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Author Topic: 2 CDI's on one motorcycle  (Read 792 times)
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Croatia
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Hi all!

I have the 2 stroke motorcycle which have restriction on CDI and stator which couldn't be removed. Problem is that CDI is also responsible for controlling the valve in the exhaust. And I've come up to the idea, to buy cheap DC CDI frome some scooter nd use that CDI for creating spark and leave original CDI to control the valve.

Thing what I don't know, is: should I put output for ignition coil from my original CDI to ground, and should I do that using the resistor, and would that thing work, or it will be there some white smoke?

Thanks!
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Denmark
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Ask in a motorcycle forum, we have no idea of the electronics on a Motorcycle...

// Per.
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Canada
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@Zapro
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...we have no idea of the electronics on a Motorcycle...
Speak for yourself.


@jocoj100
A few questions:

1) Which motorcycle are talking about?
2) What is wrong with the current CDI unit?  Is it not producing a spark?
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I think he is trying to bypass the rev limiter on his bike.  I heard some are easy to bypass(not sealed?), some people also buy an unrestricted CDI.(like from ebay)
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Ahhh, makes sense (actually, not very sensible).  Then he would leave the output that normally drives the coil floating, not grounded.

However, if this has an electronically controlled exhaust valve, then the operation of that valve must be properly timed with the ignition advance curve, or there will be no advantage to adding a 2nd CDI.  In fact, it would more than likely cause the bike to run slower.  2-stroke rev limiters work by retarding the ignition slightly at an RPM long after the engine can make maximum power anyway.  There is just no sense in defeating it.

My son is a national pro level off-road rider.  We have never even dreamed of trying to defeat the rev limiter on his bikes, and yes, he does ride 2-strokes.  Not even the top Supercross riders ride without rev limiters.  They even ride 4-strokes where the rev-limiter just cut's off the ignition altogether and still they are not tempted to defeat it.

I can't see any reason to go that route, not even on a street bike or a road racer.

This seems like an ill-advised modification if that is what the OP is trying to do.
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Croatia
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Ahhh, makes sense (actually, not very sensible).  Then he would leave the output that normally drives the coil floating, not grounded.

However, if this has an electronically controlled exhaust valve, then the operation of that valve must be properly timed with the ignition advance curve, or there will be no advantage to adding a 2nd CDI.  In fact, it would more than likely cause the bike to run slower.  2-stroke rev limiters work by retarding the ignition slightly at an RPM long after the engine can make maximum power anyway.  There is just no sense in defeating it.

My son is a national pro level off-road rider.  We have never even dreamed of trying to defeat the rev limiter on his bikes, and yes, he does ride 2-strokes.  Not even the top Supercross riders ride without rev limiters.  They even ride 4-strokes where the rev-limiter just cut's off the ignition altogether and still they are not tempted to defeat it.

I can't see any reason to go that route, not even on a street bike or a road racer.

This seems like an ill-advised modification if that is what the OP is trying to do.

That is what I need!

Let me explain.

Bike is Yamaha TDR 125.

Problem with my bike is that it naturaly have about 30 hp, but it's bought in Germany and there all similar bikes are restricted to 15hp so that you can ride it with 16. But in my country there is no such a rule.

Problem is in the CDI and the stator, cdi retards ignition a little bit, and stator gives weaker pulse also.

So I'm planing tu put the DC CDI which works on 12V for spark. I would leave everything as it is now, but only split the wire which comes from trigger and one pole connect to the old CDI and other one into the DC CDI. And leace output from original CDI floating?

Would this work?

Thanks!
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Canada
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I think it would work, but not very well, especially in the mid-range.  It is not likely that the advance curve will match the engine, exhaust, carb, or the power valves.  2-strokes are a tuned system.  You can't just make dramatic changes in one area and not make matching changes elsewhere.

Have you looked into other alternatives like using a YZ125 or KTM 125 ignition, or is the TDR produced in other countries with more power?  What about the UK version?
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You should really try a Yamaha forum, like this - http://yamahaclub.com/forums/topic/32206-derestricting-yamaha-tdr-125-2000/
... there seems to be several things to do depending on year.
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Yes, and in particular listen to the the post form Cynic.  If you want a faster bike, sell the TDR and get a bike that comes unrestricted.
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Croatia
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I think it would work, but not very well, especially in the mid-range.  It is not likely that the advance curve will match the engine, exhaust, carb, or the power valves.  2-strokes are a tuned system.  You can't just make dramatic changes in one area and not make matching changes elsewhere.

Have you looked into other alternatives like using a YZ125 or KTM 125 ignition, or is the TDR produced in other countries with more power?  What about the UK version?

2 strokes doesn't need advance curve, most of them have fixed ignition like my Yamaha wheri it's 17 degrees BTC.

I already put the DC CDI on my bike, and it worked but problem is that my bike have valve in exhaust which gives him power at low rpms so with only DC CDI it goes grat above 6.5k rpm, but below is literally dead.

So my biggest concern is can I just leave wire which goes to ignition coil from original cdi unconnected and would that burn CDI, because cdi is very expensive I didn't wanted to try this before asking somebody who knows something about that!
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Canada
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2 strokes doesn't need advance curve, most of them have fixed ignition like my Yamaha wheri it's 17 degrees BTC.

No true, not true at all.  Not since about 1980.  All my Husqvarnas and KTMs have advance curves.  Every 2T bike I've owned since my 1981 IT250 has had an advance curve.  You are very much misinformed my friend.

So my biggest concern is can I just leave wire which goes to ignition coil from original cdi unconnected and would that burn CDI, because cdi is very expensive I didn't wanted to try this before asking somebody who knows something about that!

You can do it, but it's not going to work very well.  It will not burn the CDI but it will run like maird.

My advice is that you DO NOT do this.
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Croatia
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2 strokes doesn't need advance curve, most of them have fixed ignition like my Yamaha wheri it's 17 degrees BTC.

No true, not true at all.  Not since about 1980.  All my Husqvarnas and KTMs have advance curves.  Every 2T bike I've owned since my 1981 IT250 has had an advance curve.  You are very much misinformed my friend.

So my biggest concern is can I just leave wire which goes to ignition coil from original cdi unconnected and would that burn CDI, because cdi is very expensive I didn't wanted to try this before asking somebody who knows something about that!

You can do it, but it's not going to work very well.  It will not burn the CDI but it will run like maird.

My advice is that you DO NOT do this.

Then I was wrong, but that isn't matter here, because I will buy DC CDI from some other motorycle so it probably has programmable ignition. But that isn't matter, because I was made CDI according to this schematics:
http://mastercircuits.blogspot.com/2010/07/yamaha-dt125-cdi.html
And that CDI have fixed ignition curve, and I didn't notice any performance loss, also I was put CDI from some four stroke scooter which have advance curve and performance was the same.

But main thing is that I'm not gonna destroy CDI, so that is good. I will see is this work!

Thanks!
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