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Need help... can i run a KWOB 8513 Nt400 cdi in a honda cbx750 rc 17

1652 Views 48 Replies 6 Participants Last post by  Classic250
Need help on wiring ... it has 4 pins adjacent to a 5 pin ...
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I like electricity and speak wiring schematic but I would need to start with a wiring schematic of the original bike and the donor bike too.
I looked at the honda cbx750 rc 17 wiring and the 5 wire connector is coming from your alternator
the 4 wire connector is coming from the pulse generators to the CDI on both bikes and those might be close enough in concept to work, but I would check the service manuals for both those machines and see if the ignition coil resistance is the same. Wiring diagram implies it's the same part, so I'm optimistic it will work.
I like electricity and speak wiring schematic but I would need to start with a wiring schematic of the original bike and the donor bike too.
I looked at the honda cbx750 rc 17 wiring and the 5 wire connector is coming from your alternator
the 4 wire connector is coming from the pulse generators to the CDI on both bikes and those might be close enough in concept to work, but I would check the service manuals for both those machines and see if the ignition coil resistance is the same. Wiring diagram implies it's the same part, so I'm optimistic it will work.
Thanks for that. I do have the wiring schematics for both too. Alterntor? Maybe I just don't know how to read the wiring diagram but I dnt see any wires commin from it. NT600 is a vtwin and do you think it would make an inline fire up?
I like electricity and speak wiring schematic but I would need to start with a wiring schematic of the original bike and the donor bike too.
I looked at the honda cbx750 rc 17 wiring and the 5 wire connector is coming from your alternator
the 4 wire connector is coming from the pulse generators to the CDI on both bikes and those might be close enough in concept to work, but I would check the service manuals for both those machines and see if the ignition coil resistance is the same. Wiring diagram implies it's the same part, so I'm optimistic it will work.
I think you were looking at the regulator rectifier. 3 yellows and 2 wires black and white from the field coil. Cdi got 9 pins. Schematic says 4pins and 6pins goes in out the cdi.
I looked at everything :geek:
Wiring for the NT shows a 3 wire output from the alternator, that means it has no brushes and no exciter coil.
http://hawkworks.net/manual/images/19/wiring-diagram.gif
The diagram for the RC17 shows that it has an exciter coil in addition to the 3 phase alternator outputs. that means it has carbon commutator brushes that energize a 4th. coil which is a completely different type of alternator.
http://teamrc17.net/teamrc17.net/files/CBX-wiring.gif

Alternator feeds the battery charging system in both these motorcycles, they do that through a rectifier/regulator which is very different between the 2 motorcycles. The alternator/regulator/rectifier assembly is Not part of your CDI. Both engines have 2 pulse generator coils to control spark timing and while one engine is a twin and the other a 4 cylinder they are both fitted with a total of 4 plugs firing in pairs, the NT has 2 plugs per cylinder.

The pulse generator signals the "spark unit" which is the CDI (Capacitor Discharge Ignition) and those appear the same in both diagrams (4 wires in & 4 wires out). The 2 ignition coils have a very low internal resistance and for the CDI units to be compatible I would expect the ignition coils on both those machines to be the same or similar in power draw. If the ignition coils have the same internal resistance, they likely are interchangeable and so would be the spark units powering them.
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On the NT
The 3 yellow wires are your 3 uncontrolled AC outputs each out of phase to one another, on the NT the R/W(red-white) & G (green) wires coming from the rectifier/regulator is your rectified 12 VDC output. Magnets inside the alternator are permanent type so no exciter coil or brushes are required.

On the CBX
The 5 wire connector with 3 yellow wires each having AC output similar to the NT, but on the CBX the other 2 wires (white and black) are to energize the alternator exciter coil, the CBX alternator has an electro magnet instead of the permanent magnets used in the NT and the exciter coil powers an electro magnet inside the alternator.

The connectors on both 'spark units' have 4 wires in and 4 wires out, but one connector is a 6 pin connector that only uses 4 pins so that you don't connect to the wrong one by accident.
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CBX alternator charging circuit:
(either works now or needs service to charge your battery)
Slope Font Rectangle Parallel Diagram


CBX Ignition system:
Rectangle Font Schematic Line Parallel

... there is a small error on that diagram in the way they draw or tag the 4 and 6 pin connectors

NT ignition circuit from your NT donor machine: (virtually the same)
Product Rectangle Font Line Slope
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3
TR why do you keep talking about the charging circuit? He only asked about the CDI/ ignition circuit (which you also touched on).
TR why do you keep talking about the charging circuit? He only asked about the CDI/ ignition circuit (which you also touched on).
Because he is using 'number of pins' to describe connections that can only relate to the charging circuit. That has little to do with the ignition circuit which is the CDI part.
Because he is using 'number of pins' to describe connections that can only relate to the charging circuit. That has little to do with the ignition circuit which is the CDI part.
I don’t see where you got that. The charging circuit you posted has a 6 pin and 4 pin connector. Not a 5 pin. But I see no 5 pin connector anywhere, so I don’t know how you jumped to that conclusion.

But anyway, I’d be more wary of the fact that the two CDI circuits you posted show the 6 pin connector wired to the pulse generator on one bike and on the other bike it’s the 4 pin connector wired to the pulse generator. You noted that you thought it was a typo, but I’d be mor inclined to think it was a way to make the CDIs model specific. OP, I’d make sure the wires to the pulse generator on both bikes actually go to the same connector.
I don’t see where you got that. The charging circuit you posted has a 6 pin and 4 pin connector. Not a 5 pin. But I see no 5 pin connector anywhere, so I don’t know how you jumped to that conclusion.
...
Where did I get 5 pin connector from -> his first post:
Need help on wiring ... it has 4 pins adjacent to a 5 pin ...
8Ball you see no 5 pin connector anywhere? -> then you are not looking at the wires coming out of the alternator in the diagram I posted. There are 5 wires required in the alternator connector and that part is also indicated as a 6 P connector on the drawing.
If the "wiring ... it" has a 5 pin connector logically that would be connected to the alternator which requires 5 wire connections, the 'spark unit' didn't grow and extra connection, that component is faithfully shown with 4 wires in and 4 wires out on both engine spark units.

Why should the spark unit interchange:
His original engine has 2 pulse generators the donor has 2 pulse generators.
His original engine pulse generators (2) are in turn connected to 2 ignition coils that are in turn connected to a pair of spark plugs (2) that fire simultaneously. By the schematics I sourced, the donor circuit is identical (save for the notation errors in the drawing where they tagged the 6P connector as 4P and the 4P connector as 6P)
So we have the same number of spark plugs(4), firing by a 'spark unit' that is shown in both schematics to be the same. Plus I advised he research the resistance load on the ignition coils in the service manuals to make sure those are the same in both the donor and original coils. Same output parameters would imply the same power requirements from the 2 spark units. ... So ya, I think it's a pretty safe conclusion based on the schematics I sourced, and the OP's sketchy description of what is in front of him, the ignition system "spark unit" should interchange.

Lastly, Honda is not stupid, if Honda can use the same simple ignition component in more then one product line they will, why on earth would they make a spark unit model specific?
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5 wire and 6 pin connector are two different things. This is a typical 5 wire reg/rec connector. It would be listed as a 6p connector on a schematic because it has 6 slots.
Data transfer cable Cable Wire Electronic component Networking cables


And why would Honda make a spark unit model specific? I can think of one reason off the top of my head: the spark unit determines the rev limit. And I’d think a 400cc v-twin probably has a different rev limit than a 750cc four….
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Hope he appreciates us doing all his homework lol & why are you worried about a rev limiter, it's doubtful either of these 1980's carbureted machines has one. And btw this is a TCI not a CDI TCI = Transistor Controlled Ignition
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The alternator differences are interesting as is the ability to wire it. Good analysis so far. need to also assess whether the pulse generators are compatible or need to be swapped as well.

The key issue though surely is what the CDI does. Except that it's probably not CDI at all, but ignoring that for a moment, rev limit is critical as is the timing curve. If those are compatible i.e. close enough to not cause major problems, then go ahead and try wiring the replacement in.

A better solution might be a second hand spark control unit or replacement from someone like Electrexworld or Rex's Speed Shop or HPI.be or a new programmable unit from Ignitech.

Trials is right to start with connectability but functionality of the potential replacement is as important.
This is not a fuel injected motorcycle guys, it's old bone technology in a little black box. These engines are designed to run out of carburetor, there is no hi tech computer on board shutting down non-existent fuel injectors. What you see on the wiring diagram is what you get.
... I've given him the pulse generator coil resistance he should be seeing and if he doesn't then the box is not likely compatible for the CBX pulse generator coils and that ends that.
... the spark unit determines the rev limit. ...
That would be a huge fail, rev limiters work by curbing the fuel supply, not by removing the ignition. Thus has it always been. Your plan to remove the spark at maximum revs under WOT would pump raw fuel into your exhaust system, nobody does that or at least not successfully, it would either melt down or explode.

... once you remove the fuel the ignition spark becomes wasted and has no consequence.
That would be a huge fail, rev limiters work by curbing the fuel supply, not by removing the ignition. Thus has it always been..
I’m curious how you think that was accomplished on these carbureted bikes?
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Rev limiter on a carbureted engine works off centrifugal force, usually in the form of a fan and sail, to shut down the throttle via a mechanical linkage, just like on my snow scoot or lawn mower or generator or roto-tiller or snow blower. Depriving it of spark on and off at max revs would make it backfire to say the least, whats your plan for all that extra raw fuel traveling through the engine, hope it evaporates in the atmosphere or burn and explode in the exhaust ? Nobody does it that way, they stop the fuel flow. Once you stop the fuel flow stoping the spark would only serve to foul the plugs rapidly, nobody would do that even on a fuel injected engine, on fuel injection you simply don't activate a fuel injector for a cycle or two and the task is accomplished. Carburetor you rev limit by backing off the throttle, which is shutting down the fuel, it's mechanical.
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I don't have a dog in this fight, and it's been an interesting read, but I do know that plenty of motorcycles have rev limiters built into their CDIs....including carb bikes.
How about this Gents.
Working of the Rev-limiter:

A rev limiter can use following types of methods to control high revs-
Spark control:


When the motorcycle reaches redline the engine closes the spark. This method is not very sustainable as the system keeps injecting the fuel into the cylinder and keeps releasing it without combustion, from the exhaust pipe. This type of control affects much internals of the bike including by the catalytic converter. When the RPM is dropped below the limit, the spark is restored. Usually, in this case, the primary peak voltage required to cause the spark is reduced as a result the ignition does not take place.

Fuel control:

Fuel control regulates the fuel flow into the cylinder and only the air goes in and comes out. Once the engine is at redline, the fuel supply into the cylinder is restricted and a lot of air enters, this causes the air-fuel mixture to become lean which refers to the burning of fuel with an excess of air in the IC engine. Engines used in this process can support higher compression ratios and provide better performance; this also increases the fuel usage and makes the engine more efficient.
In both of these cases, there is a hard-cut and a soft-cut type of rev limiting. Hard cut simply cuts either the spark or fuel completely. This type of system causes the RPM needle to linger between the set RPM point and a little below it because, at the set RPM limit, the fuel or the spark is cut which causes the RPM to lower down, which restores the spark or fuel causing the RPM TO again increase. Soft limiters partially cut the spark or fuel supply before reaching the set RPM, allowing it to climb slowly and then remain at the set limit.
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