Hi Chaps

i've just got my '89 DT 125 R, it was running fine but all of a sudden when riding it for the first time it totally cut out. It did not have any power at all then twisting the throttle. I stopped at the side of the road and it stalled, I kick started and it started first time, then ran fine again.

I thought something could be blocked so i have cleaned the carb and the jet. I took it out for another ride and for a while it was fine totally back to normal. After about 30 minutes of riding it totally lost power at 7000 RPM, it sounds all spluttery through all gears and as it approaches the power band 7K it is awful! Now it seems to struggle to get to 40mph, very spluttery and does not go past 7000rpm.

It came de-restricted witha DEP exhaust and im pretty sure he has done something power valve too.

Any help would be greatly appreciated.

Thanks

well it seems like last time by working on the carb you fixed it, i'm wondering if you have water in the fuel...drain the carb bowl and try it again, you can usually do this with the carb insitu so it's an easy fix.

cheers oldgit, if this keeps happening (the guy who had it before also cleaned the carbs for the same fault) what else could it be? Maybe the fuel filter? or is just a case of clearing all the crap out then it will stop happening? This bike was stood in the guys garage for 6 years! Eeek!

if draining the bowl fixes it, albeit temporarily you need to drain the tank completely, even take it off and shake out the last...

I checked the spark plug before doing the bowl and it was buggered coaked and wet. Changing to for a new one has resolved this fault.

Thanks for your help OG,

hmm, the very next day after i changed the spark plug the issue returned. I checked the plug again and it was coaked black again!

Is it running rich or lean?

im going to give it some love this weekend my plan is;

Clean air filter

Clean fuel filter

Clean baffle

Clean carb bowl

If these don't resolve it, should i take a look a the fuel/air mixture screw? or could it be a worn piston ring letting oil through?

Cheers

i'm afraid it may need a new crank seal (clutch side) and so is therefore burning transmission oil!

Can i check anything to see if it does need a new crank seal? Is this something a inexperienced mechanic (me) could do?

i wouldnt recommend that an inexperienced mechanic could do this myself?

as for pointers

take out the oil filler...can you smell petrol?

smoke from the exhaust...is there lots of it that doesnr really clear when the engine is hot?

transmission oil level...is the level falling with prolonged use?

Excellent thanks OG.

I have just noticed that there is a cable broken (leads into the head). I wonder whether this controls air/fuel/oil mixture?

that will be one of your power valve (PV) cables, performance will be badly affected with this broken

ahh i see, would it make it splutter an run really rough? this could be (one of) the isseues

yes it will run badly like this, get it sorted. there is a method to align the PV correctly when you get a new cable

Nice one, thanks a lot OG you're a star

i've just looked again the the wire is red and green and looks like it attaches to one of the head bolts, is this still the PV cable?

And also on the power valve its self there are 2 ports numbered 1 and 2, these dont have anything plugged into them, is this right? The haynes book has something plugged into both.

i've just looked again the the wire is red and green and looks like it attaches to one of the head bolts, is this still the PV cable?

And also on the power valve its self there are 2 ports numbered 1 and 2, these dont have anything plugged into them, is this right? The haynes book has something plugged into both.

Ahh my bad I was getting confused by the term 'cable' you mean an electric cable!

The cable in question attaches to the temperature sensor on the cylinder head...top right on this picture here

It seems you do not have a working PV, who knows there may even be no servo on your bike, the servo turns the power valve by means of cables and a pulley

you can see a servo (detached from the frame) here and the cables into the pulley enclosure

yep thats the puppy! so the temperature sensor is disconnected...its actually the metal bit coming out of the temp sensor which has corroded and snapped rather than the wire.

i dont have a case on my PV and there is definitely no servo attached. It looks like someone has put a screw in the pulley of the PV (jamming it open?) the pulley does not move at all when i turn the ignition on (but i take it this is normally controlled by the servo?).

I dont know what the guy did before he sold it to me but looks like he's well and truly bodged it . Balls looks like ill need to take it to someone in the know to see if there is anything else he has "modified" more money BOO!!

yeah they term it 'pinned open' they make the PV full open all the time, the consequence is lots of clutch slipping and plenty of throttle...good high revs power but poor low revs power. you need to check the loom connector that usually goes to the servi is intact and source a servo from ebay?

Got her going in the in end, took the carb out again and the bowl was full of brown shitty petrol, this should now be resolved as i have fitted a new fuel tank. Still down on power atm and it obviously running a little hot as the temp sensor is broken. Doesn't rev above 7K still which is a little concerning but no longer cuts out which is good. After running her for a bit the plug was nice and not covered in oil (when we took the carb out we adjusted the needle).

I'm not going to ride her again until i get my new temp sensor. I need a new air filter too, any recommendations?

Not starting again...this has to be the most unreliable piece of equipment i have ever had the misfortune to own

I have managed to borrow a compression tester so, ill check her out tonight to see if the rings/head gasket need doing.