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non-starting dt125

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hey guys,

I've been trying to diagnose why my DT125 LC Mk3 has suddenly stopped working after it was left for a few months over the winter. The engine doesn't start at all and therefore, as far as a beginner like me understands, it's either a problem with the spark, or with the mix coming into the engine. So, I tried to see if the plug sparked whilst outside of the engine, and as far as I could tell it didn't. After playing around with the multimeter, I decided to replace the ignition coils, and the spark plug. Seemingly, still no spark.

At the same time, I'd been advised that maybe the jets in the carb had become blocked, so leaving the electrics for a while, I checked the jets, and sure enough, the pilot jet seemed blocked, so I cleaned it. Still no joy with the engine.

Going back to the electrics, I rechecked the spark plug, this time using a wire to make sure the plug was properly grounded (I'd been worried that this wasn't the case before). This time, there was a definite electrical cracking sound (it is possible that this was there all along, and that I just hadn't noticed it) when kick-starting, although the spark still wasn't visible. In any case, the engine still wasn't firing.

So, that's the state of play, and as I'm pretty new to this, I don't really know what to do next. I'd be massively grateful for any advice.

Oh, and here are some random thoughts/questions that I've got:

- Could it be a weak spark? If the spark was right, would I be able to see it outside the engine as well as hear it? Is there any easy way (i.e. without specialised equipment) to check the strength of the spark?

- I'm assuming that if the timing was off, then the engine would at least mis-fire or something?

- Could I have messed something up with the carb whilst cleaning it? I'm pretty sure everything went back exactly as, but if the carb is really sensitive to changes (as some people have suggested), is it possible I've made things worse?

- Does the initial spark for a DT125 LC Mk3 come from the flywheel, or straight from the battery? (or maybe a combination of both?)

- Could the CDI unit have become damaged over winter? Could this cause a weak spark?

Sorry for the long post.

Cheers!!!

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hey guys,

I've been trying to diagnose why my DT125 LC Mk3 has suddenly stopped working after it was left for a few months over the winter. The engine doesn't start at all and therefore, as far as a beginner like me understands, it's either a problem with the spark, or with the mix coming into the engine. So, I tried to see if the plug sparked whilst outside of the engine, and as far as I could tell it didn't. After playing around with the multimeter, I decided to replace the ignition coils, and the spark plug. Seemingly, still no spark.

At the same time, I'd been advised that maybe the jets in the carb had become blocked, so leaving the electrics for a while, I checked the jets, and sure enough, the pilot jet seemed blocked, so I cleaned it. Still no joy with the engine.

Going back to the electrics, I rechecked the spark plug, this time using a wire to make sure the plug was properly grounded (I'd been worried that this wasn't the case before). This time, there was a definite electrical cracking sound (it is possible that this was there all along, and that I just hadn't noticed it) when kick-starting, although the spark still wasn't visible. In any case, the engine still wasn't firing.

So, that's the state of play, and as I'm pretty new to this, I don't really know what to do next. I'd be massively grateful for any advice.

Oh, and here are some random thoughts/questions that I've got:

- Could it be a weak spark? If the spark was right, would I be able to see it outside the engine as well as hear it? Is there any easy way (i.e. without specialised equipment) to check the strength of the spark?

- I'm assuming that if the timing was off, then the engine would at least mis-fire or something?

- Could I have messed something up with the carb whilst cleaning it? I'm pretty sure everything went back exactly as, but if the carb is really sensitive to changes (as some people have suggested), is it possible I've made things worse?

- Does the initial spark for a DT125 LC Mk3 come from the flywheel, or straight from the battery? (or maybe a combination of both?)

- Could the CDI unit have become damaged over winter? Could this cause a weak spark?

Sorry for the long post.

Cheers!!!

Hi,

if its a weak spark, the colour of the spark will be yellow. If your heart is strong try putting your hand on the spark plug as you turn it over; if you get zapped then its sparking. If not , try replacing the supressor cap . cheers

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Hi,

if its a weak spark, the colour of the spark will be yellow. If your heart is strong try putting your hand on the spark plug as you turn it over; if you get zapped then its sparking. If not , try replacing the supressor cap . cheers

:lol::lol::lol:

Do a video of it for the forum.

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You might need to change the fuel if it's been sitting for a while and clean out the old fuel. The fuel can evaporate leaving the oil to block things up and it might also take on some moisture. If you had blocked jets that could be part of the problem and depends on where and how the bike is stored. If it was running OK before the timing should be OK to at least get it started as you've got a new plug etc.

Hope that helps,

Gordo

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errrr.... hey, jebb - i might give that idea a miss if that's ok with you. I realise the current is low, but I still don't like the idea of 40,000V running through my body. Of course, if you wanna come lend a hand. :)

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errrr.... hey, jebb - i might give that idea a miss if that's ok with you. I realise the current is low, but I still don't like the idea of 40,000V running through my body. Of course, if you wanna come lend a hand. :)

Gladly, but I will need some lager first.

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i'll buy you a pint jebb, dont forget the video mate :D

ok, as awesomely funny as this has become, does anyone have any advice that doesn't involve me getting zapped? :P

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OK yes you should see a spark from the plug but the plug needs a good ground connection.

Taka a car jump lead and place the plug body in one jaw and the other end of the jump lead get a grip of the battery neg terminal or a clean bolt to the frame somewhere.

Have you got a haynes manual for this DTLC?

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OK yes you should see a spark from the plug but the plug needs a good ground connection.

Taka a car jump lead and place the plug body in one jaw and the other end of the jump lead get a grip of the battery neg terminal or a clean bolt to the frame somewhere.

Have you got a haynes manual for this DTLC?

hey,

yeah, we used a multimeter lead with croc clips to make sure it was grounded, and that's when we first noticed the cracking noise, although definitely can't see much (although it was an insanely bright day so maybe that was a factor).

yeah, i've got a haynes manual.

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so this multimeter lead, did it have a good hold of the plug, because I know these leads and the croc clips are small. anyway its dark now and perhaps you shaded the plug from the brightness of the sun

Again...do you have a spark?

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so this multimeter lead, did it have a good hold of the plug, because I know these leads and the croc clips are small. anyway its dark now and perhaps you shaded the plug from the brightness of the sun

Again...do you have a spark?

yeah, I checked late last night, and the spark seemed stong and decent enough (although I don't really have a basis of comparison). any ideas?

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Get someone to give you some help bump starting it, got any hills nearby?...Ohh you are using the choke arent you?

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A few random thoughts:

So your spark is good - you've got good compression? Thumb over the plug 'ole when kicking will give you an idea, drop a teaspoon of 2T oil down the plug 'ole and try again - if the compression improves you could have sticky rings - a squirt of WD40 down the plug 'ole may improve matters in that case, or it's a top end strip.

Modern unleaded is shite - leave it sitting for a while and it turns to cat's piss. Some engines don't care, but others (generally the more highly-strung ones) just can't use it. So, empty the fuel into your lawnmower (unless it's electric, which would be A Bad Thing), drain the piss out of the carb and then get a gallon of fresh stuff into the tank and carb.

Choke on, ignition off, one kick to prime it. Ignition on, choke on, kick & pray.

Still not running? Air intake boot off the carb, drop float bowl, squirt carb cleaner into and through the carb. Pour a bit of Redex carb cleaner into the float bowl before putting it back together, then try a restart. If it goes the Redex will give you a smoke screen to hide a WWII battleship, so don't do it if the neighbours have their washing out on the line! (Unless you hate them in which case give it the full Dr Evil maniacal laugh)

If it still won't go then you're looking at a proper carb clean - know anyone with an ultrasonic bath big enough for your carb?

HTH

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A few random thoughts:

So your spark is good - you've got good compression? Thumb over the plug 'ole when kicking will give you an idea, drop a teaspoon of 2T oil down the plug 'ole and try again - if the compression improves you could have sticky rings - a squirt of WD40 down the plug 'ole may improve matters in that case, or it's a top end strip.

Modern unleaded is shite - leave it sitting for a while and it turns to cat's piss. Some engines don't care, but others (generally the more highly-strung ones) just can't use it. So, empty the fuel into your lawnmower (unless it's electric, which would be A Bad Thing), drain the piss out of the carb and then get a gallon of fresh stuff into the tank and carb.

Choke on, ignition off, one kick to prime it. Ignition on, choke on, kick & pray.

Still not running? Air intake boot off the carb, drop float bowl, squirt carb cleaner into and through the carb. Pour a bit of Redex carb cleaner into the float bowl before putting it back together, then try a restart. If it goes the Redex will give you a smoke screen to hide a WWII battleship, so don't do it if the neighbours have their washing out on the line! (Unless you hate them in which case give it the full Dr Evil maniacal laugh)

If it still won't go then you're looking at a proper carb clean - know anyone with an ultrasonic bath big enough for your carb?

HTH

ok, so I checked the compression - as far as I could tell, it was the same before and after i added the oil.

then I swapped out the old petrol for new, and the thing still won't run. Is it now just a case of giving the carb another clean?

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Does it fire at all? any banging, spluttering, half hearted running....anything? :unsure:

nope - not a thing. no banging, no spluttering, no half-hearted running. there's not even a hint of some sort of ignition.

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ok, so I checked the compression - as far as I could tell, it was the same before and after i added the oil.

then I swapped out the old petrol for new, and the thing still won't run. Is it now just a case of giving the carb another clean?

1: Have you tried bump starteing it yet?

2: You have a good spark so all you need is compression and fuel

3: You changed the fuel so thats good but is the plug getting wet with unsuccessful attempts to start?

3: You say you checked compression, soo what did you find or is it a secret :rolleyes:

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1: Have you tried bump starteing it yet?

2: You have a good spark so all you need is compression and fuel

3: You changed the fuel so thats good but is the plug getting wet with unsuccessful attempts to start?

3: You say you checked compression, soo what did you find or is it a secret :rolleyes:

I haven't tried a bump start - will this work even though the engine isn't igniting at all?

I'll check to see if the plug is getting wet.

As for the compression, I did what KirriePete suggested. I took the plug out, put my hand over the hole and kicked it a few times. I then added some oil, and did the same. As far as I could tell, nothing changed. Is there any other way of checking the compression?

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I haven't tried a bump start - will this work even though the engine isn't igniting at all?

I dunno but its always worth a try read this Here

I'll check to see if the plug is getting wet.

If it isnt you wont get it started, I expect it is

As for the compression, I did what KirriePete suggested. I took the plug out, put my hand over the hole and kicked it a few times. I then added some oil, and did the same. As far as I could tell, nothing changed. Is there any other way of checking the compression?

well that will tell you there is some compression, you could hardly tell the difference by putting oil in by that method though :rolleyes:

Best way is a compression tester, a bit difficult with these bikes though (not much room)

Compression3MBHead.jpg

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