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TOPIC: 1980 DT125G

1980 DT125G 25 Apr 2019 17:43 #1

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Hello! I have picked up a lot of great information here and have a couple questions regarding my DT125G. It's a resto project that I pulled out of a field which unfortunately had all of the accessories removed to make it more of a dirt bike.

I'm looking for a Speedo/Tach that would work with the factory lines that don't cost a fortune. Would any mechanical gauges work? (two stroke only?)

Also - my monoshock seems very bouncy, is this normal or does it need a rebuild? (Are they nitrogen filled?)
Thanks!
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1980 DT125G 26 Apr 2019 01:47 #2

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With the monoshock, if it bouncy as in returns instant with no damping resistance then yes--needs a rebuild. Also they were pretty prone to wearing outs swing/arm bushes but that opens another can of worms as the arm bolt often seizes solid in No3 with rust. The bits the bushes run on are part of that spacer where usually they're separate but makes no difference if it bound up solid. You'll soon know if you loosen the nut & try to tap the bolt back. If it moves then take the arm out while you have the chance & grease all moving parts where the bushes pivot plus grease the bolt even though nothing moves on that when tightened up as that's often where the problem starts. We used to pull all that apart on assembling new bikes to avoid all the drama in the future as usually we'd be selling them to farmers & it;d be all downhill from there lol. More the 175's but same horse.
www.partzilla.com/catalog/yamaha/motorcy...1980/dt125g/rear-arm
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1980 DT125G 26 Apr 2019 08:12 #3

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Yeah I attempted to remove that bolt a few weeks back. It was seized so badly I decided to wait for a rainy day. Thanks!

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1980 DT125G 26 Apr 2019 08:15 #4

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One last thought - would it be better to soak it down for a few days or is heating it up acceptable?

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1980 DT125G 26 Apr 2019 15:12 #5

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Yes they can be a real problem. soaking can't do any harm but i've not had any luck doing that, but at work we didn't have time to wait with days of soaking etc. What we used to do is lay it over onto a steel pipe with a foot & sitting on the concrete then other end 'nut end' i'd have something solid like a big crank pin with a long handle welded to it. Then get someone to hold that & belt it with a steel sledge hammer. Nearly always works, the old 'shock treatment trick'. Ok it'll make a mess of the threaded end although not like hitting the thread direct, but worry about that later. Have had many cases thinking back where we had to drill slowly straight in the end with a big slow drill we had where you could stand over top of it with two handles & put pressure on it. Had to drill in from each end bigger & bigger till it disappeared & cleared the frame each side. Sorry if that sounds like scare tactics but that's what we were up against with farm bikes running knee deep in cow crap & mud all day long

Re- heating up--there's probably nowhere you can heat it effectively to release the swing/arm axle from within the spacer/sleeve thingy. Hope yours is only a minor case of 'tight'. Just sit something solid against it & give it a practice tap--might get lucky.
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Last Edit: by RT325.

1980 DT125G 12 May 2019 05:34 #6

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Update: I'm still looking for a new shock, but I finally got a new wiring harness on the bike and it's running. However, it's very smokey in it's current state. I ended up deleting the oil pump and premixed it 40:1. It has fresh crank seals and the exhaust smells super oily (I'm guessing rich?) Hoping i can get it fixed without ordering new jets. Anyone have an idea where I should start?
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1980 DT125G 12 May 2019 06:42 #7

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Gmorning! Few things to think about till the better minds get around. Have you burnt out the exhaust pipe? Probably the culprit. Is there oil pooled up in the the bottom end? Dunno if that’ll cause it. If it’s rideable, take it out for a good rip and maybe it will clean up. On premix, it’ll be smokier at idle than when being ridden, I think. Good luck
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1980 DT125G 12 May 2019 06:58 #8

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You can check the jets in the carb and if they are stock, there should be no need to re-jet. Switching to premix already leaned out the air/fuel ratio as the mixture is thicker than straight gas and some of the gas is replaced by oil.

Premix will smoke more than the pump as already said. 40:1 might be lean on the oil depending on what you're using... these air cooled engines like and need more oil than water cooled. I wouldn't mix any leaner... 32:1 is what most use.

If it's been sitting, just go on a nice long high speed ride and the smoke should clear up.

Also make sure the air filter is not over-oiled or bad. If excessive smoke continues, keep an eye on the trans oil level.
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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

1980 DT125G 12 May 2019 07:12 #9

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Yeah when I took my first ride on it a couple months back i was 99% sure my crank seal was the culprit, so I replaced both. However when i first got the bike the entire bottom end was absolutely caked in 2 stroke oil. The pump had gravity fed into the engine and the stator seal eventually gave way and filled will oil as well (which i replaced.) I know it's a silly to ask about smoke with knowing about it's history, but I mean it smokes so much it looks like a barn fire!

So I referred to my manual and all it says about the jets are #120 for the main and #20 for the pilot and starter jet. Does that sound about right?

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1980 DT125G 12 May 2019 08:48 #10

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Another update: The jets were correct and I took everyone's advice and warmed it up. This was the first warm up it's had since 1983 and I was a little skeptical, but after maybe 3 minutes the exhaust cleared up and ran 100% normal with choke. It would die a few times with the choke off which made me think the pilot was clogged but it ended up running normally in the end. I even took a few laps around the backyard! Still have that shit eating grin on my face to prove it :D
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