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Makotosun

[Help] with my '73 DT3 250, having ignition issues

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If you have timed the bike correctly with a dial indicator, then replace the condensor on the stator. I have seen these be weak enough to show a spark kicking the bike over, but will be hard starting or erratic running.
27 Jan 2023 01:29 #51

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Umm, i learn every day. Thanks to MarkT.
27 Jan 2023 18:32 #52

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Run 6volt battery ignition if all else fails. Two wire diamond 6volt coil if they still make them. Cut the source coil wire off at condenser. Then nothing much else to do. Black wire to ya new 6volt coil & battery to other coil wire. Then keep battery charged using the lighting 'yellow wire' through the rectifier. Simple setup. Might even get enough out of the yellow to keep a small 12volt charged at revs & using a 12volt coil of course. Ignition wouldn't draw much. Ok, shutup 'me'.
27 Jan 2023 18:42 #53

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  • 19stuberd
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Hey everybody! Interesting and potentially groundbreaking news for everyone.
So I took the bike back to the lab with the oscilloscope and got some real readings this time, both with points covered and uncovered. Everything seemed to be in the right approximate voltage range and everything, even on kick. One thing that I noticed, however, is that every time I've made spark I've been doing one thing: I have been cranking the flywheel in reverse. Even at the lowest speeds I now have a nice hot spark when I'm cranking in reverse with a drill, but it occurred to me that the kickstarter spins the engine in the opposite direction and that's the way that the engine actually runs. I thought that maybe the voltage on kick was just too low compared to anything the drill could produce, but the readings show that the voltage on kick is just as high as the voltage from spinning in reverse with the drill. I tried spinning it in the normal direction (hard to do without loosening the nut) and sure enough even at the highest speeds I have no spark.

So my question is what could cause the spark to work in one direction but not the other? I feel like it's probably something obvious. Hope to hear from you all soon!
29 Jan 2023 11:34 #54

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  • 19stuberd
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Oh also this is just me forgetting what a condenser is called lol. Sorry I just learned how all of this stuff works when mine started breaking so the terminology is new to me. Bike still uses points, I was in fact referring to the condenser.
29 Jan 2023 11:36 #55

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As I tried to explain earlier, the EMF of the moving magnets need to create a voltage peak at or very near the moment the points crack open.

As simple as these systems are, there is a lot of engineering and maybe a little "magic" that makes them work.

And as I've said before, it's kind of rare for a source coil to be bad unless it's shorted or open... ohm reading just needs to be in the ballpark. I have one bike with a pretty crunched coil and it sparks great. Usually it's dirt points... sometimes a bad condensor (which technically IS a capacitor... so you weren't wrong calling it that)

Anyway, the only thing that comes to mind is a question... is it possible you re-would the coil in the opposite direction from the way it was wound originally? All the details of how the wire is wrapped around the core make a difference in polarity, etc.

That might not be the answer... but I know the direction and the way the coil is wrapped is important to the way voltage is generated when each pole of the magnet passes by. And then there the "timing" of the voltage peak NEEDING to coincide with the moment the points open.... if coil is wound differently it would still make voltage but timing of when the peaks occur could be different...
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
29 Jan 2023 12:11 #56

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I'd say MarkT nailed it--or you nailed it yourself--sort of--by giving the clue of reverse spinning works good. Now its getting interesting!!. Can you flip the coil end for end or does it have a step sitting over the mount. If that can't be done can you swap ends to solder to condenser & to earth--[not sure if that ends up the same as flipping it over]. Had a TT250 at work where we got the coil rewound & same issue so rewinder said swap earth & other wire which was easy as both headed up the loom by memory so just swap the brown & black in my case. Talking cdi stator coil but same principle.

One more important thing when this is sorted. Be VERY sure the flywheel nut is TIGHT. If it'll unscrew spinning it with a normal drill [not hammer drill] then it's not tight enough by a long shot. Hopefully we'll hear it runs soon. Best of luck.
Last edit: 29 Jan 2023 13:36 by RT325.
29 Jan 2023 13:29 #57

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  • Ht1kid
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MarkT do you think he adjusted the points after TDC. How did you set your timing what was your procedure please tell us details or did I read it wrong  19stubard are you getting spark spinning it clockwise or counter clockwise 
Last edit: 29 Jan 2023 14:32 by Ht1kid.
29 Jan 2023 13:32 #58

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  • 19stuberd
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VERY interesting! I'd say that it's a real possibility that the coil was rewound "backwards." I will try resoldering the leads the other way and see if that does anything, if not I may try rewinding the damn thing as it doesn't seem like it would be able to just be flipped over (coil has flanges on the top).

Also with respect to the timing-- I am pretty sure that I set it BEFORE top dead center. I positioned it at TDC and then rotated it CLOCKWISE until it was at 2.8mm. To clarify as well, bike has quite good spark spinning CLOCKWISE and zero spark at all speeds spinning CCW.

Also I will make sure that before I finish this up I will give it a good proper torquing on there. Will update, any other thoughts appreciated, thanks again for everything!
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29 Jan 2023 17:07 #59

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Timing is correct I sure hope reversing your wires works for you. Fingers crossed 
29 Jan 2023 17:33 #60

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