DT125R ARCHIVE

bagpuss · DTR Respected Member

bike starts when cold but not when hot?

Dingle001 · DTR Senior Member

Easiest thing to check first is the air filter. Try removing it then run the bike and see what happens. It sounds like it might be running rich making it difficult to start when hot.

bagpuss · DTR Respected Member

cheers for the reply. Ihave just arrived at my mates where the bike is but it wont start at all. there is a good spark and the plug has petrol on it. i am now thinking it could be electrial

El_Faggo · Forum idiot

+1 Dingle Running rich, the rich jetted carburettor is having same effect as the choke does when the bike is cold, not enough air and too much fuel, if it was electrical it would be random, what color is the spark plug when you take it out and do you normally have to use the choke to start it or does it start fine without it.

bagpuss · DTR Respected Member

the plug is dry but black and yes the choke does help to get it started. i am getting the odd backfire which tells me that the timeing is not quite right but the stator plate is not ajustable. reading through the manual things are pointing towards the cdi unit. cry

El_Faggo · Forum idiot

check this out. http://www.theultralightplace.com/sparkplugs.htm

bagpuss · DTR Respected Member

cheers the pictures are verry much the same in the manual. Ihave ordered a new cdi so i will let you know what happens.

I am not entirly sure that the carb is the right one for the bike, i have been told i should be using a 22-24mm, can any one shed some light on how a carb is measured, is it by the inlet, outlet or the size of the slide?

Dingle001 · DTR Senior Member

Early models were 26mm - Mikuni VM26. The venturi size should be stamped on the carb. Not the easiest thing to measure as the bore is tapered and its the smallest diameter measurement about where the needle is.

check out this to see if it looks the same:

http://www.allensperformance.co.uk/products-vm.html

Dingle001 · DTR Senior Member

Backfiring would suggest an ignition problem then. Have you changed the plug?

bagpuss · DTR Respected Member

yea i have tried several plugs, not alot more i can change now, if a new cdi dont sort it i will then look at a new carb and stator.

mr karnage · Guru

if its just started happening out of the blue then it could be a cdi problem, dont think it could be a stator problem otherwise it wouldnt be sparking

but it does sound alot like the jettings out, buy a few jets smaller and see if it makes a difference rather than buying a new carb

bagpuss · DTR Respected Member

i should be getting the cdi by next friday so will try that and if that dont work will have a look at the jetting.

fused420 · DTR Senior Member

Sounds like it could be oversize main jet to me, i had simular simptons develope when i was trying to set up the carb on my Aprilia. I found was that the bigger jets made the power valve feel wet, and the bike back fire. Where as smaller jets made it bog down pulling away, but the power valve was good. I don't know wether any of this is any use to you (or anyone!), but there you go..

bagpuss · DTR Respected Member

I WILL BE GETTING THE CDI UNIT TOMORROW AND SEE IF THAT MAKES A DIFFERENCE, my mate has been working on the bike and has found by turning the power valve to shut the exhaust port on the exhaust side instead of the piston side makes a big difference as to how the bike starts and runs. If the cdi does not make any difference i will be taking a closer look at nthe jets and will keep you posted. I would like to take this oppertunity to thank every one for there comments.

bagpuss · DTR Respected Member

The bike has a 200 main jet in at the moment, some feedback on what other people are using would be helpfull cheers.

bagpuss · DTR Respected Member

cdi still not turned up cry

bagpuss · DTR Respected Member

hi again just to up date i tried a smaller jet but the bike would not tic over without the choke being onso went back to the 200 jet, i have now changed the cdi unit and the bike is running smoother but still lacks top end power, i dont know why so any comments all welcome. cheers.

NEV · Guru

Am sure #210 is standard on the 28mm carb, no top end could be down to the fact your mate pinned the powervalve to closed,
check front and rear sprocket teeth too it could be that the sprockets are geared for quick off the start rather than top end, are you running aftermarket exhaust? such as a DEP, or big one? as you'll probably need to upjet for one.

bagpuss · DTR Respected Member

Hi the carb is 26mm and i have just bought a big one front pipe but not got round to fitting it as yet. Although the bike is running alot better there is still a splutter between 1/4 and 3/4 throttle but when on full throttle it clears i have been told that this is down to the main jet needle is this correct?

Dufferz · DTR Respected Member

Check the jet needle's clip position, as standard it is 2nd clip from the top (middle one)

bagpuss · DTR Respected Member

cheers for your comments the splutter has stopped but the dam thing still wont rev over 6/7000 rpm reaching a top speed of 45mph I AM CONVINCED THAT ITS NOT THE GEARING THATS WRONG ITS JUST THAT IT WONT REV i am at a total loss of what to do next so please keep your comments comming cheers.

GADGET · Guru

power valve ? 180 out ?

no power after 7 thou ?

even if you change the main jet if it cant use it then its no good

the backfire could be a broken or bent woodruff key

what do ya think fella's

ps :the pipe could still be restricted ????????? confuse

good luck dude

bagpuss · DTR Respected Member

The power valve is set so un restricted, i will be trying some bigger jets this week when they arrive, and i think the backfire was down to a crack in the exhaust as i have now fitted a new one and the backfire has stopped, and as far as i can see the woodruff key looks a ok. The bike is a mk 3 1987/88 and i have read about some wires behind the clocks that can restrict the enguin would this apply to my bike?

bagpuss · DTR Respected Member

Hi just an up date i removed the powervalve today and found that it was totally caked in crap so i took it out and polished it up almost like new and now the bike is reving a lot better . I also tried a bigger jet and that also seems to be helping i am now using a 210 instead of a200. smile

bagpuss · DTR Respected Member

This was the condition of my powervalve when i took it out covered in crap!!!

-- Edited by bagpuss on Sunday 15th of January 2012 06:11:07 PM