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DT175 Basic Wiring


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Hey all, just trying to get an old 1980 DT175 to start up. No spark, but checked resistance through stator/magneto windings and seem good enough to produce. Coils seems shot but just ordered a new once. I just wanted to check if my wiring is correct before I replace the CDI or other components. My CDI has 7 wires, with all connected except for one black wire cut extremely short. Any ideas? I only care about getting spark, and am not running a battery, hence the battery being omitted and all wiring past the voltage reg listed as "To accesories." Link to an image of my diagram below. Thanks! 

https://i.ibb.co/1v46why/IMG-4649.jpg

 

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Hi Blake and welcome, is this any help?

 

DT175MX Ignition checks

There were two versions of ignition systems on DT175MX bikes. The mk1 version from the earlier bike had a 7 wire CDI the early bikes had a round section swing arm.

The mk2 version had a 6 wire CDI, the red wire is absent on these. These bikes have a square section swing arm.

 

The HT cap (AKA spark plug cap)

unscrew it off the HT lead, it is supposed to be a resistor cap so should be around 5K Ohms
The ignition coil primary...Orange wire to battery neg should be 1 Ohm +- 10%
The ignition coil secondary...HT lead to battery neg should be 5900 Ohms +- 20%

If the readings are much higher, check the ignition coil has a clean ground connection.

Yes and the ignition coil mounting is a wiring harness ground point too, so check its clean and bright there.

 

Disconnect all the wires from the CDI.
Then using your multimeter on the loom side of the connectors.

Black probe on a clean part of HT coil ground point
Red probe on......



Orange, Meter to 200 Ohms, expect 1 Ohm (HT coil primary)

Brown, Meter to 2k Ohms, expect 420 Ohms for  mk1 and 300 Ohms for mk2 (Magneto charge coil)

White/Red, Meter to 200 Ohms, expect 12.4 Ohms for mk1 and 10 Ohms for mk2 (Magneto pulser coil)

 

Red, Meter to 200 Ohms, expect 13.6 Ohms for  mk1 only. (Source coil 2 or high speed coil)

Black female connector, Meter to 200 Ohms, expect dead short
repeat for black male connector
Any difference in the results for the two black wires may possibly be rectified by cleaning the front engine mounting bolt and a little of the frame behind the bolt head, then tighten to torque spec.

Black/White, Meter to 20K Ohms, with ignition off expect dead short, with key on expect open circuit, with kill operated expect dead short (Engine kill operation)

 


If all these tests are good you would be well advised to try another CDI.

If they are not good...reading higher...disconnect and clean any plugs/sockets you find along the way, if the magneto coils are reading lower, new ones needed if more than 10%...or so the book says
file:///C:\Users\Dell\AppData\Local\Temp\msohtmlclip1\01\clip_image001.gif

 

Finally, if you are working with a box full of mixed parts!

Mk1 1 flywheel is Mitsubishi F3T250, it has two slots in the face of the flywheel

 

Mk2 flywheel is Mitsubishi F3T251, it has four slots in the face of the flywheel

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33 minutes ago, Airhead said:

Hi Blake and welcome, is this any help?

 

DT175MX Ignition checks

There were two versions of ignition systems on DT175MX bikes. The mk1 version from the earlier bike had a 7 wire CDI the early bikes had a round section swing arm.

The mk2 version had a 6 wire CDI, the red wire is absent on these. These bikes have a square section swing arm.

 

The HT cap (AKA spark plug cap)

unscrew it off the HT lead, it is supposed to be a resistor cap so should be around 5K Ohms
The ignition coil primary...Orange wire to battery neg should be 1 Ohm +- 10%
The ignition coil secondary...HT lead to battery neg should be 5900 Ohms +- 20%

If the readings are much higher, check the ignition coil has a clean ground connection.

Yes and the ignition coil mounting is a wiring harness ground point too, so check its clean and bright there.

 

Disconnect all the wires from the CDI.
Then using your multimeter on the loom side of the connectors.

Black probe on a clean part of HT coil ground point
Red probe on......



Orange, Meter to 200 Ohms, expect 1 Ohm (HT coil primary)

Brown, Meter to 2k Ohms, expect 420 Ohms for  mk1 and 300 Ohms for mk2 (Magneto charge coil)

White/Red, Meter to 200 Ohms, expect 12.4 Ohms for mk1 and 10 Ohms for mk2 (Magneto pulser coil)

 

Red, Meter to 200 Ohms, expect 13.6 Ohms for  mk1 only. (Source coil 2 or high speed coil)

Black female connector, Meter to 200 Ohms, expect dead short
repeat for black male connector
Any difference in the results for the two black wires may possibly be rectified by cleaning the front engine mounting bolt and a little of the frame behind the bolt head, then tighten to torque spec.

Black/White, Meter to 20K Ohms, with ignition off expect dead short, with key on expect open circuit, with kill operated expect dead short (Engine kill operation)

 


If all these tests are good you would be well advised to try another CDI.

If they are not good...reading higher...disconnect and clean any plugs/sockets you find along the way, if the magneto coils are reading lower, new ones needed if more than 10%...or so the book says
file:///C:\Users\Dell\AppData\Local\Temp\msohtmlclip1\01\clip_image001.gif

 

Finally, if you are working with a box full of mixed parts!

Mk1 1 flywheel is Mitsubishi F3T250, it has two slots in the face of the flywheel

 

Mk2 flywheel is Mitsubishi F3T251, it has four slots in the face of the flywheel

Yes, I have read this walkthrough. My bike appears to be a MK1, so the 7 wire CDI is appropriate. I am mostly just wondering if my wiring is correct. I cant seem to find a wiring diagram to this bike that has the CDI pictured. 

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Hi Blake

I own a 1978 MX with 7 wire cdi, there is a wiring diagram available in the Haynes owners workshop manual .Yamaha 100,125 &175 trail bikes. Brown cover Book 210. On page 167.

 

hope that helps.

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20 hours ago, Airhead said:

there should be a red wire connecting stator and cdi.

 

whats the question mark mean?

There is no red wire out of the stator. Red/white, brown, black, yellow, and green/white come out of the stator. Question mark is a black wire coming out of the cdi cut very short not connected to anything. 

23 hours ago, NE0 said:

Hi Blake

I own a 1978 MX with 7 wire cdi, there is a wiring diagram available in the Haynes owners workshop manual .Yamaha 100,125 &175 trail bikes. Brown cover Book 210. On page 167.

 

hope that helps.

Ill take a look

Edited by blakemcelroy2000
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