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Technical Motorbike Help

Yamaha DT175 lgnition

Yamaha  DT175 lgnition - Forums [Biker Match] Yamaha  DT175 lgnition - Forums [Biker Match]
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Yamaha DT175 lgnition

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I have an ignition problem that is proving difficult to overcome. After a comprehensive rebuild the bike ran reasonably well for around 110 miles but then the ignition source coil failed. I had a company rewind all three coils and fit new points and condenser to the stator plate (very expensive I thought at £225) There is continuity through the points when open which confused me..the company assured me this is correct and dismissed any further comment. Not at all helpful.
I have replace the condenser as the soldered connections looked amateurish and by using an aftermarket device deduced a change in resistance when the points open..but I'm still not getting a spark. In desperation I've wired my the magneto discharge directly to the HT coil to eliminate any wiring loom failure..and tried setting the points at various degrees..but still no spark...
Matt: I've not revealed the name of the rewind company as I m not sure of any protocol..but would like to as it may invite comment to contrary to my experience..thanks for reading and any ideas will be gratefully received..

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Deleted Member @ 22/05/2020 12:20  

The ignition system on these bikes is extremely simple. The Black wire from the magneto runs to the coil. The kill switch and ignition switch simply pull this circuit to ground to "kill" spark. First thing I'd do is disconnect the ignition switch and kill switch and see if that solves your problem. If not, with those still disconnected measure continuity on the black wire from the coil to the points. If you have continuity, measure resistance between the black wire and ground while slowly rotating the flywheel so the points open and close. With the points open the resistance should be a few ohms, with the points closed the resistance should be less than 1 ohm (a few tenths of an ohm). If the resistance with the points open is less than an ohm either your points are not opening or you have a short to ground in the black wire

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Deleted Member @ 22/05/2020 17:45  

Cheers Paul, I have wired the points discharge cable, the black wire, directly to the HT coil so, although the kill switch failing is a good point, I have eliminated it ...just having your response will inspire me to have yet another look at analysing the fault. I'll measure the resistance as you suggest and keep you posted. Hopefully with a short clip of it firing up..😂..thanks again.

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Deleted Member @ 23/05/2020 00:18  

I hate wireing 😂 and modern bikes scare me with all the gubbins that can go wrong, old bikes were made simple and to the point, by old benly was designed to be fixed by the side of the road wearing a pair of oven gloves 😂

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Deleted Member @ 23/05/2020 13:57  

Paul that's made me KLR has so many relays and cut out switches it borders on the rediculous...I've taken in board your comments..and still no desperation I've installed a condenser from a suzuki..and it fired up this afternoon..first time since the source coil failed 9 months ago..I ran it up and down the drive then stopped it to put some pressure in the tyres and wont start ! Having a brew and contemplate...

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Deleted Member @ 24/05/2020 14:41  

I can't be sure but I think there's a diode that runs from the black wire on the condenser these can sometimes burn out or try a proper yam condensor, at least you now know it runs lol

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Deleted Member @ 24/05/2020 19:13  

Thanks Paul, the diode you talk about, is that in the loom somewhere? As I cant find one in the circuit anywhere....would you have any idea where I could get guidance on the advance mechanism given the machine is running it's original wiring loom which is serviceable but not first class condition ...An element you might be able to advise on is the mechanical advance system. The cam apears to have a degree of free play(I just noticed this for the first time ) and I'm sure there should be a bob weight attached to the pivoted mechanism but I cannot find any information not even any images of the set up. The situation now is; l gave a big fat spark, a wet plug and it wont start, so I'm wondering if the timing cam, given the free play I mentioned may have moved..thanks

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Deleted Member @ 25/05/2020 05:35  

Hi Paul and anyone else watching this conversation..The fault has been rectified. It's now running with a suzuki gt185 condenser and a Triumph odd combination but the original coil only gave a weak spark as did the brand new chinese item the 1960s Lucas coil gives a much stronger for the condenser, original dt items are difficult to find so on recommendation I fitted the suzuki unit. I hope this has been of help to any individual rebuilding an old 70s two stroke. All I need now, is a destination !

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Deleted Member @ 02/06/2020 23:06  

I have a 1972 DT250, I had a lot of problems with the ignition system, it's now running a 12v system with electronic ignition.
Before it was converted, it used to kick back on the kick start and nearly break my ankle. I would highly recommend it.

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SteamBiker @ 14/08/2020 17:45  

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