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Makotosun

73' DT3 250 Choke circuit issue Mikuni VM26SH

  • Dirtdad55
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Newly acquired DT3  and the symptoms are as follows:     Put the choke lever down , kick the bike several times  ( usually starts on 2nd kick or so ) and the bike starts but will die if I open the throttle.  I have to just wait , as the engine barely runs around 1200 rpms.  I wait for 1 to 2 mins till the engine is a bit warmed and then I can take the choke off and the bike then performs nicely up and down the street with a steady idle .    Am I losing suction somewhere in my choke circuit ,? I've cleaned carb several times now and closely looked at the start jet at the bottom of the carb     Any thoughts from the group ?      Thank you in advance  Tom
20 Oct 2022 12:05 #1

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Replied by Sneezles61 on topic 73' DT3 250 Choke circuit issue Mikuni VM26SH

One of us is wrong… my 72 RT2, up is enrichment… down is regular running…
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20 Oct 2022 13:53 #2

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Lever down for enrichment & up for normal running. I'd still go back to the fixed jet in the bowl cavity & probe it from both directions--side on where fuel leads to the jet & from the top looking down & probe it to size if you can find something that size. Then flush it & blow it both ways. If it's not that, then maybe left crank seal needs changing. Don't have idle set too high as choke relies on a closed throttle to suck. Alternatively can only think fully dismantle carb--everything out & probe or at least eyeball all jets & airways. Idle mixture screw no further out than 1.5 turns or try one turn initially. Air leak that bad would be obvious. I'm out of ideas.
20 Oct 2022 14:06 #3

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just talking about lever again, depending if ya talking the lever or looking at the plunger the lever lifts. I talk lever ya put your thumb on--push down for rich.
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20 Oct 2022 14:09 #4

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On my '72 DT2 lever up is regular running, lever down is enrichment. My bike also has the Mikuni VM26SH carb with the same #60 starter jet. I'd purchased a carb rebuild kit from Niche Cycles off eBay. One of the few parts that seem to work properly from the kit are those replaced in the choke.
Last edit: 20 Oct 2022 14:11 by Brzn.
20 Oct 2022 14:10 #5

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Replied by AirborneSilva on topic 73' DT3 250 Choke circuit issue Mikuni VM26SH

On all the DT's I have or had lever down is choke and lever up is normal running.
2023 Tenere T7
1976 DT400C
1975 DT400
1981 DT175H
1972 DT2 250
1980 GT80
1972 JT2
20 Oct 2022 15:31 #6

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Just to make sure I understand your question does your bike run normal when it is warmed up throttle response , rpm’s etc if so these are old bikes whether a Yamaha or Honda take several minutes to warm up. My Harley takes about  5 minutes to warm up
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20 Oct 2022 15:35 #7

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I was thinking the same thing... A couple of years ago I bought a 1971 Ford Ranchero "hot rod" that needs some work.

Brought me right back to what seems like yesterday... on a cold morning (where I lived in California it was fairly rare to get down to freezing temps so not exactly "cold" compared to other parts of the world) you needed to warm up your car before driving off.

Computers and fuel injection have really spoiled us.
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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20 Oct 2022 16:45 #8

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Replied by Dirtdad55 on topic 73' DT3 250 Choke circuit issue Mikuni VM26SH

Ht1kd  :   The bike performs well once I get through this warm up period.

Brzn:     So the rebuild kit you get from Niche cycle has parts for the enrichment circuit ?   I thought the enrichment jet
              was fixed in the float bowl and not able to removed ?  

I have the normal choke lever   down for choke  up for no choke
Also if it were a left side crank seal , wouldn't it idle poorly and not run too well ? 

Thanks for all your input ...
20 Oct 2022 18:43 #9

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How warm is it outside when this is happening?
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
20 Oct 2022 20:21 #10

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