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New member from Colorado, USA. 1981 DT175H, less than 1K

30 Jun 2020 19:15
Red81
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New member from Colorado, USA. 1981 DT175H, less than 1K #1
Hello everyone, and let me first thank you for the help I have already received by reading this board. I am a new member, a brand new rider, and only young at heart. I bought a nice 1981 DT175 from my uncle (who is downsizing his fleet). The bike has less than 1000 miles on it, and looks like it has been used gently. My first question for you all is about jetting this bike for my area. I am near Denver, Colorado (5300 ft. elevation) and my parent's cabin sits at 11,200 ft. I tried the bike out at the cabin and had lots of fun, but I suspect that I need to jet it for higher altitude. I cleaned the carb while addressing a leak and noted that the main jet is a 130. To idle properly I need to turn the throttle screw all the way in as it is so I think the pilot jet is a bit big. Anyone want to take a guess at a pilot jet size I should try (and if I should step down from the 130 on the main). I see that the stock main jet is 150, so I think it is already better set for my altitude, but I think I should do more. Thanks!
Pete

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01 Jul 2020 00:20
Gr8uncleal
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New member from Colorado, USA. 1981 DT175H, less than 1K #2
Welcome! from Salisbury, UK.

An expert will chime in soon to answer your query.

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07 Jul 2020 09:53
Red81
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New member from Colorado, USA. 1981 DT175H, less than 1K #3
bump this to see.

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07 Jul 2020 11:31
MarkT
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New member from Colorado, USA. 1981 DT175H, less than 1K #4
Need a picture identifying which screw you are turning all the way in to get it to idle.

Idle air screw is capped from the factory and might not be visible.

If it's the idle stop screw, which I suspect it is, most likely you have a clogged pilot jet. Pilot on that model is already tiny for emissions... 22.5. Not likely you'd need smaller.

Other possibility is someone has already changed the pilot jet as you say they've changed the main?

What about the slide needle, slide needle clip, and needle jet sizes?

Completely and thoroughly cleaning carb (including removing the needle jet on that model) and finding out exactly what you have as a starting point are the first steps.

Next is identifying what "problem" you are having and what throttle opening it's occurring at.

As far as your main jet? Usually with altitude the temp drops too which offsets the change in altitude. Going from a 150 to a 130 is already at the "lean" side. And keep in mind that the main jet is mostly effective only from 3/4 to full throttle. If the slide needle or needle jet have been changed (and they should be) then something like a 135 or 140 main might be better.

Often the only change needed is a clip adjustment on the slide needle... Then maybe down a size or two on the main. The challenge is if you go to low altitude, you need to richen back up.

Last thing is these bikes aren't powerful by modern standards. Even a 400 will feel anemic at 10,000 feet compared to lower altitude. You simply lose power at altitude. You can't get that power back by jetting changes.

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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