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Makotosun

'78 DT400 Idle question

  • RamadiRat
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'78 DT400 Idle question was created by RamadiRat

This is a fully warmed bike, she starts on the 2nd crank pretty reliably, pulls great. Just not sure what this pulsing idle could point to, I am not certain I have the air/fuel/idle adjusted correctly... 

Video: youtube.com/shorts/LM-qwlNhRcQ?feature=share
18 Nov 2023 15:09 #1

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Replied by RT325 on topic '78 DT400 Idle question

Thanks for the Vid.
To me it just sounds terribly lean.
Shortest answer i've ever given haha.
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18 Nov 2023 16:41 #2

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Replied by RamadiRat on topic '78 DT400 Idle question

Might be the best answer ever! we'll see
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18 Nov 2023 16:55 #3

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Replied by Wrench66 on topic '78 DT400 Idle question

Classic lean idle drone sound..... richen up your idle mixture a 1/4 to 1/2 turn, IF it can't be richened enough before getting close to closing the air screw then richen the pilot jet one size (or two sometimes). You want that nice bubble sound :)
This video shows about what you want.
The later street two strokes (Dt's and the RD's) were leaned out a bit much for me..lol.
Good luck-- Ray

Nothing makes me smile like the smell of Blendzall green label ;)
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21 Nov 2023 11:25 #4

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Replied by RT325 on topic '78 DT400 Idle question

Yep exactly as WRENCH66 says.
Not a 400 but same end result of a good mixture setting.
Yours being so lean at idle [& even higher up above a proper idle].
'i think' you'll need to go up in pilot jet size by quite a bit [or it's almost blocked--something to check first].
On listening to the original video again, it answers to throttle positively, so re-thinking that it's all pilot related.
Have you had the carb right apart, needle jet [emulsion tube] right out to inspect plus check airway to 'that tube' although a blocked airway would make it richer up towards & also when the needle taking over.
The pilot outlet hole to the venturi on the motor side is on an angle & the progression hole is straight up, but both fed by the pilot jet & could get blocked or restricted although unlikely.
Float level not so low the pilot can't find the fuel?.
If [in my opinion] the pilot jet is big enough & sounds about rich enough at 1.5 to 1.75 turns out then turning it right home should just about stall it from richness [if its idling slow enough in ther first place].
Last edit: 21 Nov 2023 16:32 by RT325.
21 Nov 2023 16:14 #5

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Replied by MarkT on topic '78 DT400 Idle question

With the idle speed so high, my thought is air leak.
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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21 Nov 2023 16:34 #6

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Replied by RT325 on topic '78 DT400 Idle question

Trye that!!.  edit Meant 'True that'!!--I go for hard stuff first lol then find its running out of gas.
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Last edit: 21 Nov 2023 22:53 by RT325.
21 Nov 2023 16:39 #7

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