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

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

I didn't realize the 77 manual was so vague. 

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I will try to measure mine tomorrow. 

The thing is I've seen CDI's that run great with stator "ohm readings" out of spec and others with ohm readings perfect that don't run at all. 
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 19:03 #11

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

Thanks. I'm going to try another CDI box first off of a running bike, that's cheaper. Then I'll move on to a coil if that doesn't work.

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19 Feb 2021 19:21 #12

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

Thebassguitarist wrote: 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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Unfortunately, Yamaha specs have a lot of errors. 

I looked through my documentation and found the correct specs for the CDI stator coils are:

Source coil: 1.6 ohms +/-10% @68degF
Coil: 166 ohms +/10% @68degF

(The charge coil spec at 0.33 ohms is for the BATTERY charge coil on the stator, not the CDI coil on the stator)

Sounds like you're good.

 
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
20 Feb 2021 07:55 #13

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

Mark,
If the problem I am having is a coil issue should I be focusing on the pulsar coil rather than the source coil? Since the problem I am having is an inconsistent spark issue rather than a lack of spark? Pardon the many questions, I have a lot to learn and am very grateful for all of your knowledge.
21 Feb 2021 12:08 #14

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

The original CDI's are great when they work right.  When they don't...  there just isn't any source for reasonably priced repair parts that can be known to be good.

And there's really no way to test much without swapping parts with known good ones. 

If all connections and grounds are good, CDI box...  if you can get one that's known to be good...  is probably the most likely source of the issue.  Second most likely in my opinion would be stator pulser coil...  third would be source coil... 

In terms of what I'd do?  I'd probably swap to points from a 250 which is what I'm about to do on my DT400.  Or get a VAPE kit. 

Some have had success with the Rex kits...  others have had bad experiences.  Unfortunately the ones with bad experiences don't seem to get much help from Rex to fix the problem.



 
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
21 Feb 2021 12:42 #15

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

Do you by chance have a resistance reading for a known good pulsar coil?

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23 Feb 2021 19:09 #16

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

I can't believe how screwed up some of the Yamaha Literature is!!

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I found a Service Data Sheet that clearly shows the correct specs

Pulsar = white/red to ground = 3.4 ohms +/- 10% @68F 20C
 
Ignition Source coil = Brown to Ground = 166 ohms +/- 10% @68F 20C

My 77 DT400 meets these specs.
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
23 Feb 2021 21:18 #17

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

Thanks. My coils meet all of these specs. The new cdi box did not solve the issue.

I have a NOS pulsar and source coil on the way just to see.

I can't think of any way my flywheel would cause an issue.

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24 Feb 2021 06:41 #18

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

I had an inconsistent spark after rebuilding my 78 DT400. I checked everything and I was left with the conclusion that the CDI box was bad. I replaced it and still had inconsistent spark. As a last resort I went to pull the rotor of f to inspect the components and discovered the flywheel key was sheared off. Replaced the key and problem solved. Just something else for you to check.
1978 DT400
1975 DT250
1976 YZ125C (in progress)
1976 YZ125X (in progress)
2018 YZ250FX (my race bike)
2010 Triumph America (my cruiser)
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25 Feb 2021 18:29 #19

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