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1975 DT175 Misfire

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Replied by MarkT on topic 1975 DT175 Misfire

Thinking about it...  diode might be on main harness side on connector and not stator side.  Should be a plastic plug if I remember correctly.  Diode is near the plug and it's like a solid stiff section rather than a bendy wire like rest of wires.  It's been too many years since I worked on my twin shock Dt175...  and it's not accessible at the moment so I can't go look at it. 

Anyway, try bypassing diode. 
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
01 Aug 2022 21:53 #21

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Replied by RT325 on topic 1975 DT175 Misfire

Ok, seeing as it won't now start. Try plug out & spin it with a reverse drill on the crank as fast as you like & go looking in the flywheel & around. Is the plug coil earthed well. Mount screws would need to be loose seeing it was running ok--then it wasn't. This is turning into an interesting one for sure. I'll put the headphones on for video listen again.
Last edit: 01 Aug 2022 23:45 by RT325.
01 Aug 2022 23:23 #22

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Replied by RT325 on topic 1975 DT175 Misfire

I could suggest dropping the complete exhaust for a quick try, but i won't say that as don't believe it. But i said it if it is that lol. Ok thinking outside the square--has it cracked a magnet in the flywheel, cracked across. I saw a similar thing at work where the magnets were removable & the owner had been playing. & he'd put one in back to front which upset what magnets do push pull whatever & the foreman spent some time sorting it but 'he got it' & was a happy camper!!. Not sure i would've ever worked it out but sure was one to never forget.
01 Aug 2022 23:44 #23

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Replied by kwzl1 on topic 1975 DT175 Misfire

Thanks for all the suggestions. During my rebuild I replaced all three stator coils and the wiring harness including the diode with NOS items, so the diode "should" be good, but it will easy to bypass it and test it out.
Also, thanks for the link to the info on relocating the condenser. I will probably do that as well.
02 Aug 2022 09:27 #24

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Replied by kwzl1 on topic 1975 DT175 Misfire

I will try bypassing the diode. Thanks,
02 Aug 2022 09:28 #25

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Replied by kwzl1 on topic 1975 DT175 Misfire

Thanks for the reply. So many possible causes. I will have to keep checking and trying different things until I can find the problem.
02 Aug 2022 09:31 #26

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Replied by nutman on topic 1975 DT175 Misfire

Hi, looks very much like my journey with my dt175c. I tried everything and suspected everything. Took me weeks, and tried most things other members suggested.
Turned out, spark plugs can foul incredibly fast and will throw you off track with diagnosis. And I've never worked on a two stroke that is so sensitive as this one.
Have your timing a little bit off and you would swear you have blown the crank seal. Or it will produce a tiny intermitting spark.
In the end I will always use a timing strobe and by now I know the sweet spot for the spark.
I also isolated the points with an bypass wire for diagnosis, just to check the stability of the points and the resistance. Good looking points can still go all over the place with their resistance. Too much wobble in the advancer cam is also not helping.
Persevere, you will become a happy rider at some stage.
The following user(s) Liked this Post: RT325, Sneezles61
04 Aug 2022 07:34 #27

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