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1978 DT400 wiring harness 1M2-82590-52-00

  • msavitt
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Correction to subject line which should read "1978 DT400 wiring harness 1M2-82590-52-00 

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Hi there,
It would be incredibly useful to know what differences exit between the subject harness 1M2-82590-52-00 on 1978 DT400 and harness 1M2-82590-21-00 on 1977 DT400

sorry - had a few pops and really screwed this note up

thank you,
Martin
Last edit: 12 Sep 2021 23:36 by MarkT.
12 Sep 2021 22:12 #1

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Replied by MarkT on topic 1978 DT400 wiring harness 1M2-82590-52-00

77 had a headlight on-off switch in the handlebar switch...  several extra wires for that.

78 had the "always on" headlight as mandated by US law.  Taillight comes on with ignition on and headlight is on when you start engine.

So some fairly significant differences.
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
13 Sep 2021 01:34 #2

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Replied by Gr8uncleal on topic 1978 DT400 wiring harness 1M2-82590-52-00

Also, I think that CMSNL show two other variants of the 1M2-82590 harness.
Last edit: 13 Sep 2021 02:11 by Gr8uncleal.
13 Sep 2021 02:10 #3

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Replied by msavitt on topic 1978 DT400 wiring harness 1M2-82590-52-00

thank you Mark and GR8uncleal, your detailed knowledge never ceases to blow me away
VIN says bike is a 1978, but left hand switch has an on-off.
existing wiring harness could be repaired, but I found a '77 harness that looks about 100X better for $80 so we will see....my thought, assuming '77 is intact, is to work a few exceptions vs. fix what looks like a lawnmower accident
13 Sep 2021 11:08 #4

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Replied by Pedalcrazy on topic 1978 DT400 wiring harness 1M2-82590-52-00

As you know all the blue plastic is 77 too so somebody did a frankinbike from a 77 they had. The VIN tells the true story.
1978 DT400E
1976 DT400C
1973 RT3
1971 RT1B
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13 Sep 2021 16:10 #5

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Replied by MarkT on topic 1978 DT400 wiring harness 1M2-82590-52-00

Curious if you have CDI or points ignition.  Blue bike would have been a 250 with points.  So you might have a 250 harness and not a 400 harness.
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
13 Sep 2021 18:39 #6

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Replied by msavitt on topic 1978 DT400 wiring harness 1M2-82590-52-00

Pedal crazy engine and frame vin 1978. rear fender yellow, front blue, no side covers. And you were right - geez this bike has lots of parts!!!

Mark it’s CDI, 

I had a success today - inner fork tubes perfect over entire seal area so one in the win column!  This is a good bike that’s been worked on over the years by unfortunates who could have badly used this group and website!

Yamalube spec lower than ‘74 360 which has basically same rotating assembly. Was this due to tighter  EPA limits?  Seems stupid to feed slightly larger engine less oil 
13 Sep 2021 22:02 #7

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Replied by MarkT on topic 1978 DT400 wiring harness 1M2-82590-52-00

For the oil pump, are you only looking at the pump output spec per 200 strokes?  That's not the whole story.  Need to look at the big picture.

Have you thought about the fact that the DT360 has the pump driven directly off the end of the crankshaft?  One to one ratio.  At 5000 crank RPM the oil pump is spinning 5000 RPM

Later (monoshock) DT400 had the oil pump driven from an 18 tooth gear driven by the 25 tooth crankshaft gear.  About a 1.4 to 1 ratio.  At 5000 crank rpm the oil pump is spinning ~ 7,000 RPM.  Big increase in pump speed compared to the DT360 at any given RPM.

With the pump spinning faster, the pump output per 200 strokes needs to be reduced just to give the engine the same amount of oil for the RPM.

I'm not saying Yamaha didn't cut back the total amount of oil slightly on the later DT400...  they could have cut it back slightly...  just not nearly as much as the "200 stroke" spec might lead someone to believe. 

Oils were getting better and more available.  (In early 70's regular motor oil was used a lot because two stroke oil wasn't on every shelf...  by the later 70's it was a lot easier to buy two stroke oil at gas stations and even grocery stores.)  And maybe it had something to do with the EPA.  But in my opinion Yamaha certainly didn't do anything "stupid" even if they did reduce the oil amount slightly.

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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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13 Sep 2021 22:57 #8

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Replied by msavitt on topic 1978 DT400 wiring harness 1M2-82590-52-00

wow, thx Mark
I didn’t factor that gear reduction into my thinking. 
I am beginning to suspect you were a Yamaha engineer!
14 Sep 2021 00:28 #9

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