ignition coil primary winding to produce high voltage in secondary winding and resulting spark).

This information corroborated by the author of, "Understanding Stators" on ADV.

Basically, Generation 1 ignitions are capacitive discharge ignitions, and Generation 2 ignitions are inductive discharge ignitions, like our old points-condenser-coil ignitions. Each approach has its strengths and weaknesses.

I favor the Generation 1 ignition; as a minimum, the bike will run with a dead battery or without a battery at all. Generation 2 must have 12 VDC to run, either from an adequate battery, or sufficient output from the alternator/rectifier circuit.

As to implanting a Generation 2 ignition on a Generation 1 KLR650; better have a compatible ignion coil, along with the latter-day igniter. The resistance specifications of the two coils are considerably different, the Generation 1 coil functioning essentially as a transformer, and the Generation 2 coil primarily as an inductive device . . .
 
#17 · (Edited)
My earlier excitement about advance curves was misplaced....:t1204:

My thought was--I don't see how they would get spark advance with the circuit in the video. If Kawi left it out, think of the performance gains!

Doh! They didn't leave it out, as shown on page 210 of the holy book of Clymers. The fact that it's there & is probably about 30 degrees makes wringing another 50 hp ;-) out of the KLR beast unlikely.

Was trying to think how the CDI might generate that advance curve--needs another internal circuit/logic to provide a delay. I like the pickup coil voltage idea cause it would change nicely with engine speed. Must ponder.

Back in the '70s (1970's not 1870's) I had a timing light with the dial on the end. Those were the days. Wish I'd kept it and the '67 Olds 442 that I used it on.

Also in the 60's and 70's, there was quite a buzz in the DIY market for Transistorized Ignition. Actually CDI. They sub-optimized the system so you could use your old magnetic collapse coil. Would have worked better if they'd used a transformer coil like the KLR Gen 1

Another musing....I think the big difference in ignition design philosophy Gen 1-2 was the kick start possibility of the Gen 1. Maybe they sold it that way in some markets. No kick start and you might as well delete the exciter coil and run the ignition off the battery. Can probably get a few more watts out of the stator if you don't have to fool with the exciter coil.
 
#18 ·
I didn't recognize that you thought the KLR ignition lacked speed related ignition advance or would have clarified. It does have advance although I don't know whether the advance is air gap related, processor related or a combination. Some have claimed a modest improvement in the KLR from a programmable ignition module although not certain whether the claims were from someone who had actually done the work and measured or the more probable that it was from someone who read a magazine article and began to make claims based on this exalted expertise. ;-)

Most bike ignition advance is simply engine speed related, as I tried to describe earlier and this must assume maximum operating temperature conditions and wide open throttle since there is no way for the system to detect otherwise. My younger son has promised to lay out a processor for me which would allow ECT input, perhaps ACT, and allow an input engine load. Sorry, ECT = Engine Coolant Temperature; ACT = Air Charge (intake) Temperature. Not certain that this is worth the effort but part of that is that I'm becoming amazingly lazy.:t1204:

There should be a modest gain available through optimizing the advance curve for WOT (Wide Open Throttle) even if one ignored the ECT, ACT, and engine load factors. One must assume some consideration regarding emissions, as evidenced by the legal requirements at time of sale and of the exhaust cam retard & lean air fuel jetting.

A simple advance of the exhaust cam, re-jetting and remapping of the ignition advance should improve things. You will be well aware of those factors from your 442 experience.

While the improvement is unlikely be 50 hp ;-), some gain might be seen.

Mapping on top of that to improve partial throttle/partial throttle ignition curve might provide a nice increase in ride-ability and mileage.

I'm battling with some tubeless tire issues at present but might get to some advance work of son comes up with a platform which isn't too onerous to program.

I keep hoping that someone has done the work and will simply offer the simple and inexpensive solution.:fiddler:

Still, it might be out there. How many years before EM did the dyno work and posted the exhaust cam advance? Some must have known of that simply from having made a timing mistake.
 
#19 ·
The old 442. As a late teenage tuner I read the magazines and did stuff. I made it run much worse than stock so Dad made me put it back the way it was...

I've been looking at microprocessors and Arduino seems like the one for me. EZ software, lots of cookbook hardware and plenty fast processing ( I think) for the KLR. Could be wrong but thought the Megasquirt guys were using some variant these days.
 
#21 ·
Now, we all know that there has never been a dyno result that was significantly off, don't we?

"It's still unsolved", Tom said mysteriously.

Tom
 
#26 ·
I have re-read what you have said, many times, Normk!

And, I suppose I must agree with you, we are simply not communicating! :)

I've asked HOW advancing an exhaust cam 15 crankshaft degrees produces more power. You decline to discuss the mechanism (seems to me), instead stating as a FACT Kawasaki retarded valve timing for emissions purposes, sacrificing power, but . . . offer no provenance, no proof, no citation, no credible reference substantiating your allegation. May be so, but . . . where's the evidence?

I point out the stock exhaust valve timing, which as far as I know, hasn't been "retarded" for 27 inclusive model years (since 1987); I ask you to provide evidence exhaust valve timing has been retarded. No response, other than declaring valve timing specifications/data are essentially meaningless, in the arcane world of valve timing.

Conceivably, Kawasaki has been compromising power by retarding exhaust valve timing since 1987 for emissions purposes; if so, I'd expect the practice to be documented, somewhere. Generally, I think emission requirements were much looser in 1987 than presently.

On the contrary, I think IF advancing exhaust valve timing (ONLY) increases power output, a credible and plausible explanation exists for this result. Further, in my opinion, valve timing specifications have a useful place in engine design and tuning. My opinions, only. I respect yours.

=============

For some additional dimension in the discussion, does someone have a service manual with stock valve timing specifications for Generation 2s?

If so, please share exhaust valve opening (XXX degrees BBDC) and closing (XXX degrees ATDC) data.

Thanks!
 
#28 ·
In my understanding only,
Kawasaki Did Not Advance nor Retard the exhaust cam Timing on the Gen 2 or E series KLR for the 2008 and up years.
They Extended the Closing Ramp of the exhaust cam lobes, which Increased the Exhaust cam Duration and therefore Extended the Over-lap Duration.

As little as I understand hi-performance tuning vs low end Torque tuning, I'll try to give my understanding of the MC Mod.

By Advancing the exhaust cam only, we open the exhaust valves earlier and more importantly Close them Earlier.
By closing the exhaust valves Earlier, we get a Stronger Intake 'draw' or pulse.
By getting More Intake at a Lower rpm, we get a 'Torqueier' engine at lower rpm, but we May sacrifice some peak rpm potential and therefore peak HP.
IMU,only.

As Normk found on his personal Gen1 or A series, They Do Not all respond in the same manner. Probably due to mass production tolerances.

Just my understanding, guys .
 
#29 ·
I am also not able to offer more than to state what happens when valve timing is changed in a large variety of engines. I never intended to imply that Kawasaki offered one valve timing for the KLR and subsequently retarded that timing.

Just so we're clear, I'm not throwing stones so if it appears that way, that is not my intention. From working with marine and automotive engines from before and through the early emissions period, I observed several changes in valve timing which were directed to reducing emissions. That is what I stated and hope that have made this clear.

To return to my earlier example, if one were to take a pre-emissions Ford 429 engine, for example, the cam timing placed the index in line with the flywheel key. One can verify this with dial gauge as have done many times. When the 460 came under emissions (460 and 429 are almost identical), the noticeable change was that the cam index was placed 1/2 crankshaft tooth = 1 camshaft tooth ahead of the flywheel key. This retarded the valve timing by one camshaft tooth.

It was common practice for us to use a 429 timing set or to simply advance the camshaft of 460's by one camshaft (chain) tooth in order to "return" the cam timing to the pre-emissions point. This had the effect of increasing engine torque throughout the RPM range which also resulted in much better fuel consumption. We always had to reduce both curb (warm) idle and fast (choke) idle speeds following this modification which also indicated increased efficiency since idling at the same speed with smaller throttle opening (less air) can only come from improved efficiency.

Reflection as to the rationale for retarding (opening exhaust valves later) the timing will indicate that this increases the burning time for the combustion charge which will allow additional time for burning of partially burned fuel or CO. Running exhaust gas analyzers mapped this effect which was why some jurisdictions could not get through testing with the cam advance unless other things were done.

Checking with tune-up and emissions schools agreed with the scenario.

These effects were also seen virtually across the board with US engines of that era.

As I have said, it seems reasonable that Kawasaki followed the same course in developing cam timing which provided appropriate output, then finding that CO was high, were forced to increase burn time by the only practical means which was by opening exhaust valves later.

The KLR engines in which I have advanced cams (both Gen1 & Gen2) behaved as do various V8's and a number of ATV and other engines.

I have not run one on a gas bench but would bet a some donuts that taking an optimized air-fuel ratio KLR with advanced cam timing and comparing with retarded cam timing (exhaust) will see CO climb beyond the emissions limit.

Don't have to be right about this, simply offering the only case I have seen to explain the timing and rationale. If there's a better answer then I'd like to hear it as that would be interesting and possibly point to some opportunity.

Throwing valve timing numbers around without any justification as to their applicability is simply not useful. We saw many examples of the engineers not being able to predict the effects of various cam profiles to a useful degree. If they couldn't use these numbers to predict effects to a useful degree.....

We do know:

1) The KLR has been subject to emissions standards in some markets.
2) The reaction to advancing the exhaust cam is similar to other engines subject to emissions.

So, failing it seems reasonable that the pattern fits.

In fact, increasing emissions levels have apparently encouraged the addition of exhaust air "injection" which would serve to reduce CO and possibly HC levels.

I'm done with this subject because it seems only to go round and round. Perhaps that's my doing and if so I apologize for the band width.
 
#30 · (Edited)
Thanks for the Generation 2 valve timing info, Tom Schmitz!

Generation 1, EV open 57 degrees BBDC; close 31 degrees ATDC, 268 degrees duration.
Generation 2, EV open 57 degrees BBDC; close 37 degrees ATDC, 274 degrees duration.

Thus it appears the exhaust valves stay open longer, close later in the cycle, with Generation 2 vs. Generation 1 (by 6 crankshaft degrees, the amount the duration was extended). Exhaust valves open at the same point for either generation.

Don't understand how leaving the exhaust valves open longer reduces environmental pollution, but by some complex interactive relationships, perhaps this is so.

And, advancing the exhaust valve timing 15 crankshaft degrees while subtracting 15 crankshaft degrees from valve overlap may indeed deliver a 10 % power increase across the rpm spectrum.

Regardless, I appreciate the conscientious effort to explain how this might be the case, from those who have discussed the issue on this thread. Thanks for the interesting possibilities raised, guys!
 
#33 ·
I addressed the quoted comment from this thread, pdwestman:

Originally Posted by Normk:

A simple advance of the exhaust cam, re-jetting and remapping of the ignition advance should improve things.
I've wondered how advancing the exhaust cam (only) increases power output.

No objection to discussing the issue in another thread, or . . . NOT discussing the issue in another thread! :)
 
#32 ·
One question I had earlier was how can an analog CDI provide an advance curve? One answer I ran across on the all knowing Internet--use an "all pass" analog filter.

Ideal All Pass filters (as I was reminded by my papyrus copy of "Signals & Systems") don't attenuate signals, they just delay signals (shift phase) as a function of signal frequency. E.g. As the RPM goes up, the timing signal gets shifted.

AP filters can be made from a nightmarish combination of a ladder of RC filters and/or a network of choke coils (inductors).

Now I really, really want to cut a CDI apart
 
#34 · (Edited)
One question I had earlier was how can an analog CDI provide an advance curve? One answer I ran across on the all knowing Internet--use an "all pass" analog filter.

Ideal All Pass filters (as I was reminded by my papyrus copy of "Signals & Systems") don't attenuate signals, they just delay signals (shift phase) as a function of signal frequency. E.g. As the RPM goes up, the timing signal gets shifted.
My guess also at the spark advance technique, Uncle Wray. The "signal frequency," relating to the pulse rate from the pickup coil, a function of engine rpm.

If so, a simple module could be crafted by a competent electronics technician to alter the spark advance curve, I'd think.

Hey, FREE POWER! Advance your KLR650 spark timing! He'd sell a million of 'em, and . . . some valid, demonstrable, repeatable power increase might actually be available from tweaking the ignition map. (Might have to use high-octane gasoline to reap this bounty (avoiding pinging, "knock"); true KLRistas would not like to pay extra for the high-test fuel! :)).
 
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