Kokusan Blues

[buzzard]

I have some recent experiences that I hope help someone else. I had one of the devil bikes (2002 250xc) that I just couldn't jet. It started and ran fine right up to mid-range, then refused to take throttle, and wouldn't rev out. It turned out to be ignition problems. I put a timing light on it, and it had the wierdest advance curve you could imagine. Right above idle, it jumped to full advance, then about midrange, it went back to no advance. I always thought that a CDI either worked, or it didn't. I was wrong!


I used an inductive timing light. It uses a pickup that clamps over the plug wire, and any old 12v battery. I put the piston at TDC, and marked a line on the rotor, and a corresponding line on the engine case. Using a dial indicator, I also marked a line on the engine case representing 1mm BTDC.


I was fortunate to find an ignition on this site, in the For Sale forum. When it got here, I installled it and checked it's advance curve. I wouldn't call it a curve, exactly. Just above idle, it went from no advance to full advance. It stays at full advance until the engine returns to idle. Actually, my 250 runs great with this ignition. I wondered if this was normal. I have a friend with a 2006 300EC. I went over to his house, timing light in hand, and we checked his bike's "curve". My friend has never been able to get his bikes top end jetted correctly. It has never had that top end rip. Well, his ignition started at full advance, right at idle, and smoothly went back to no advance as the RPM increased. BAD IGNITION!


My friend ordered a new ignition. They go $300+. When it got here, we installed it. It is different than mine, in that mine uses 7 wires to connect to the wiring harness, his uses a multi pin plug. Looks like the same unit otherwise. We timed it. It has the same curve (or lack there-of) as the used unit I purchased. Right above idle, it jumps directly to full advance, and stays there. His 300 now runs great. The top end rip is there. He never even thought he might have a bad ignition. He's been jetting it for about a year.


Here is an odd side note. I searched kokusan on eBay. Up came shifter kart ignitions, by Kokusan. I bought one for $50. It has exactly the same wiring harness as my Gasgas ignition, same colors and connectors. I installed that one, and guess what? The same advance "curve", and it runs great. It is a black box (hence the name, I guess), about 3"x4"x3/4". I mounted it to the rear fender.


So I guess the take home message here is to put a timing light on your bike. It's quick and easy to do, and you may just find out a lot. Also, it pays to set your initial timing. I had to slightly modify my stator plate to allow it to rotate enough to set the timing at 1mm BTDC.


If anyone has knowledge of different advance curves, or ignitions, I would like to hear about it. I'm going to check another friend's 2005 KTM 250EXC soon, and see what Kokusan sells to KTM. I am a little disappointed in the lack of technology in the ignition on these 2stroke GasGas bikes. I have to wonder how they might run with an ignition that actually has a curve, in that it advances continuosly as the RPM increases. Thanks, Buzzard

 

[GMP]

I did the same thing on my '03 EC250, and your right it advances quick and stays there until the revs drop. I was trying to see if I could tell a difference between the OEM CDI and one from an '00 XC250 that gave better low and mid power. I could not, using this crude visual method, but there was definately a difference in performance. I did not have a tach, and I did not rev the bike full out. I think what appears to be an instant advance is actually a curve but one with limited resolution over a narrow RPM bandwidth. It would depend on the processing power of whats in the CDI box. Also, with no load (I'm assuming you just reved the bike in neutral like I did) its easy to blow through this RPM range. With the bike on a dyno with a tach you could probably learn a bit more. The trigger pulse is actually received by the CDI at or greater than max advance (deg BTDC), and the box acts as a variable delay device.

If I could power the CDI from an external source, and had the time to do so at work, it would be fairly easy to set up a test rig with a PC and some I/O hardware I have to trigger the input and wait for the output, at the full range of simulated RPM, and plot the time delay (advance curve).

Theoreticly the curve should advance up until the peak power and then retard in the "overrev" range. If your interested in this Google it there is a lot of info especially related to tuning 2-stroke road race bikes. Its nothing like a 4-stroke. Interesting stuff.

BTW, the CDI with the multi-pin connector is the newer dual map unit, used on some '06s and up.

 

[2 strokes 4 life]

I have heard that the XC250 bikes and EC200 ignitions have a more avdanced curve that gives you more power.

 

[blitz11]

What was your source for that ignition? FOr $50, it might be worth having a spare.

Thanks.

blitz

 

[Skidad]

Great info buzzard and GMP

I have a hunch the KTM will be the same but please do test that as well. I also wonder if various KTM boxes would work on the Gassers. They have quite a few different ones for sure.

It seems kind of odd to me in my relatively short time on the GG site that these bikes seem to have far more ignition issues than the KTM's. I have been a member on the KTM Talk site for years and just don't recall seeing so many ignition issues as the Gassers and the volume of bikes is HUGE over there.

 

[2 strokes 4 life]

Well come to think of it, dont most bikes use a kousan ignition? Mabe I can get some of my friends bikes ignitions and see if there are any gains.

 

[jiauka]

Take a look at this:
http://www.sportdevices.com/ignition/ignition.htm
that guy has made a DIY CDI and a test machine. I'm thinking about doing something similar with a small USB microcontroller like the ATMEL AT90USB162.

have fun,

j.

 

[gasgasman]

On the 24hr Perry Mountain bike we built last year, the lighting coil and CDI module came off a KTM.
The stator plate had to be advanced a lot more that the GG stator plate.
The bike never really reved out like the GG stock CDI unit.

 

[widebear]

I'm curios to know what full advance under load would be. I like run a little more static advance, 1.5 degrees for crisper off idle perf, would be nice to know how far you could go on pump gas without courting pre ign? Production tolerances vary so much on mass produced items theres prob thousands of defective ign's in circulation.Back in the day when I was involved in stock car racing a 500 cfm carburator rule was put in to place. We flow tested over 30 new out of the box Holly 500 cfm two barrels. The best one, the keeper, flowed 600 cfm the worst 425!

 

[GMP]

Take a look at this:
http://www.sportdevices.com/ignition/ignition.htm
that guy has made a DIY CDI and a test machine. I'm thinking about doing something similar with a small USB microcontroller like the ATMEL AT90USB162.

I saw that. While very interesting for research purposes, you would be hard pressed to eaisly implement it in a package that would survive on the bike. It would be neccessary to find an appropriate enclosue and potting material. Also, you have no idea of its suseptability to EMI/RFI.

If I had the time I would do it a different way. I would implement the test CDI as an interface only, and use a computer and my own software to control the prototype ignition and develop the proper map or maps, on a dyno. This would then be implemented in a microcontroller and properly packaged.

As far as ignition issues with GGs, how many of those are verified? I don't think a GG Kokusan is any different than a KTM Kokusan as far as reliability. IMO, if its a real ignition problem, it may be more of an issue with connections, grounding, wire lengths, etc. on the bike that may make it more prone to EMI/RFI issues. Also, maintanence can play a part. I see so many pics of flywheel/stators that look like rusted shipwrecks, and can only imagine what can happen as far as current leakage paths across the internal connections and the effect. FWIW, no GG I have had or worked on has had an ignition problem. I do however, on a new bike, go through the electrical system. The ignition is always clean and dry as well.

I've been doing this stuff for a long time and have seen a lot of strange things with various pieces of instrumentation and equipment.

 

[blitz11]

I had a Honda CX500 which used a CDI. After 25 years, the capacitors went bad, and the ignition failed. Honda wanted $400 for the CDI box, which was probably more than the bike was worth.

I found on the web someone who had taken a CX500 cdi apart, and figured out the layout. For a hobby for a while, i built tube guitar amplifiers, so i took out my circuit board equipment, laid out, and built a CDI. I used a potentiometer to bias the thyristor so i could set the advance break point.

I built 2 for $25; one to use, and one as a spare.

I sold the bike, but the first ignition is still working with the new owner. Granted, it is a street bike, but as a point-to-point circuit, it has yet to fail. Using a big thyristor was key; it can dissipate heat, which keeps everything happy.

My guess is that because one can choose one's parts here, you could build a reliable ignition for not too much $$$. You can buy an enclosure and potting material, and if you're worried about EMI, you can do two layers of potting with the layers separated by foil.

But, I never had RFI/EMI problems with the CDI i built, and it was just a single board in a project box with NO potting. I don't see that as much of an issue.

This is all great information. Excellent work on Sport devices. That's REALLY great.

Thanks.

blitz

 

[GMP]

That was almost certainly a basic analog unit, plus, the 12V source on a street bike is nice and clean (the battery is a great capacitor). Not much to screw up in there. Now with digital powered by a magneto coil, its another story. Power/signals must be clean within certain thresholds. Poke around on a bike like the GG with an oscilloscope and you will be horrified. I would bet that the OEM CDI has a well thought out supply circuit, and the inside of the enclosure has metalized coating for sheilding.

I'm not saying to anyone don't do it, I think its great to experiment with this stuff and learn something. I just want you to be aware that there are more things to be considered for a good result.

 

[blitz11]

Good points.

1. Actually, i like the guy's idea about running it "total loss" off of a battery. That in itself eliminates power supply problems. I've not put a scope on my GG.

2. The secret to good audio (guitar, audio amps) lies strictly with the power supply. if you have a junk power supply, you have a junk amp. probably the same thing here....my guess is running total loss is the optimal.

3. I don't think that the CDI as drawn would be susceptible to or generate that much EMI/RFI. The power supply might cause issues with the PIC, but the external battery would eliminate that.

4. If you don't want to lay out $350 for a CDI, and you're handy, it might be worth doing. I might build one this winter and see where it takes me. Or I'll just hope my ignition lasts. PICs are easy to program, so building your own advance curve is all up to you.

This might make for a good "tech article."

Thanks for the follow up.

blitz

 

[GMP]

There are ways around the supply issue without going to a battery, you just have to understand what you are dealing with as far as noise.

Back in the mid '80s I built my own enduro computer prototype. It was fully programable like an ICO and had an LCD dot matrix display. It was based on an Intel 87C49 micocontroller and Dallas smart clock, and coded in Intel Assembler. It basically worked on the bench with simulated inputs. The KDX200 bike supply was too dirty so I went with a battery but the consumption was quite high with the ICs back then. I got laid off from that company and lost after hours use of the development system/emulator so I was never able to finnish it. That stuff was big $$ back then.

 

[jiauka]

Poke around on a bike like the GG with an oscilloscope and you will be horrified.

100% true, I was about to connect my Garmin GPS using a simple diode bridge an a large cap, and I checked the output before connecting my garmin, and I was really horrified and I ended up with a bridge+cap and a DC/DC converter to get a clean signal. A similar aproach can be done on a DIY CDI. I do have experience with EMI/EFI microcontroller problems, a good separate digital ground and a shielding solves 99% of the issues.

If I have a spare weekend without any broken leg or arm I will try it.

have fun,

j.

 

[GMP]

I ended up with a bridge+cap and a DC/DC converter to get a clean signal. A similar aproach can be done on a DIY CDI.

Thats exactly the way I would go, and I suspect whats in the Kokusan. I would also isolate all external signals.

A lot of my experience comes from designing medical lab instrumentation for BD, primarily blood cell counters. These instruments have very high gain analog systems as well as microcontrollers, plus pumps, valves, and other noisy components. Also spent a few years at a TUV office here in the USA. And you?

 

[iancp5]

This is quite an interesting thread.
I wonder if it accounts for the some GG's don't idle properly issue? Also the fact that whatever I did with my 300 it was too abrupt in power coming in from idle. All the time people telling me the 300's a pussycat! I gave up trying to get a reliable idle or a smooth enough power entry for our wet and slippery enduros and bought a 200.

The 300 always felt to me as soon as I came off idle, wallop a load of torque appeared and would spin up in wet conditions. Turning on wet grass was a nightmare.

 

[GMP]

The CDIs do have different curves. They vary by year and displacement, some years the 250s and 300s having different curves. The 300 can be more of a beast with a 250 CDI. My '03 250 was a bit of a dud off the bottom until I swapped in an '00 CDI. Maybe your bike started life as a 250 and was converted to a 300 at the factory or importer, its been done here.

 

[jiauka]

A lot of my experience comes from designing medical lab instrumentation for BD, primarily blood cell counters. These instruments have very high gain analog systems as well as microcontrollers, plus pumps, valves, and other noisy components. Also spent a few years at a TUV office here in the USA. And you?

I use to design medical monitoring equipment, now I'm doing digital TV systems that need to be ON 24/7, I guess you already know the related software+hardware problems on a system that needs to be allways ON, in some way a CDI has the same issues + the radiation problem and the harsh environment, but with modern SMD technology this is not a big problem.

have fun,

j.

 

[GMP]

Cool. If you experiment with the ignition idea keep me posted. I don't have a lot of electronic fabrication resources where I work now. We do custom process control stuff for our own use so its primarily buying subsystems and doing the software.

Good Luck.