DT175MX won't start

[Cynic]

I'll have a think on it, hitting the sack now. Start work at 0230.

[philhill]

I'll have a think on it, hitting the sack now. Start work at 0230.

DT is still stripped down and looking sad waiting to be kicked into life. I am guessing that as we haven't solved the problem yet it is going to get expensive from now on. Is there any way I can test the CDI or is there someone I can take it to to get it tested? Also is it possible to test the output direct from the mag? Phil

ps I am wanting to restore the rear end of my DT to original. Have just won a metal inner m/guard from US ebay for $9 + $32 postage which is about £28 which seems a good price! I now need the plastic rear mudguard in either white or red, does anyone still sell these at reasonable prices? I also have two rear light brackets but they arn't the same, one is longer than the other so not sure which is correct, or if either are? Does anyone have a pic of the correct one for a DT125MX 1982 and rough measurements for the fitting holes? Thanks Phil

[Airhead]

There is only one back light for UK bikes, I suspect German one may be slightly different with mountings for side reflectors possibly. Anyway can you post pictures?

As for mounting holes...there are holes in the metal inner guard, the outer ones line up plus one for a cable entry into a recess in the metal ...dont get the question

lets check the magneto coils, how many wires does your CDI have?

If all else fails it has to be a replacement CDI but thats after we have tried everything and found no faults.So lets get on with the fault finding

[blackhat250]

Hi phill" been thinking, take coil off mounting [ to frame] . clean frame so as coil gets good earth,

I had this problem with a husqvarna , weak intermitent spark, scraped frame clean , and yahoo. fired.

[Airhead]

Hi phill" been thinking, take coil off mounting [ to frame] . clean frame so as coil gets good earth,

I had this problem with a husqvarna , weak intermitent spark, scraped frame clean , and yahoo. fired.

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

[philhill]

Hi, still waiting for the rear mudguard to arrive so don't know which fits. I think the smaller is off a DT100. Hopefully you will see an image below, not done this before

Will have another look at the earthing of the ignition coil but just got back from work and going to have my dinner first. The CDI is 6 lead, 3 in and 3 out. Phil

Off on the Guzzi now for few days holiday, going to leave working on the DT till the weekend, hopefully you can help me solve the problem then. Thanks Phil

[Airhead]

Off on the Guzzi now for few days holiday, going to leave working on the DT till the weekend, hopefully you can help me solve the problem then. Thanks Phil

were off on the squires meet up at weekend Phil, well me and 'Cynic' are

so like I said, it is wise to unbolt the HT coil, clean up the ground lug with the black wires and clean off the stoving / paint at the mounting point, especially the bottom one that the lug is on.

having done that

Disconnect all the 6 wires from the CDI.

The 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, (Magneto charge coil)

White/Red, Meter to 200 Ohms, expect 12.4 Ohms (Magneto pulser 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 behing 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 and if so I can lend you one to prove it until you can source your own from good old ebay

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

[Cynic]

were off on the squires meet up at weekend Phil, well me and 'Cynic' are

Hope we get better weather than the weekend we've just had. 6 large and expensive tents trashed (terminally) by the wind on the campsite we were on, with our caravan . Noah would have had his doubts on the rain too struth.

Then today

[philhill]

were off on the squires meet up at weekend Phil, well me and 'Cynic' are

so like I said, it is wise to unbolt the HT coil, clean up the ground lug with the black wires and clean off the stoving / paint at the mounting point, especially the bottom one that the lug is on.

having done that

Disconnect all the 6 wires from the CDI.

The 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, (Magneto charge coil)

White/Red, Meter to 200 Ohms, expect 12.4 Ohms (Magneto pulser 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 behing 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 and if so I can lend you one to prove it until you can source your own from good old ebay

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

Hope you two had a good time at the Squires Cafe, I have been enjoying the roads around Wales this week and had a great time except for the Guzzi handling like a pig on rollerskates, now sorted and down to worn tyres and fork pinch bolts!

Anyway back to the DT. Have checked the readings and don't get many as they should be! Don't know if this is a good or a bad thing regarding expense in rectifying? Figures are as follows;

Readings between:-

Orange wire and earth = 1.5 [200 Ohms scale]

Brown wire and earth = varying and rising between 6 and 10 ![20k Ohms scale]

White/red wire and earth = 10.3 [200 Ohms scale]

Both black leads the same between earth point on ignition coil at 0.4 [200 Ohms scale]

Black/white and earth

ignition off = 0.5 [200 Ohms scale ]

key on = 0.08 [20k Ohms scale] I also got 0.31 on 2k and 0.9 on 200ohms which I double checked and don't understand?!

With the kill switch down/on/in kill mode I got 1.

I have put figures in bold where the scale is different to your stated ones.

All connections appear good but I haven't pulled of the flywheel to check inside. I can't make any sense of the above but if it is the charge coil wouldn't that just affect battery charging and not ignition? Also am I better getting original or going to Electrex World [?correct name] ?

Hope you can make sense of this? Phil

[Airhead]

OK on fist glance there is an issue with the charge (aka source) coil, this is to charge the ignition capacitor in the CDI not the battery.

Check and double check the connections near the magneto. has the wire come off the plug or socket, any corrosion etc. Unplug it and test from the connection on the mag side and an engine case screw, is it the same?...confirming a coil issue. I cant help thinking this is a connection issue, you dont just 'go on holiday' come back and find your coil went kaput

If it still tests bad, pull off the flywheel and give it a viual inspection for now.

Electrex world will supply you one and your bike will no doubt be up and running cheaply but it will not likely fall within the quoted spec of 420 Ohms, I have one of theirs fitted at the moment and it measures 381 Ohms . A yamaha one will be expensive unless you get lucky on ebay ...which is doubtful. I just bought myself one from the states. All things considered if it were me I would go for the Electrex world one.

Other concern is the black/white, disconnect it at the CDI when testing for spark in the short term until you find the reason for the apparent path to earth.

[philhill]

Hi, still waiting for the rear mudguard to arrive so don't know which fits. I think the smaller is off a DT100. Hopefully you will see an image below, not done this before

Will have another look at the earthing of the ignition coil but just got back from work and going to have my dinner first. The CDI is 6 lead, 3 in and 3 out. Phil

Off on the Guzzi now for few days holiday, going to leave working on the DT till the weekend, hopefully you can help me solve the problem then. Thanks Phil

Hi, haven't made any progress with the sparking but the inner metal rear mudguard has just come and i have offered both light fittings up to it and they both fit !! I was hoping this would identify the correct one but obviously this doesn't help now. I think it must be the larger one with the larger fixing holes but can anyone confirm and tell me what the other one is and i will put it up on ebay. Phil

[philhill]

OK on fist glance there is an issue with the charge (aka source) coil, this is to charge the ignition capacitor in the CDI not the battery.

Check and double check the connections near the magneto. has the wire come off the plug or socket, any corrosion etc. Unplug it and test from the connection on the mag side and an engine case screw, is it the same?...confirming a coil issue. I cant help thinking this is a connection issue, you dont just 'go on holiday' come back and find your coil went kaput

If it still tests bad, pull off the flywheel and give it a viual inspection for now.

Electrex world will supply you one and your bike will no doubt be up and running cheaply but it will not likely fall within the quoted spec of 420 Ohms, I have one of theirs fitted at the moment and it measures 381 Ohms . A yamaha one will be expensive unless you get lucky on ebay ...which is doubtful. I just bought myself one from the states. All things considered if it were me I would go for the Electrex world one.

Other concern is the black/white, disconnect it at the CDI when testing for spark in the short term until you find the reason for the apparent path to earth.

Hi, whats the recommended method for stopping the engine from rotating whilst undoing/doing up the rotor nut, without special tools? I have considered putting a screw driver through the drive chain but dont want to damage the chain! or a spanner on the lock nut on the small sprocket with the engine in gear or a G clamp on the rotor body? any suggestions? Phil

[philhill]

YIPEEEEEEEEEEEE, not sure what i did but after connecting and disconnecting the wire connections near the mag and pulling and untwisting the wires going into the mag I decided to try for a spark and there was a faint blue one each time so put the plug back in and it started about tenth kick, now firing up first kick each time. Must have been that dodgy connection!!! Smoking loads for some reason but I'm happy, just going to put the seat back on and give it a short test ride, hopefully all will be well. Thanks for help. Phil

[philhill]

YIPEEEEEEEEEEEE, not sure what i did but after connecting and disconnecting the wire connections near the mag and pulling and untwisting the wires going into the mag I decided to try for a spark and there was a faint blue one each time so put the plug back in and it started about tenth kick, now firing up first kick each time. Must have been that dodgy connection!!! Smoking loads for some reason but I'm happy, just going to put the seat back on and give it a short test ride, hopefully all will be well. Thanks for help. Phil

Yep, is now running well, smoking was down to all the kicking over and the oil pump still pumping oil into the barrel and not getting burned. Still have problems when the CDI is fully connected to the loom and cuts out/won't start. Key Switch is not original but cheap looking ebay item, could this be an issue here?

Also do you know which is the correct light bracket if any? Phil

[Airhead]

Good well done, issues with sudden ignition failure, ie 'going on holiday then it wont work' are well worth investigating without lashing out on an expensive CDI. Having said that I do think it is wise to watch out for a CDI at the right price now you have the bike running. Smoke...aw dont worry about that...the more the better

Hi, whats the recommended method for stopping the engine from rotating whilst undoing/doing up the rotor nut, without special tools? I have considered putting a screw driver through the drive chain but dont want to damage the chain! or a spanner on the lock nut on the small sprocket with the engine in gear or a G clamp on the rotor body? any suggestions? Phil

I use this Phil, its a chain wrench for removing car oil filters

in action I cut some strips of fabric backed rubber from some work gloves and place these under the chain for a good grip. Same method for tightening only I then use a torque wrench on the nut.

As for the light brackets you never really gave us any useful info like measurements or better pictures

[Airhead]

Here you are Phil

[blackhat250]

what happened to phill " last seen 13thsept,,