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Out on the road! (And fiddling with the carb)

24 Mar 2020 14:55
Eazy-X
Sportsman
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Out on the road! (And fiddling with the carb) #1
Went to the garage (gas station) to get some fuel on my DT175 Yay2

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Originally I had a Chinese copy of the original VM24SS that the bike would have started with. Shock news! I got nowhere with it. What came with the bike was a Mikuni VM28 of some sort (similar to the Mikcarb on an Enfield Bullet) and that seemed to work a lot better...

Journey to the garage: brilliant, very easy going bike, love it! Only got it up to third gear but I probably shouldn't push it too much on brand new tyres. Note at this point the bike was running on fumes: a mixture of stale fuel and some premix (2 stroke oil pump also working so plenty of smoke!)

Fresh fuel in and the bike started stuttering on the way back. Couldn't get much above 3K. Oh yeah, if you read my other thread I swapped out the "mirror image" tacho gear parts and my tachometer now works :) Limped home in 2nd but as it's all suburban road (and quiet for some reason) no biggie.

Observations: good run, bad fuel. Bad run, good fuel! Starts and idles fine, won't start with choke. Last time I cleaned this VM28 I noted a #130 main jet (factory spec is a #140 in a VM24SS) and the pin was set as high as possible (clip at bottom.)

As it's the mid-range that has trouble that says to me main jet + needle adjustments. I'm thinking throw in a #140 + reset the pin to the middle position. Would welcome any suggestions of course!
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24 Mar 2020 15:52
darinm
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Out on the road! (And fiddling with the carb) #2
I'd stay away from adjusting both at once. Start with the needle until the mid range clears up and then see how the top range is and adjust if necessary.

1972 Yamaha CT2 175
1972 Suzuki TS 185 Sierra
2001 BMW F650GS
2006 Yamaha XT225
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24 Mar 2020 18:30
MarkT
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Out on the road! (And fiddling with the carb) #3
Congratulations!

(I'd start by lowering the needle one notch at a time...)

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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28 Mar 2020 10:10
Eazy-X
Sportsman
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Out on the road! (And fiddling with the carb) #4
I thought I got it running well. The #140 jet seemed, initially at least, to give me a bit more power over 4K. Went round the block and even thought to myself "calm down! new tyres, if you recall" :)

Just got round the bend a few hundred yards from my house and it spluttered. Started again first kick - I really don't think there's any problems with the pilot jet, mixture screw or idling speed - a cough @ ~3K, then it revved fine, then it coughed again. I stopped at that point and at least found out it's an easy bike to push!

So, from cold fine. After a good warm-up mid-range goes rough. Any thoughts?

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