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Makotosun

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

  • RT325
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I'm should go read before offering ideas but--i guess ya spinning it anti clock sitting looking at it. Soldering you mentioned, but if its contacting then i won't go there. I wonder if its just plain 'not' producing enough voltage at start speed.

So here's an idea to prove a point. Find the lowest voltage lighting coil wire & bridge it to the black up top as it goes to the plug coil, so it feeds back down to the condenser & points. Snip the source coil wire at the condenser seeing you need to try soldering again so no harm done. So then you'll have likely too much voltage but should spark good. I had a little 100cc running that way but was hard on the points & found lowest output lighting was best--or less hard on the points. So only for a testing try if you want too. Points set to 15 thou max. Flywheel tight or key will be damaged or will break. Hope for some good news.
20 Jan 2023 22:57 #11

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300 RPM would be 5 revs per second. 

In video you can hear each "thwup" as piston passes through TDC...  when you're spinning it slow, guessing you're at 100 RPM or less from the frequency of the noise pulse.  Just might not be spinning fast enough. 
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
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21 Jan 2023 07:07 #12

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  • RT325
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Too be honest i recon my points mags would spark at the plug if i just spin it around by hand on the flywheel--i've done it before, but long ago. They're a pretty good system when in good condition. I think you said you unwound the coil & rewound it. I'll go back & read--Ok read most of it quickly. CDI capacitor i'll take as condenser so ok--total rewind of coil, is there a possible clue there but reads like you did well--very well. Is it protected from the pole its wound onto--i'm no experts but think the have a wrap around stuff to isolate incase the coating gets off & shorts to earth, i guess you have that under control. So no short to earth or the coil pole. 0.5 ohms sounds slightly low. Ok i have my factory folder of yamaha stuff & says 0.508 ohm so ya ok then & as you say. lighting out of curiosity says green/red 0.061 green 0.206 yellow 0.292 white 0.167. So what i spouted about using lighting coil on a 100cc was probably totally different in resistance--but anyway. So i'm no help am i haha.
21 Jan 2023 13:42 #13

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just nosing through my resistance pages i see an lt2 100cc has 2.1 on the source coil & lighting varies from .58 to .60, but smaller flywheel & magnets etc so i don't know. Maybe "maybe" a little more resistance from your source might give better start voltage. I don't really know what i'm talking about but do a lot of guessing. Go buy an "89 DT250F complete CDI system with flywheel & your worries will be over.
21 Jan 2023 13:53 #14

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You can get a spark by giving it a quick twist with your hand if you do it at the right spot.  But who knows what RPM that would be? 

Easiest test in the world is to just give it a few kicks with the kicker and I'm guessing if plug shell stays grounded you'll get a nice spark. 

Or you can worry about it and try to fix something that might not even be broken.

My guess is the original stator coil probably was fine...  it's not that common for them to go bad unless physically damaged...  for example by someone using a jaw puller...  and when they do they are usually completely open or shorted. 

 
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
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21 Jan 2023 14:00 #15

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  • 19stuberd
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Hey everyone! I'm back to work on the bike and I've noted what you have all said. I am working on the stator, trying to understand the wiring, but it's difficult because there are numerous wires that seem to just go into the coils for no reason and seeing what connects where is difficult i.e. I can't tell if these wires are simply being wrapped over by the windings or if they tap into the windings at some point. Continuity testing is also fruitless because normally I'd check that to see what connects where but pretty much everything is returning a positive result because I think the differences in resistance are so small that my multimeter (.1 ohm precision) can't detect it. I also don't know which coil has the lower output or how I would find that out, as in whether I need to determine that experimentally or if it's a known thing. Any diagrams besides the ones in the manual would be greatly appreciated. I'm beginning to gain a little bit of hope! Thanks a million times for all the help.

P.S. That soldering job was done by the shop, if I had done that myself I don't think I could have brought myself to post it on here.
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21 Jan 2023 14:02 #16

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  • 19stuberd
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Also just realized that even MORE comments have popped up since I last read this post this morning (you guys are the BEST!) but so to answer a couple things, I had thought about re-rewinding the source coil with a few dozen more windings to increase its voltage output (I've taken a few electrical engineering courses as a part of my degree and from what I know in any coil the number of windings directly correlates to voltage output whereas conductor diameter relates to amperage), as a matter of fact I could even use the core off of my spare stator so as to keep the one I rewound to spec in usable shape. Also this business with buying a '89 DT250F stator, is this true? Because if so I would absolutely consider doing it, as I've said I'd do anything to get this bike running at this point. Also are you saying the lighting coil mod might not work? Also also if it is still viable, which wire from the coil are you saying to connect to the black wire? Thanks again for all of the replies, it really does mean the world to me.
21 Jan 2023 14:13 #17

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I'm happy you mentioned the shop did the soldering. I won't feel bad about mentioning it now lol. Just be sure it's not touching the condenser body. Needs re-melting properly, but!! Is the original stator still in one piece--go back & try that.
21 Jan 2023 14:13 #18

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All those cdi systems, statpr & flywheel will bolt straight straight on from first model of DT350A in "74 right through to DT250/400 & "79 [correct me someone if wrong]. But it wasn't until later "70's that the stator trigger coil improved on 250 & 400, hence i said "78 but maybe "78 or whenever they changed. Look on Partzilla for the year change as trigger goes from a big horrible thing to a tidy trigger. Anyway, another option of course is any DT250 points mag up until the cdi change as 250's stayed points until quite late. If you find a later DT250 points mag you need the flywheel too as they belong together. Ok, i'm out of here for the day--day in NZ. Hope i've not messed you around & best of luck.
21 Jan 2023 14:26 #19

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  • 19stuberd
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Also one final question relating to the points, I tried to post this already but I don't think it worked. I don't really know how to check the point gap, allow me to explain. This will be a bit wordy but I want to explain clearly. As I understand it, points are essentially a switch that are held closed under spring tension and free to be opened an arbitrary distance manually i.e. with your fingers. In the bike, however, the points are opened by a raised portion on either the magneto or shaft which acts as a cam, opening the points to a fixed distance before allowing them to close again under spring tension. This distance can be adjusted by moving the fixed position of the points so that the cam either pushes them more or less open. The issue with this is that firstly I don't know what surface actually actuates the points on the bike, which I need to know for adjusting purposes. This plus another issue of the flywheel covering the points during operation means that I can't see what's opening the points and I can't see how far they're opening. I hope this explains the issue clearly and that someone can help me with this, as the manual was no help.

Also to Mr. 350, are you saying that I should not do the coil mod? If you think I should still do it, which coil is the less output one and which wire should I connect to the black one?

Thanks again for everybody's help, it really does mean the world to me.
21 Jan 2023 16:05 #20

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