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1974 DT250 Voltage Conversion

  • JWormy
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1974 DT250 Voltage Conversion was created by JWormy

Hi folks, 

I've recently acquired a 74' DT250 that someone had tried to convert to a cafe racer and gave up, and a 75' that is mostly original to use for parts (Carb, reed valve, oil tank etc). Ultimately, I would like to take the '74 and convert it back to it's former off-road glory and ditch the cafe look. Not my style. Anyway, I've been reading the previous posts related to converting these bikes to 12V (thanks to those that came before me, documenting your experience has been extremely helpful), and I'm starting to believe that the previous owner of this bike had already starting converting to a 12V system. When I received it, the battery had been removed, the wiring harness had been ripped to shreds, and there were aftermarket lights installed. Now, it's possible that he bought 12V lights not realizing that a 6-Volt system wouldn't support them, OR he was indeed attempting to convert the charging/ignition system. So my question to you all is, what is the visible difference between the original 6V alternator and a 12V one? If you can't tell with the naked eye, is there a test I can run with a multimeter? Thanks! 

Hi folks, 

I've recently acquired a 74' DT250 that someone had tried to convert to a cafe racer and gave up, and a 75' that is mostly original to use for parts (Carb, reed valve, oil tank etc). Ultimately, I would like to take the '74 and convert it back to it's former off-road glory and ditch the cafe look. Not my style. Anyway, I've been reading the previous posts related to converting these bikes to 12V (thanks to those that came before me, documenting your experience has been extremely helpful), and I'm starting to believe that the previous owner of this bike had already starting converting to a 12V system. When I received it, the battery had been removed, the wiring harness had been ripped to shreds, and there were aftermarket lights installed. Now, it's possible that he bought 12V lights not realizing that a 6-Volt system wouldn't support them, OR he was indeed attempting to convert the charging/ignition system. So my question to you all is, what is the visible difference between the original 6V alternator and a 12V one? If you can't tell with the naked eye, is there a test I can run with a multimeter? Thanks! 

15 Apr 2022 11:31 #1

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Replied by Gr8uncleal on topic 1974 DT250 Voltage Conversion

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 from Salisbury, UK.

I'm happy to be corrected here, but all of the 12v conversions that I've read about also converted the ignition to cdi. So, take the points cover off and have a peek to see if the old flywheel is present, with the points behind it - if yes, then I would say still 6v system.
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15 Apr 2022 11:51 #2

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Replied by RT325 on topic 1974 DT250 Voltage Conversion

Can you convert a 6 volt to 12 by simply [or not simply] unearthing the lighting coil & running both ends of it to a regulator rectifier then 12 battery. I dunno, thought i read that years ago.
15 Apr 2022 19:16 #3

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Replied by JWormy on topic 1974 DT250 Voltage Conversion

  Alright, finally back to my project. Looks like the original flywheel and points are still present. Which is a bit of a bummer, because now I need to decide whether I want to convert, or spend the time searching for 6V lighting that will be compatible. Anyone have opinions on which is easier? Or a resource where I could order parts for either? I’m also looking for. Compatible flywheel puller. Does anyone have one they like that they could link me to to order one? The flywheel is rubbing in some spots so I need to pull it off, clean it, and inspect the points to see if they’re worth keeping. Thanks again!

Jess
30 Apr 2022 12:40 #4

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Replied by RT325 on topic 1974 DT250 Voltage Conversion

Hope the crank isn't out of 'true' causing rubbing. How's it look spinning it just eyeballing the flywheel circumference. Watching the crank nut doesn't always work as people belt hell out of it trying tricks to get the flywheel off. So thread could be bent fractionaly but taper & flywheel still run true. Bundle of joy aren't i lol.
30 Apr 2022 16:11 #5

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Replied by Gr8uncleal on topic 1974 DT250 Voltage Conversion

Just a fyi, but that flywheel magneto assembly will likely fetch a pretty penny should you decide to go the 12v conversion route. They are popular with DT360A owners whose cdi has gone fubar.
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30 Apr 2022 23:50 #6

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Replied by MarkT on topic 1974 DT250 Voltage Conversion

We don't know your exact situation with the lights...  but is there any reason you simply can't install 6v bulbs?

I bought an original Yamaha turn signal from Yamaha a few years ago for a later 6v bike and it came with a 12v bulb installed.  Simple bulb swap was all that was required. 
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 May 2022 01:10 #7

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Replied by JWormy on topic 1974 DT250 Voltage Conversion

The flywheel seems okay. It's definitely been removed before but doesn't seem warped or damaged. Looks to me that the rubbing is happening on the inside. I'm able to spin it freely by hand, just a little stiff in this one spot. Probably just a lot of grease and grime built up in there. This bike came from Florida and was EXTREMELY greasy and rusty when I got it. Salty air has not been kind to this one. 
02 May 2022 12:57 #8

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Replied by JWormy on topic 1974 DT250 Voltage Conversion

Yeah I could definitely get 6V bulbs, I was just scoping out the option of conversion since I have to replace the battery and most of the wiring harness anyway. Seems like it'll cost me quite a bit to convert to 12V, and since this project is intended to be sold, I will stick with 6V!
02 May 2022 12:59 #9

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Replied by JWormy on topic 1974 DT250 Voltage Conversion

I think I figured out what's causing the "rubbing" on the flywheel. Seems like maybe some mud or a rock got in between the coil and flywheel and smushed it, (for lack of a better term). Also seems like I'm not the first one to crack this open as those solder points don't look like they came from the factory that way... Any thoughts on the impact to charging/spark in this condition?
26 May 2022 16:42 #10

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