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Discussion Starter #1
I have a question regarding the newer style CDI units. I have a 1981 cm400t custom that I believe the TIa01-20 CDI died, as I have a no spark situation currently. I have ohmed out the coil incoming and outgoing and tested ok. I think I also seen the ac trigger wire putting out voltage as well. I also ohmed out the kill circuit and it also was ok. My problem is that the old CDI are not cheap and in a used crappy looking condition for around $100. I thinking that I can adapt a newer Chinese made one with dual CDI’s and coils and only pay around $40. Has anyone tried this yet? I am an electrical Automation tech by trade and feel confident in my skills. I have also been working on Motor cycles and engines for many years now. Thanks for any input in advance.
Brandon
 

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There's a technical explanation of how this CDI system works in the Technical Features section of the FSM. No one has attempted this to my knowledge and I doubt it it will work. But nothing ventured, nothing gain so I'd say go for it.
Used CDI's are a gamble, some good some bad. CDI Magician on eBay sells his units for $80-100 usually, Rex's Speed Shop in the UK sells his for @$145 shipped to the US.
Did you run the all the tests in the Igntion Diagnosis thread? https://www.hondatwins.net/forums/6...400-450-cb450sc-manual-trans-1978-1986-a.html
There's another option for the ignition system that uses an Ignitech ignition module that's programmable and only utilizes the primary pickup from the stator ass'y.
 

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Well there has to be an answer out there, some other CDI from another bike can be adapted and have a functional timing advance.

I was looking at the 250 Nighthawk wiring earlier, I wonder if the CDI pulse is similar enough?

It sounds like you have the skill set and the motivation, I'll wish you good luck in your search.
 

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Discussion Starter #4
Having a functional timing advance might be a problem

Having a functional timing advance might be a problem. I would wire the trigger input to the primary stator wires BN and LT Blue!?. I believe the newer CDI"s have this feature built in.?

universal-modified-motorcycle-motorbike-atv-scooter-moped-igniter-ignition-racing-digital-adjust.jpg :confused:
 

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The GM ignition module has been tried a couple of times, works well to get the engine running BUT the timing is fixed since there's no timing advance. Without the advance the engine runs poorly after @3-4K.
I don't know anything about the newer CDI systems being used. I've been running the Ignitech for several years now with no complaints
 

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Agreed, without some sort of ignition advance it's not a solution for the 400/450 series.
Here's a little more reading on the topic if anyone is interested: http://forums.sohc4.net/index.php?topic=53773.0

I'm following this with an eye toward the CB250 Nighthawks, i'm off to check the FSM to see how that engine takes care of timing advance.
 

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Well as it turns out the 250 Nighthawk and Rebel use a fixed pulse coil as well. Perhaps that system can be adapted?
 

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I've been suggesting using those parts for the CM200T bikes since there are no CDI's available it seems. Every aftermarket listing for the CM200 doesn't work.
For the 400/450 it would need the stator, rotor, CDI and coils assuming the stator and rotor will fit the engine. That's not a cheaper alternative which is where this topic started. Not sure there's anyway to change the 1950's electrical design of the system.
 

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CM185s and CM200s do have a mechanical timing advancer, so the 4-pin GM HEI module would work perfectly. The link in reply #7 is a thread over on SOHC4 by Pinhead, he's a member here under the same name. The thread states that the relucters from the CB650 or practically any other early 80s Honda can be mounted to the points plates of earlier bikes, and together with a working centrifugal timing advancer would work correctly with the HEI module.
 

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For the 400/450 it would need the stator, rotor, CDI and coils assuming the stator and rotor will fit the engine. That's not a cheaper alternative which is where this topic started. Not sure there's anyway to change the 1950's electrical design of the system.
From looking at the parts diagrams and FSMs I'm guessing the 250 stator and rotor won't bolt on directly to a 400/450 series engine, the 250 rotor is open on the left side and the stator mounts inside the left engine side cover like a SOHC CB750 is set up.

But if I go to the 400/450 ignition troubleshooting thread and compare the resistance readings listed there with what I measure on the three 250 engines I have...maybe we can gain some ground.
 

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Here are my comparison notes:
(All 400-450 values are sourced from https://www.hondatwins.net/forums/64-electrical-discussion/50457-ignition-diagnosis-cb-cm-400-450-cb450sc-manual-trans-1978-1986-a-2.html All CB250 Nighthawk values come from the FSM that is available from LDR)
400/450 Ignition
troubleshooting thread
VS.
250 Nighthawk FSM

Ignition coil primaries
-400-* 0.35 to 0.55 ohms
Yellow and Green wires.
One coil with 2 plug leads.
-250-* 0.1 to 0.3 ohms
FSM says Bl/Wh and Green wires.
Two separate coils, primaries* connected in series.
(See the diagram at the end of this post)
Ignition coil secondaries
-400-* 7.2k to 8.8k w/o plug caps
-250-* 2.8k to 3.4k w/o plug caps
(250 measure at green primary to H/T lead)

-400- Brown and Light blue wires, This is the primary pickup coil, the aluminum piece outside the rotor.
203 ohms.
-250- Ignition pulser
Blue/yellow and Green/white.
50 to 170 ohms.

-400- This is the CDI power source** White and Blue wires
84.2 ohms (big coil on stator)
-250- Exciter coil
Black/Red and Gnd.
50 to 180 ohms (big coil on stator)

Alternator test
-400-* yellow to yellow to yellow 1ohm
Yellow to Gnd = infinity
-250-* yellow to yellow to yellow
0.2 to 0.6 ohms
Yellow to Gnd = infinity


-400-* Pink and Green wires.*
This is the advancer pickup sensor.
129 ohms.
There doesn't seem to be a corresponding part I can find on the 250 is this function handled electronically by the CDI?

 

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My thought on the newer system is that advance may be voltage controlled. As the engine spins faster the exciter coil will generate higher voltage and possibly there's a programmed chip inside that alters timing in relation to that voltage. The lack of specific information on the system is a booger.
 

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I had read somewhere that the timing was actually electronically retarded and that at 3000 RPM the timing was "advanced" so to speak from there.
I'll have to see if I can find more on that.

I'm also waiting for the OP to weigh in.
 

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Discussion Starter #15
Thanks for all the research you have done, I believe this could be beneficial for many other twin people if we can figure the out. So my bike currently isn't at my house so working on it is some what difficult. My bike is currently in my father in laws Shop staying out of the elements. I did manage to get over there this weekend to try and go through the ohming out test again. The numbers I was reading are all close to what has been listed ( left my reading at home this morning). The only thing that was off was the coil output with the resister caps on was at 18k ohms. I then got excited an put a battery on the bike removed the resistor caps and boom no spark still LOL. so i am still leaning towards the CDI. I have all the parts I will need to do this swap as i also have a clone rebel 250 in my quad that i can still the parts off of to test functionality. the other thing iv'e been wondering is there a kick stand sensor that might be causing my no spark problem. I'm not seeing one and my key and kill switch also seem to be good in testing them. I probably should get my bike home to start doing my research. I also was thinking of doing the GM modulator just to get it running as iv'e never herd it run yet . this only sounds like a temporary solution also.

Thanks Brandon
 

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There's no kickstand switch on the manual trans bikes, that's only on the A model.
The coil resistance test is done w/o the caps in place, looking for 7.2K to 8.8K ohms. Caps are supposed to be 5K each.
The design of this coil setup is that one plug wire must be connected to an installed spark plug while checking for spark with the other wire. Both wires disconnected will result in no spark.
 

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Some other differences I noticed between the 400/450 and the 250 Rebel/Nighthawk, the 400/450 has 6 magnets on the rotor, the 250s only have 4. And the 400/450 redline is nearly 1000 RPM higher than the 250.
 

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Just looked at the 1996-2000 Rebel FSM. Full advance is 25 degrees, 20 degrees less than the 400 so even if this is made to work the engine will be lacking power
 

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I was afraid of that. What's full advance on the 400A/450A engines? Maybe it'll help there?

I think it's of value to explore until a solution is found or all possibilities are discounted by comparing printed specifications. Thankfully Honda has only built another hundred or so twin models... Let's start with the Hondas, and probably narrow the field by Degree of Advance, the 400/450 full advance is 43* BTDC +/-2* at 4500 to 5350 RPM
(please correct if I've misstated)
 

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The 400/450 A models have the same timing spec as the manual transmission version. 43* +/-2* at 4500 to 5350 rpm
 
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