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Makotosun

was reading where someone was trying to fix DT400b&c cruise surge ?

  • Don Dieago
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A while back not sure if here or somewhere else someone was tuning on their 400 to get rid of the constant speed cruising surge or lunge the 400 does? anyone know where or what Im talking about? Mine does it too it hates constant speed running but it loves traffic ticket kind of riding. It seems he was saying he helped it alot. I would like to read it again.
If I could find it
Last edit: 27 Jul 2019 15:04 by Don Dieago.
27 Jul 2019 15:04 #1

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I don't recall the post but am following this in case it gets located. That is a really common problem with the DT400B/C.
IF it isn't one thing, it's another.
27 Jul 2019 15:57 #2

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Assuming there are no air leaks [ crank seals- carb boot- cylinder base ] ,start with closing the Air screw ,, till is stops bucking, if this improves the symptoms,, i would up the pilot jet a size,, them dial in the Air screw till its smooth ,.. you need All air leaks fixed first,
If you aint mixin gas " you aint haulin Ass
Last edit: 27 Jul 2019 16:54 by Blackhat250.
27 Jul 2019 16:52 #3

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Two thoughts, it's either slightly rich or slightly lean. so try clip up a notch & clip down a notch & you should notice the difference straight away in the cruising area.
27 Jul 2019 17:03 #4

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Its not really a problem as much as a trait of the model I came upon and read a post somewhere where a guy made it 20% better just cant remember where. bike runs like heck if wfo dirt style riding or hot rodding is what you like
Last edit: 27 Jul 2019 20:58 by Don Dieago.
27 Jul 2019 20:55 #5

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Ive played with needle and everything new in carb and genuine mukuni. fresh piston/bore new crank seals new intake and fiber reeds. Runs damn good spins tire on pavement it just dont like consistent cruising at a maintained speed
27 Jul 2019 21:02 #6

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This link is one of many threads on the topic... common issue... last page has someone saying they have reduced the problem by "95%".

yamaha-enduros.com/index.php/forums/74-7...-up-to-snuff?start=0
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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27 Jul 2019 21:46 #7

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Thats it! Thank You!!!
27 Jul 2019 21:56 #8

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Back several years ago I spent a lot of time trying to eliminate my 400C bucking and surging. I had a notebook that I filled several pages documenting all jetting, needle and even needle jet changes, good and bad. The one thing that made the most difference was the throttle slide. The 3.0 was too lean and the 2.0 was too rich. At that time I could not find a 2.5 to buy so I cut the 2.0 to 2.5. I was 90% happy with it but it wasn't completely cured.
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28 Jul 2019 09:20 #9

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I have a 2.5 ordered
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28 Jul 2019 19:06 #10

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