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Re:Re:Re:Re:Re:1977 DT400 CDI Box question

  • Thebassguitarist
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1977 DT400 CDI Box question was created by Thebassguitarist

With many headaches of my bike not running right I realized I overlooked a major aspect. Timing. Upon strobing my running motor at idle the strobe is all over the place. It's incredibly inconsistent and never lines up with the timing marks.

I remember reading something a while ago that this failure can be blamed on the CDI box? Am I right in that diagnosis?

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19 Feb 2021 11:42 #1

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Replied by MarkT on topic 1977 DT400 CDI Box question

It's possible it's the CDI box...  but often it seems to be the stator. 

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One thing to try is to take apart and clean all the wiring connections and grounds.  More than one "inconsistent" CDI problem has been fixed by cleaning up connections and grounds.
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
19 Feb 2021 13:36 #2

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Replied by Thebassguitarist on topic Re:1977 DT400 CDI Box question

Will do.

If that doesn't work is there a good way to diagnose between the stator and the CDI box?

Thank you for all of your help Mark.

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19 Feb 2021 13:57 #3

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Replied by MarkT on topic Re:1977 DT400 CDI Box question

There are some cursory checks that can be done with an ohmmeter...  Service Manual in Tech Library details them.

Unfortunately I've had component test perfectly with a meter but CDI doesn't work right...  Yamaha's answer was "replace with known good" which was easy for the dealer to do when these bikes were new and parts were on the shelf or maybe another bike was available to swap parts with...  Not so easy today.

 
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
19 Feb 2021 14:54 #4

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Replied by Thebassguitarist on topic Re:Re:1977 DT400 CDI Box question

Hopefully a friend with a known running dt250 will be kind enough to let me borrow some parts.

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19 Feb 2021 15:36 #5

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Replied by MarkT on topic Re:Re:1977 DT400 CDI Box question

DT250 would have had points unless friend has a 1979. 
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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19 Feb 2021 16:14 #6

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Replied by Thebassguitarist on topic Re:Re:Re:1977 DT400 CDI Box question

It's a 77. I was under the impression they were the same as the 400. Bummer.

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19 Feb 2021 16:16 #7

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Replied by Schu on topic Re:Re:Re:1977 DT400 CDI Box question

Hold that thought........
When you get tired of messing with your CDI issues you may once again be looking for 250 parts. I swapped away from CDIs on my 360 and my 400. I've been happy with it ever since. They start easier and run better now than they did with the CDIs.
Schu

CT175B, CT175C, JT1' JT2' DT360A, GT80B, DT100B, DT125B,
DT175B, DT175C, DT250B, DT400B, Z50, SCR950

Someday, you'll own some Yamahas
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19 Feb 2021 16:32 #8

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Replied by Thebassguitarist on topic Re:Re:Re:1977 DT400 CDI Box question

Tested my charge coil. Service manual says it should read at .33 (I assume ohms) plus or minus 10% and I'm reading 154 ohms. So bad coil then?

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19 Feb 2021 16:40 #9

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Replied by Thebassguitarist on topic Re:Re:Re:1977 DT400 CDI Box question

Just read on another thread that the dt400 is supposed to be 120ohms plus or minus 10%

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19 Feb 2021 16:50 #10

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