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1983ish Yamaha DT 125 LC field bike

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as8v
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Joined: 13 Dec 2009
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PostPosted: 15:15 - 21 Dec 2009    Post subject: 1983ish Yamaha DT 125 LC field bike Reply with quote
Round at my girlfriend's parents farm, I dug out an old trail bike. Its been in a barn for 10 years and not moved since they got a quad bike.

Its had all the lights and instruments stripped off and has a few plastics missing.

https://i46.tinypic.com/15yd8k5.jpg

After dragging it out the barn, removing the minging air filter, checking for spark, draining stale fuel and topping up with some 2 stroke premix we ran it off and bump started it.

https://i45.tinypic.com/2r7x0dc.jpg

It ran but stalls on letting the clutch out. Also won't kick start. Gear selection is a little hit and miss.

I removed the carb and cleaned out a load of build up but ran out of petrol to try starting again.

I'm going to see if I can get it to run well enough to do a few laps of the field and then I'll strip down and give it some paint.

This just dropped through the door:
https://i45.tinypic.com/11w35sn.jpg
A Haynes manual of the old school where they actually show you how to strip the engine and gearbox right down.

Its never going to be road legal but I will use it for running round the farm and lanes on.

Starting a shopping list:
Air filter
Fresh gearbox oil
Chain and sprockets
Big tin of black hammerite

And probably a hundred other things when I come to take it apart.

First time I've ever had a motorbike let alone a 2 stroke water cooled beast so any advice appreciated. To be honest I was staggered the thing started and ran, now I have these wild ideas of rebuilding it.
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27cows
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PostPosted: 17:33 - 21 Dec 2009    Post subject: Reply with quote
Same (or at least extremely similar) motor as the RD125LC, which are extremely tough for pokey strokers. Not at all surprised it started up. I would go as far as to say that it'll probably run fine after a bit of tinkering.

Would recommend paying close attention to the alternator wiring (and alternator itself), the CDI, ignition coil, HT lead and the ignition switch wiring (if it has a switch). Some or all of these may have got the dreaded green rot in and will need careful cleaning up after standing for so long, most likely.

Rings might have become gummed after this length of inactivity, but I wouldn't recommend pulling the top end off until you're certain it's not a weak spark or carburation issue causing it to stall.
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as8v
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PostPosted: 19:57 - 21 Dec 2009    Post subject: Reply with quote
27cows wrote:
Same (or at least extremely similar) motor as the RD125LC, which are extremely tough for pokey strokers. Not at all surprised it started up. I would go as far as to say that it'll probably run fine after a bit of tinkering.

Would recommend paying close attention to the alternator wiring (and alternator itself), the CDI, ignition coil, HT lead and the ignition switch wiring (if it has a switch). Some or all of these may have got the dreaded green rot in and will need careful cleaning up after standing for so long, most likely.

Rings might have become gummed after this length of inactivity, but I wouldn't recommend pulling the top end off until you're certain it's not a weak spark or carburation issue causing it to stall.


Great - thanks for the advice! I've barely ridden a motorbike before let alone troubleshoot the engine - I'm more used to taking apart modern VW car engines with fuel injection and ECUs with helpful fault codes.

GF's dad says it was a good runner before laid up, although its always been a lazy starter. It was only laid up due to a quad being more use round the farm.

He has always used pre mixed 2 stroke oil in the petrol - on reading the haynes theres an oil tank, pump and I now know what the cable splitting off the throttle and going to the engine is - adjusts oil flow. Anyway, it doesn't look like any damage has been done to it by running premix since it started after all this time!

Luckily it escaped the damp and rot being in a dry part of the barn.

Electrics wise the spark didn't look terribly strong in comparison to what i'm used to seeing from car plugs so thanks for the heads up.

If I get it running OK without spending too much I'm going to clean it up and give it a coat of paint. Although I do kinda like the "used" patina......
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27cows
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PostPosted: 20:11 - 21 Dec 2009    Post subject: Reply with quote
Welcome to the world of bikes Very Happy You may find the bug bites hard.
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DeeTee
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Joined: 25 Dec 2009
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PostPosted: 22:50 - 25 Dec 2009    Post subject: Re: 1983ish Yamaha DT 125 LC field bike Reply with quote
as8v wrote:

It ran but stalls on letting the clutch out.

It may be fitted with a stand switch so check this is working correctly, you could bypass it just to get you going.
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ms51ves3
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PostPosted: 00:18 - 26 Dec 2009    Post subject: Re: 1983ish Yamaha DT 125 LC field bike Reply with quote
DeeTee wrote:
as8v wrote:

It ran but stalls on letting the clutch out.

It may be fitted with a stand switch so check this is working correctly, you could bypass it just to get you going.


A side stand switch would cut the engine out when he puts it into first gear, not when he lets the clutch out.
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johnsmith222
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Joined: 26 Dec 2008
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PostPosted: 01:57 - 26 Dec 2009    Post subject: Re: 1983ish Yamaha DT 125 LC field bike Reply with quote
ms51ves3 wrote:


A side stand switch would cut the engine out when he puts it into first gear, not when he lets the clutch out.


Unless you know that is correct for that specific bike, a side stand switch can cut the engine out when letting the clutch out.

The one on the ZZR6E does this. It is likely also wired up to the neutral light or something because you need to be in neutral to let go of the clutch with the side stand down.
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Jamie S
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PostPosted: 10:04 - 26 Dec 2009    Post subject: Reply with quote
Gears a bit hit and miss ? stalls when the clutch is let out??

Sounds like your clutch plates have stuck togeather.... wip the cover off and check that the plates are all free when the clutch is pulled in.
Jamie
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ms51ves3
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PostPosted: 10:58 - 26 Dec 2009    Post subject: Re: 1983ish Yamaha DT 125 LC field bike Reply with quote
david_m213 wrote:
ms51ves3 wrote:


A side stand switch would cut the engine out when he puts it into first gear, not when he lets the clutch out.


Unless you know that is correct for that specific bike, a side stand switch can cut the engine out when letting the clutch out.

The one on the ZZR6E does this. It is likely also wired up to the neutral light or something because you need to be in neutral to let go of the clutch with the side stand down.


Not on that DT as it won't have a switch on the clutch lever.
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as8v
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PostPosted: 11:06 - 27 Dec 2009    Post subject: Reply with quote
Great stuff! Heading back to the farm over new year so I've got plenty to go on now.

Thanks all!
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TUG
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PostPosted: 00:08 - 28 Dec 2009    Post subject: Re: 1983ish Yamaha DT 125 LC field bike Reply with quote
ms51ves3 wrote:


Not on that DT as it won't have a switch on the clutch lever.

As you would know i've not had many old bikes in my hands so i would think that as soon as he selects first gear his bike will cut out reguardless off clutch posistion. Thumbs Up
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Haz ER-5, innit!
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as8v
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PostPosted: 13:42 - 04 Jan 2010    Post subject: Reply with quote
Sum of my recent work:

Compression fine, oil tank missing completely hence mixing oil in the petrol. Apparently came that way from the motorbike shop so hopefully its jetted right.

Oh and the fuel filter was clogged so binned it and am awaiting a new one along with new spark plug and a few other bits.

Was far too icy outside to try and start it again.
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bradh511
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PostPosted: 16:08 - 05 Jan 2010    Post subject: Reply with quote
Before you put new filter in i would recomend removeing the tank putting bit of petrol in the tank.

Take the petrol tap completely out as they usualy have filters in. so basicly swill the tank and clean the tap filter as you will be wasteing a new filter if more shit is in the tank Smile

Edit: Gear box oil is prob fucked after 10yrs ( gear problem ) or could be selector drum is warn if they have one :S . Also if you fill the bike with water dont forget anti freeze.

Sorry to be obvious

Have Fun
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as8v
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Joined: 13 Dec 2009
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PostPosted: 09:31 - 06 Jan 2010    Post subject: Reply with quote
bradh511 wrote:
Before you put new filter in i would recomend removeing the tank putting bit of petrol in the tank.

Take the petrol tap completely out as they usualy have filters in. so basicly swill the tank and clean the tap filter as you will be wasteing a new filter if more shit is in the tank Smile

Edit: Gear box oil is prob fucked after 10yrs ( gear problem ) or could be selector drum is warn if they have one :S . Also if you fill the bike with water dont forget anti freeze.

Sorry to be obvious

Have Fun


Hi Brad thanks for that, I have swilled the tank round with the old petrol and and drained it. I never knew there was a filter in the tap so I'll remove that and clean it.

I took the cap off the gear oil and peered in, it looked kinda milky. The haynes says I need 10w30 oil but I can't find any cheap stuff - I might just use some 10w40 supermarket car engine oil until I get it ridable and then refill with the correct weight. That should help flush the manky old stuff out too.

I was well surprised that after sitting so long the engine / rad didnt have any cracks or leaks from frozen water damage - whoever filled it last must have put a strong mix in!

I'll put some antifreeze in when I get round to blasting the cooling system through Smile
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as8v
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PostPosted: 09:34 - 06 Jan 2010    Post subject: Reply with quote
I'm thinking about colour schemes (ahead of myself I know).

1) Gloss black frame and Matt Black tanks and mudguards
2) Terminator 2 eighties style red and white
3) Camo matt greens

What do people think? Or should I just clean it and leave the "patina"!?
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27cows
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PostPosted: 06:24 - 08 Jan 2010    Post subject: Reply with quote
I don't think the colour scheme matters for off road only use - it will mostly be covered in mud Laughing
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