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1977 dt400 running issues

09 Sep 2020 08:31
motox500r
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1977 dt400 running issues #1
bike will start up idle have full throttle response for about 20 seconds then throttle response is gone [just goes flat], also more exhaust smoke at that point, changed the crank seals twice already and have the o-ring behind the primary drive gear installed, floats are good ,reeds good. is there any other route other than the crank seal for a point of entry for tranny fluid?, getting frustrated with this one as i am so close, any info appreciated., Thanks

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09 Sep 2020 10:05 09 Sep 2020 10:06 by RustiePyles.
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1977 dt400 running issues #2
Is your trans fluid level dropping, does the smoke smell like two stroke oil or primary oil? Could be a leak at the case mating surface. Is it only smoking more when your on the throttle? when you twist the throttle your injecting more oil. What do the plugs look like? Is your autolube pump adjusted correctly?

Fletch

1975 DT175B
1979 XS650
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09 Sep 2020 11:44
MarkT
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1977 dt400 running issues #3
My guess is it might be a CDI problem? Clean all the connections and cross your fingers.

Using a timing light might help figure it out.

It could just be going "rich" and rich fuel is the #1 reason for excessive smoke if all else is good.

Here's a video of a bike with a known bad CDI. This one was real bad. Wouldn't rev at all.

Posting a video of yours might help someone diagnose your 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
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09 Sep 2020 12:41
run103
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1977 dt400 running issues #4
what kind of air filter are you using. Take the filter right out and run it and see what happens. You cannot use twin air with lots of the new stickey oil on them.
Doug
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11 Sep 2020 09:27
motox500r
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1977 dt400 running issues #5
Going to post it this weekend, really appreciate the help.

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11 Sep 2020 14:13
motox500r
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1977 dt400 running issues #6
Will post a video this weekend

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11 Sep 2020 17:49
RT325
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1977 dt400 running issues #7
I seem to be stuck on exhausts lately, so, don't suppose there's a random carbon lump bouncing around looking for a baffle or spark arrestor to plug. Then a good rev lodges it in the spout & constipating it. Could smoke more at that point if holding the throttle open for a bit. Alternatively has the motor got a belly full of oil gravity fed from the oil tank & just needs bringing up slowly to clear it then give a big rev. Then again,Maybe not. Look forward to the video.

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14 Sep 2020 04:58
motox500r
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1977 dt400 running issues #8
didn't get a chance to do a video but this is what it looked like before I changed the crankcase seal, I'm thinking I compromised it as it has the same symptoms, thanks for video most useful if I get past this and still have that problem.

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15 Sep 2020 10:58
motox500r
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1977 dt400 running issues #9
K&n ran good for Abit with it, still learning towards the crankseal have OEM on the way.

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15 Sep 2020 12:38 15 Sep 2020 12:53 by motox500r. Reason: More detail
motox500r
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1977 dt400 running issues #10
Pipe burned out upon rebuild. Trying to post a video to no avail. File may be to big will downsize an give it a go.

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