dt125 problems

[metalskin]

started having probs with my bike the other day, cant figure out what it is.

first sign of probs was when i was sitting at some lights and it stalled, wouldnt start
up straight away, took about 10 kicks. then the throttle was sort of light feeling,
like it was running really lean, had to work the throttle a bit to get me another 100m to home.

went to start it a couple of days ago, and it wouldnt run right, hard to start,
would respond ok for a few seconds, then becomes unresponsive, if i hold it at say 3000rpm
it runs fine for 2 sec then starts to lean out and slowly work its way up to about 3500rpm
then it will cut out, if i do that even if i work the throttle a bit it will still stall.
riding it like that, goes ok till about 3000rpm then feels like its leaning out and sounds like the
choke is still on. other signs of something bad, it warms up to hot in about 30 - 40sec.


its had that many probs already i've checked everything, and checked again. cleaned the
carby 3 times, checked for air leaks, still has compression but suffering from reasonably bad blow by,
changed the plug, checked fuel lines, i even got the pinhole in m exhaust patched up..

and if anything, patching the exhaust has made it worse. i cant figure out what it is. any help appreciated.
                                                                                                cheers, Metalskin.

[DR]

exhaust pipe isn't blocked is it?

[metalskin]

exhaust pipe isn't blocked is it?

i wouldnt think so, was patched up in one place and a pinhole tacked over in another.
possibly the bit thats been filled could have a bit of material behind it but i wouldnt think
enough to make it run like it does.

[DR]

been through most of this before Metalskin I realize. Obvious things, too low on compression (when it warms up it's only going to be worse) starving for fuel (blocked fuel line, in tank strainer or fuel tap filter or possibly a kinked/pinched fuel hose) blocked vent pipes/hoses on carb causing a vacuum inside the bowl. Left crank seal leaking (liberally apply some grease around the seal, start the bike and see if it's any better for the short term before going back to it's bad habit) What gets me is you say when the exhaust holes were patched it got worse, it sounds like the choke is on and it heats up very fast. That to me is a sign the exhaust 'might' be blocked. Does the exhaust gas come out in nice puffs or does it just dribble out like a smoking gun? Without seeing the bike it is really hard to say unfortunately

[metalskin]

been through most of this before Metalskin I realize. Obvious things, too low on compression (when it warms up it's only going to be worse) starving for fuel (blocked fuel line, in tank strainer or fuel tap filter or possibly a kinked/pinched fuel hose) blocked vent pipes/hoses on carb causing a vacuum inside the bowl. Left crank seal leaking (liberally apply some grease around the seal, start the bike and see if it's any better for the short term before going back to it's bad habit) What gets me is you say when the exhaust holes were patched it got worse, it sounds like the choke is on and it heats up very fast. That to me is a sign the exhaust 'might' be blocked. Does the exhaust gas come out in nice puffs or does it just dribble out like a smoking gun? Without seeing the bike it is really hard to say unfortunately

i've double checked everything thats caused probs in the past and anything else i can think of.
smoke comes out as it should, but it was starting to run like that before the pipe was fixed. it does seem like a carb vent prob,
but it isnt. i reckon i will loosen off the pipe to see if its blocked or not tommorow. but im pretty sure it was like that before i fixed it,
just not for very long. i was going to get a rebore so i can put my new piston and rings in but now i want to sort this out
before i do anything else. unless thats my prob.. but it just sounds like it cant get enough fuel, or sometimes any.

[metalskin]

think i found it, this time the problem seems to be water in the muffler. took the muffler off and it spat out some emulsified oil/water
for a bit, took it for a quick ride without the can and it cleared up. i have no idea how it got there, i never left it out in the rain or anything 

                    cheers, metalskin.

[DR]

  I've found kids are good like that..see a hole so they feel it's their duty to poke the hose in it hope it's sorted regardless..cheers

[metalskin]

it seems im back to my original problem now the mufflers fixed.

ran ok for about 5min, got me about 3k's down the road and it started to sound like its getting no fuel again,

so i stopped for a few min, kicked it over and it got me about 100 meters.. kicked it 20 times, no chance of starting.
had a shifter handy just incase that happened, so pulled off the muffler and it fired straight up first kick.

it does seem to be pinging a bit, both with and without the muffler.
im guessing it could be the muffler still, somehow stopping the fresh mixture from circulating properly?
the only other thing i can think that is contributing to it, would be the blow-by in the top end.. any help/ideas appreciated.

[monaro308]

Not that it will help you,but my PE175 did kinda the same thing back in the 80's,a real slug that got worse.I cut the muffler end off and the packing was solid and soaked.
Repacked it and refitted the end and it was a new bike again.
Don't dismiss the clogged muffler as it does make a big difference as i found out.
Cheers....mario

[tony27]

Wouldn't the DT have a mechanical baffle? Try cleaning it out, possibly you need to set fire to the baffle to burn off some of the carbon

[metalskin]

Wouldn't the DT have a mechanical baffle? Try cleaning it out, possibly you need to set fire to the baffle to burn off some of the carbon

im pretty sure it doesnt have any packing of any sort. what would be a safe way of burning off the carbon?
would it be ok to clean it with kero and just burn off the excess?  cheers, metalskin.

[tony27]

Oxy-acetylene plant works just not set at a welding setting, very soft flame. Or at a pinch just chuck it in a fire.
By mechanical baffle I mean there should be a piece held in the muffler by screws at the back which is removable, thats the piece you're looking for. Take it out & look to see if there's any partly blocked holes then try running the bike for a short time to see if there is any difference

[DR]

be interesting to see what sort of compression you have Metalskin as this could also be the big issue, especially when it warms up. Without a first hand look I'm only guessing and using a hit/miss method.

[rocketfrog]

A blocked exhaust will definitely affect the way revs build and power output, the case in point in my experience was due to mud wasp in a brushcutter exhaust and on another occassion carbon blockage in the exhaust port and header of a Honda QR 50.
In both instances, clearing the blockage with a pointed tool and scrub with scotchbrite remedied the problems lickety split.
Also check the Fuel cap breather vent for blockage, once again the humble Mud Dauber Wasp can be a show stopper.

Cranks seals are also an often overlooked culprit of tuning problems, as Doc has mentioned a liberal coating of grease can aid temporary sealing to troubleshoot this problem.

Alternatively, you could pressurise the crank case and observe bleed the down rate or use soapy water to detect leakage at the seals and split line. This involves careful sealing of the intake and exhaust ports and using a modified sparkplug shell with a "T" piece brazed into the top to adapt a gauge and valve.

However frustrating this can be, don't give up mate. You will achieve a great deal of satisfaction when the problem is solved.

BTW, is timing an issue? too much advance will cause overheating and pinging, poor performance and ultimately catastrophic destruction of your engine. Consider starting with an overview of the ignition system static timing marks and put the word out for a loan of a known serviceable CDI unit to aid troubleshooting this system. I am sure that an appropriate quantity of beer would appeal the good nature of other DT owners!