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DT125R Forum -> Tuning -> BACK PRESSURE (exhaust)
Post Info TOPIC: BACK PRESSURE (exhaust)
robby963


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BACK PRESSURE (exhaust)
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right my 2stroke 1999 yammy dtr 125 has no exhaust, does it need it to start, i hear you do due to backpressure, someone verify this please.

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R Hartley
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the engine will start without back pressure from exhaust but makes it more difficult to start and feckn loud when it does, using an exhaust definatly helps you start bike easier but wont stop it from starting wink.gif

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robby963


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oh its just my bike wont start with it at all, flames have came out twice thats it, any ideas ?

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craigbulmer


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hmmmmm odd.
i took my silencer off and rode around the village :D loud as feck :D slow tho lol

you changed any jets?

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Yamaha DT125R - 2003
robby963


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i dont know nothing about jets, instructions and i could do it.

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R Hartley
woll


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is it trying to fire or nothing at all?

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RudiRulez


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when mine was flaming and backfiring whilst trying to start it turned out to be the sparkplug was broken, as soon as i fitted a new one it started straight away.

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Jonpearson17


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craigbulmer wrote:

hmmmmm odd.
i took my silencer off and rode around the village :D loud as feck :D slow tho lol

you changed any jets?


Silencers on 2 Strokes dont make a Difference to the performance, Its the Expansion chamber that does all the back pressure.

 



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john sorry mate but your wrong, taking a rear silencer off a dtr can make you loose up to 20mph because of lack of back pressure

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robby963


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i replaced spark plug the other day, it wants to start but just doesnt, bumping it doesnt do much either


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R Hartley
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battery ok?

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woll


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gaz surely if he's bumping it he doesn't need much battery power if any. Is it getting fuel and sparking ok?

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Mark
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to bump a bike you dont need the battery at all m8, sorry my bad lol should read things better lol, try as woll says make sure you have fuel and spark, check the micro filter too on carb fuel inlet, also remove spark plug with ht cap on it, hold the spark plug over the hole on engine, crank the kickstart over a few time, watch your spark plug, if the spark trys to jump in the barrel its fine,if it dont then id check ht coil,alternater then cdi wink.gif

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robby963


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right sparks fine, petrol is deffinitely gettin through, previously cleaned carb, i cnt think anything other then the exhaust much be on, but it will take some time i need to tap out the holes for the exhaust, there ruined,

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R Hartley
woll


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Has it been wet recently? my bike did a similar thing a few weeks ago it has a spark but it wouldn't start and it turned out i had a damp ht lead

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robby963


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ahh right i have checked and double checked and nothing appears damp at all, i got a dry sheet and went over it to be positive, i just cant think what it could be at all, im thinking of gettin a new carb, any thoughts on which one may fit a 1999 dtr 125?

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R Hartley
woll


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try putting it on something warm for a few hours mine didnt seem damp but putting in on an argor for a few hours sorted it

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Mark
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all flatslide makuni dtr carbs will fit wink.gif

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woll


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If fuel is getting into the cylinder i fail to see how replacing the carb will help. have you done a compression test?

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Mark
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blocked main jet idle jet blocked or incorrect float height would do it woll

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robby963


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not a compression test no, i was looking at getting the tool to do it myself, tbh i think it actually could be the exhaust because it seems to want to go but doesnt have momentum to carry on, could the exhaust make a difference to gettin it started ?

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R Hartley
robby963


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could it be my electrics, all that is connected to the black box is the HT lead and magneto wires, can anyone write on here which wire goes where


example

white/red - black






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R Hartley
robby963


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robby963 wrote:

oh its just my bike wont start with it at all, flames have came out twice thats it, any ideas ?



sorry this was ment to say wont start without it at all,



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R Hartley
woll


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so gaz he doesn't realy need a new carb it just may need jets clearing and float setting right?
And all that goes into the igniton coil is the two wire cant remember which way round they go tho and the ht lead.
Can you make a vid of trying to start it may be easier to understand and diagnose if we can hear/see it


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Mark
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woll i didnt say he needed a new carb??????? robby said he needed a new carb and asked what ones fit, i answered what ones fit!!thats all

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woll


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i know you didnt sorry if it came across that i did i was just asking if he might need it cleaning and setting correctly. my bad mate

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its cool,yeh basically need cleaning and float height checked, id do it anyway then that area is covered wink.gif

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robby963


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how to i clean jets and level the float i dnt know how to do that

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R Hartley
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http://www.activeboard.com/forum.spark?aBID=66365&p=3&topicID=31622105

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that is a link to your jets, you will see them in pic one, blow the holes clean inside the jets, also might be an idea to download this mate wink.gif

http://dtr125.net/workshop-manualf.htm

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