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Makotosun

DT400 Revs Hanging

  • hatrick1960
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DT400 Revs Hanging was created by hatrick1960

Hi,

This has probably been covered before but my DT Revs 'hang' and then drop back down again if I pull the clutch in?
Also should you b e able to 'red line' these bikes, I struggle to get past 6K?
Thanks
16 Dec 2021 05:08 #1

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Replied by Pedalcrazy on topic DT400 Revs Hanging

Others will come along I’m sure but…I think folks here will say you may have a small air leak somewhere. Could be rubber intake manifold or crank seals. I have both a DT400C and DT400E and will red line in lower gears. Top gear would be 80+ MPH and haven’t gone there! I recall some of the experts saying the big bores don’t like revving out and I agree.
1978 DT400E
1976 DT400C
1973 RT3
1971 RT1B
1968 DT1 (3)
16 Dec 2021 08:34 #2

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Replied by GaryDean on topic DT400 Revs Hanging

Hi
Ive recently had this issue and there is a recent thread on it on this site. basically I did all the usual checks, seals inlet manifold etc, ignition system. my problem was the carb, it had the wrong jets it, I cleaned the carb, went back to stock jets and set the idle mixture jet at 3/4 of a turn out instead of 1 1/2 turns and problem went. the bottom end is a little gurgly but no hanging or over run, its a small price to pay
16 Dec 2021 08:36 #3

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  • hatrick1960
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Replied by hatrick1960 on topic DT400 Revs Hanging

I actually took the bike to a 'two stroke' specialist and they checked the carb out and said everything is as it should be - correct jets etc and all clean. He said definitely not crank seals so I'm guessing maybe the rubber inlet from the reed valve to cylinder head?

Is it worth putting after market reeds in?
Last edit: 16 Dec 2021 09:59 by hatrick1960.
16 Dec 2021 09:57 #4

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Replied by Blackhat250 on topic DT400 Revs Hanging

Spray easy start  around carb boot etc, or remove  flywheel cover spray at crank seal area,  [ bike running ],,  soon see ,
If you aint mixin gas " you aint haulin Ass
16 Dec 2021 11:57 #5

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Replied by Jammyyammy on topic DT400 Revs Hanging

One of the air leaks on my DT400 was where the two crankcase halves join together - near the front engine mounting.
16 Dec 2021 16:07 #6

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Replied by hatrick1960 on topic DT400 Revs Hanging

How did you find the leak?
17 Dec 2021 05:33 #7

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Replied by Gr8uncleal on topic DT400 Revs Hanging

It's not something daft like a sticking or incorrectly routed cable, is it?
17 Dec 2021 06:53 #8

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Replied by msavitt on topic DT400 Revs Hanging

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air leaks bad!
17 Dec 2021 08:27 #9

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Replied by GaryDean on topic DT400 Revs Hanging

I put carbon reeds in mine as the thought of 47 year old stainless ones being case hardened going into the pot would be a bad day
17 Dec 2021 08:31 #10

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