Please Help Me Yamaha DT 125cc Engine Dies

jasonDT · Two Stroke Sniffer Joined: 22 Feb 2011 Karma :

Hi Folks
Can any body help me i have a Yamaha dt 125cc LC 1986 when i bought it the headgasket was blown so i mended that the bike has had a rebore in its time to but ive put it back to a straight 125cc.
Here goses it starts up fine hot or cold but when i take it out for a run and open it up it goses well then all of a sudden it dies and splutters then i pull choke out then it will start again and run ok then it will do it again so on petrol is getting through ok ive cleaned carb out so thats ok when i pull the throttle back its goses great then just dies on me it will always start again afterwards with a few kicks it ticks over ok but sometimes dies to now ive also notice a noise a tapping somewhere in the head is this normal its a tick tick tick tick and quite loud to ive tryed everything i no to try and fix this but still no joy i would be so greatfull if some one out there to give me some advice ive just got it through its mot then this happends
kind regards jay
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hi to all and thanks for your help

Sam_Y_93 · World Chat Champion Joined: 04 Nov 2009 Karma :

Could be running poorly due to too much fuel? have you checked that they are the correct jets in the carb?

As to the tapping noise, have you checked the valve gaps?
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jemdna · Nova Slayer Joined: 27 Oct 2010 Karma :

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jasonDT · Two Stroke Sniffer Joined: 22 Feb 2011 Karma :

Avora · Renault 5 Driver Joined: 08 Feb 2009 Karma :

2 strokes dont have valves. Sounds like you've siezed it, and the piston is worn. Meaning piston slap is occuring. Happened on my damn hateful TGB. Needs to be stripped down again most likely. Shouldnt be an issue for now.
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jasonDT · Two Stroke Sniffer Joined: 22 Feb 2011 Karma :

jasonDT · Two Stroke Sniffer Joined: 22 Feb 2011 Karma :

prawny1 · World Chat Champion Joined: 28 Jun 2005 Karma :

You may want to check if the oil pump is working as it does sound like you are siezing up then freeing off as it cools down.

Do you get smoke from the bike?

When you say you put the bike back to 125 do you mean you had the barrel resleeved or did you just put a standard sized piston in the bike?
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hellkat wrote:

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jasonDT · Two Stroke Sniffer Joined: 22 Feb 2011 Karma :

P. · Red Rocket Joined: 14 Feb 2008 Karma :

Did you buy a new barrel and piston/rings/bearings etc.

What colour is the spark plug?

jasonDT · Two Stroke Sniffer Joined: 22 Feb 2011 Karma :

P. · Red Rocket Joined: 14 Feb 2008 Karma :

Not being A1 and attempting this may not be a great idea Laughing

Did you swap the carb over too?
Being that the older one was bored out... they probably would have changed the jetting.
I'd try the other carb on there... what about the exhaust.. are they the same.

It matters far more so on a 2 stroke than a 4 stroke Thumbs Up

Spark plug colour??

jasonDT · Two Stroke Sniffer Joined: 22 Feb 2011 Karma :

[quote="##Paddy##"]Not being A1 and attempting this may not be a great idea Laughing

Did you swap the carb over too?
Being that the older one was bored out... they probably would have changed the jetting.
I'd try the other carb on there... what about the exhaust.. are they the same.

It matters far more so on a 2 stroke than a 4 stroke Thumbs Up

Spark plug colour??[/quote
this has happend on both heads so i dont think it could be the carb as it wouldnt of done the same thing on the bore kit head the spark plug is a bit black i wish i didnt take this on now but a lovely bike
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hi to all and thanks for your help

jasonDT · Two Stroke Sniffer Joined: 22 Feb 2011 Karma :

theres a little fuel in the air box to is this normal
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hi to all and thanks for your help

Sam_Y_93 · World Chat Champion Joined: 04 Nov 2009 Karma :

Avora · Renault 5 Driver Joined: 08 Feb 2009 Karma :

If you've had a partial sieze, either from lack of oil, or riding hard from cold, then the piston will have worn away quickly, the rings maybe still sealing enough to start up again. If thats whats happened then you need to strip it down. I assume that you mean the engine doesnt bog down due to carb issues. Would look at that first. But easiest option which as a 2 stroke owner is check the colour of the plug. Never assume anything I suppose with a 2T because an air leak can cause a big problem and a simple spark plug can do very odd things.
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jasonDT · Two Stroke Sniffer Joined: 22 Feb 2011 Karma :

prawny1 · World Chat Champion Joined: 28 Jun 2005 Karma :

If you have water in your oil then your water pump seal has gone or the crankcase has filled with water and leaked through a bad crankshaft seal.

The gearbox and main crankcases are seperate on a two stroke so head gasket failure won't directly emulsify oil like in a four stroke.

If the crankseals are bad that can cause running issues since the engine looses initial/crankcase compresion and can even effect the reed valve operation.

you can pop your barrel back off and fill the crankcase with petrol or light oil and see if the level drops rapidly, if it does then you have bad crank seals or a bad main crankcase gasket(gasket is highly unlikely unless fitted incorrectly)

If your are worried about taking of the sump plug you can take off the clutch cover and empty it out by leaning the bike over, that would give you a chance to check the waterpump and gears too
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hellkat wrote:

Some people are only alive cos its against the law to kill them.

jasonDT · Two Stroke Sniffer Joined: 22 Feb 2011 Karma :

N cee thirty · Banned Joined: 31 Jan 2010 Karma :

get a haynes manual,will help you alot Thumbs Up

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jasonDT · Two Stroke Sniffer Joined: 22 Feb 2011 Karma :

P. · Red Rocket Joined: 14 Feb 2008 Karma :

prawny1 · World Chat Champion Joined: 28 Jun 2005 Karma :

you shouldn't get anything just falling out to be honest , but in any case you have a manual and would be abled to identify anything that did easily enough.
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hellkat wrote:

Some people are only alive cos its against the law to kill them.

Avora · Renault 5 Driver Joined: 08 Feb 2009 Karma :

The oil wont affect the running. To be honest, it shouldnt effect it like it is even if theres an air leak. Sounds like a strip it and rebuild job. In other words, buy another engine, and slot that in for easy up and running. Thinking

cant think of anything obviously wrong apart from the piston is slapping the cylinder. You might be lucky if you take the top end off. Have a looky see. Its the only way... Confused

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