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'75 DT 100 excessive smoking?

01 Jun 2020 19:28
Wandwuff
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'75 DT 100 excessive smoking? #1
Hello! My Dt100 is smoking way more than usual with the autolube system. I haven't changed anything but a carb rebuild so im not sure what it could be. The plug is fouled and i cant rev high because of it, could the issue be not revving enough so the oils not being burned fully? Or is there just too much oil? is there an easy way to tell if the autolube is pumping too much?

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01 Jun 2020 20:27
darinm
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'75 DT 100 excessive smoking? #2
Crank seal is the most likely suspect.

1972 Yamaha CT2 175
1972 Suzuki TS 185 Sierra
2016 Yamaha WR250R

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01 Jun 2020 20:46 01 Jun 2020 20:51 by Wandwuff.
Wandwuff
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'75 DT 100 excessive smoking? #3
Any way to confirm that? My transmission oil is the same level it's always been at

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01 Jun 2020 21:00
MarkT
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'75 DT 100 excessive smoking? #4
Thanks for posting the history. It's not the oil, it's too much fuel.

Did you put a "kit" in the carb with new jets? If so, put the original jets back in.

Also if the o-ring on the "jet setter" that seals the float bowl to the needle jet is missing, wrong, or damaged it will run super rich.

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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01 Jun 2020 21:11
Wandwuff
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'75 DT 100 excessive smoking? #5
No, it was the stock carb and i replaced or kept all the seals, as for the jets, stock that was in there was a 160 and i live at about 3700 feet elevation and it was running super rich to the point of not starting so i put the jets down to a 120.

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01 Jun 2020 21:36
darinm
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'75 DT 100 excessive smoking? #6
First, Mark knows more than I do so follow his thoughts first. If the crank seal just started going bad, you levels would not drop yet. Is it the typical color smoke or more white than normal?

1972 Yamaha CT2 175
1972 Suzuki TS 185 Sierra
2016 Yamaha WR250R

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01 Jun 2020 21:56
MarkT
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'75 DT 100 excessive smoking? #7
That's a huge jump on the main jet... which by the way, has nothing to do with starting. There's a Mikuni tuning manual in the tech library that might be helpful.

I'm still going to say "carb o-ring" or something wrong in the carb. Just a guess.

Hope you figure it out! :Buds

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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01 Jun 2020 22:06
Wandwuff
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'75 DT 100 excessive smoking? #8
it's blue smoke. I also went from 160 to 140 then to 130 to 120 then 110 then i settled on 120 so i didnt just jump, i spent a lot of time tuning. what is the "carb o-ring"?

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01 Jun 2020 22:34
Mothersbaugh
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'75 DT 100 excessive smoking? #9
#3 in the following diagram. must be in good shape, flexible and not cracked, or it will leak and cause what you are describing. Lube it just a little when you put the carb together each time.
www.partzilla.com/catalog/yamaha/motorcy...75/dt100b/carburetor

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01 Jun 2020 22:45
Wandwuff
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'75 DT 100 excessive smoking? #10
last time i had it apart that was in good condition, i guess ill check on it again

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