Two stroke advice needed please

[Aidan1150]

My boss ended up with a DT125 Yamaha as part of some deal or other and has asked me to MOT and sell it for him.

It's a 2002 single cylinder 2 stroke and is in pretty good condition overall. A casual glance at it on Friday evening suggested that new pads, plug and a chain & sprocket kit should have it about ready for sale.

So, yesterday I rode the DT the 10 miles from work to my house, but the wee bike wouldn't pull top gear at all. It's a peaky little motor, nothing much happens until the revs cross 6500 and at 7000 it goes pretty well up through the gears, until you put it into top that is, when the revs drop off quite dramatically and you have to drop a few gears to get it buzzing again. On downhill sections it would travel on quite well in top, but come the flat or a bit of an incline and it would drop off the boil again.

It's many many years since I rode a little stroker and my knowledge of them is not great, so have any of you any suggestions as to what the matter might be and how to rectify it?

Thanks in advance.

 

[Timolgra]

It may have a restrictor fitted, need a rebore or rings and I think they have issues with the power valve.......of course it's only a 125cc..designed for the more svelt rider

 

[iftikartaxis]

check the exhaust could just be coked up do the baffles come out
also if the bike has been stood a while dump the fuel

my mate spent a day trying to get a scooter running he tried everything
i asked if he had checked the simple things first
he put some petrol in the exhaust after removing it set the fuel on fire and it burnt the crap away the scooter ran like a well oiled watch after that

"Praise the lord and pass the Ammunition"

 

[Fanum]

It's many many years since I rode a little stroker and my knowledge of them is not great, so have any of you any suggestions as to what the matter might be and how to rectify it?

Thanks in advance.

Sir wouldn't by any chance have changed shape and size marginally over those intervening years would sir???

It's an old 125 Aidan.......of course the wee bugger's gonna struggle to pull in top with you onboard

 

[Possu]

If the engine is good, just check the sprockets to confirm that someone's not cocked up the gearing.

 

[Deleted account 220427002]

If the engine is good, just check the sprockets to confirm that someone's not cocked up the gearing.

that was my guess... some young pup wanting more top end

14-49 standard i think

 

[GS TRV]

It's doing to move at all with a GSer on board

 

[Aidan1150]

It may have a restrictor fitted, need a rebore or rings and I think they have issues with the power valve.......

Thanks Tim, that's a few things to look at.

of course it's only a 125cc..designed for the more svelt rider

Sir wouldn't by any chance have changed shape and size marginally over those intervening years would sir???

It's an old 125 Aidan.......of course the wee bugger's gonna struggle to pull in top with you onboard

I'm a rather svelte 16 stone Tosser I'll have you pair of barstewards know.

I think I'll go with a new standard C&S kit first and see how it goes then. Thanks for the suggestions all, keep them coming.

 

[vilguy]

Aidan, is the powervalve functioning correctly? It should go "whirrr whiirrrr" when you turn the ignition switch. Even if there is that noise, whip the powervalve cover off (l.h side i think from memory) and check the system is working and that the cables arent snapped.

Alot of DTs were not derestricted as not all were fitted with the powervalve servo.

I grew up on DT125s

 

[DrFarkoff]

TAke the rear muffler section off an go for a run then

Over 5,000 miles and cheap oils bung up the silencers

I had a neighbour with a wee 2 stroke and they had paid a fortune to garages to cure it and 240 quid later it was no better

Derbi senda 50 with 80 kit fitted and wouldn't do 20 in top the lad was 14 stone

Fault = rear pipe section where it reduces between expansion and muffling had coked up reducing gas flow to about 6mm and it should have been nearer 15mm

Cure was to cut bad bit out and bale into fire for 10 minute shake out carbon and reweld back in After cure and a wee fettle , 83 km/h with 20 stone on the flat

 

[Aidan1150]

Thanks Vilguy and Jay.

The wee bike has been lying in the shed all winter, so I need to get my finger out and get it running, MOT'd and ready for sale.

 

[MCD motor cycle delivery]

sounds to me as if the power valve is not working...try removing the valve cover and turn the valve 180 degrees, i remember my lad doing that on his DT and it was a little rocket ship and high revs.....but saying that i think his was a 99/2000 model...might be a different set up on the later models..

 

[Flipfly]

Very few DT's had the servo fitted as you legally were only allowed to have it fitted once you'd past your test.

Most of the lads used to peg the valve slide in the uppermost position. This free'd up the top end at the expense of the bottom end, but at 17 ya always ride flat oot so it never seemed a problem

Have the powervalve cover off (on the cylinder head just behind the exhaust) and have a peek in there too. It can get might gunged in there too.

My guess would be shite in the valve, valve in it's low position and the exhaust being full of crap.

Pop the exhaust off at the front too. Don't know what year it changed, but there used to be a restricor pipe welded in the front pipe to restrict it too. you'll see 3 spot welds if the pipe is there. It's a B'stard to remove (when you're 17 and as daft as arseholes ) but well worth the effort. My LC would top a ton on the clocks (and it was deadly accurate )

 

[vilguy]

Most of the lads used to peg the valve slide in the uppermost position.

i did that just that! them were the days... few scraps from my dads drawer of bolts and wedged em in to stop it moving happy days.

Mind it was shite low down but as soon as you got to around 7k .. BBWWAAARRPPPPPP

As mentioned rip off the cover, and if there is no servo, remove the powervalve holder and twiddle it clockwise then rev it again, you should be able to tell the difference.

...sigh... i want one again now!!!!!

Lets all by dtr125s and go bombing round the forests!

 

[Flipfly]

i did that just that! them were the days... few scraps from my dads drawer of bolts and wedged em in to stop it moving happy days.

Mind it was shite low down but as soon as you got to around 7k .. BBWWAAARRPPPPPP

As mentioned rip off the cover, and if there is no servo, remove the powervalve holder and twiddle it clockwise then rev it again, you should be able to tell the difference.

...sigh... i want one again now!!!!!

Lets all by dtr125s and go bombing round the forests!

Yep, sounds like a plan

Actually a very overlooked machine for green laning, but the frame is based on the YZ125 mx bike and the motor with the servo is an absolute peach.

I spent alot of my youth trying to make my stink wheels go faster. I had 85 out of my ZR50. I was being towed by my mates Fiesta after a botched porting job by an idiot 16 year old who thought he knew more than he did (not much changed apart from the age ).

 

[vilguy]

*sigh* happy days haha

I would happily buy one of the newer dts, they look really cool! espicially the latest 08 etc shape ones.

 

[garfield]

So, yesterday I rode the DT the 10 miles from work to my house, but the wee bike wouldn't pull top gear at all.

Aidan on a 125cc ....it'd be like a Moose riding a tricycle....

.....

 

[Aidan1150]

It would suit you though.

Two strokes and you're away laughing. or so I've heard said.

 

[millard]

that was a wee gem

 

[Aidan1150]

I found that the two cables which operate the power valve were broken, so I got some new ones and fitted them.

Does anyone know how to set the power valve? I'm reluctant to start the bike and do harm until I know that the PV is correct.