Reading the Spark Plug Color
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@panmil92 My 2003 dt 125 r runs exactly the same without the battery and nunning without a battery there is no way at all that it can effect the performance of the bike like @Calum said doesn't make any difference with no battery unless faulty electrics or generator etc. Without battery fitted and multimeter on battery wires when i rev the bike a little it says 15.8 volts
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@2stroketerry I have the same voltage reading without the battery, with battery fitted it drops a tiny bit to 15 V.
Since the problem only occurs at WOT , I’m leaning towards rich main jet , even though it’s a 240 as stated on manual .
I managed to charge the defective cell ( kind of, it holds 2.1v with a 2 amps load ), so I will run a test with the battery charged. If it still bogs at WOT, I will fit a 220 jet and re-test.
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@panmil92 The 1997 dt does not use a 240 main jet only the later models have a 240, the correct size main jet for a 1997 dt is a 210.
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@2stroketerry Oh , yes, I failed to mention that I run a mikuni TM28ss that was taken from a newer Dt. From the newer engine I took the cylinder ( with the YPVS and servo ), the carburetor and I installed them on my 1997 Dt.
Mine had scored the cylinder and somehow the previous owner managed to bend the air way of the carb, that be the reason i replaced them from the back-up engine i have.
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Btw, I was wandering why if the engine is the same they have different jets fitted on the same carburetor through the years ?
Or the engines are not so similar and I’ve made a huge mistake interchanging the cylinders
( although after 300k kilometers nothing exploded, even at 10k rpms :smiling_face_with_halo: ) -
@panmil92 Depends what cylinder the 1997 engine had on it as the earlier engines have different stroke crankshafts. If the early engine had a 3MB00 cylinder on it then would be fine as the late engines all run the 3MB00 cylinders, also the really late engines have the 3MB high compression head that gives more horsepower compared to the earlier 3BN head with completely different squishband.
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@2stroketerry If I remember correctly both cylinders had the same number and the same heads ( the 3BN type with the non-flat squishband ) . Now regarding the markings on the crankshaft cover I think they were a little different ( something like Y-1 , and Y-2 ? I’m not sure about this I need to call my brother to check as the donor engine is on a different town )
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I found a pic, the crankshaft cover on the 1997 bike reads ( 3BN03 )
----------------------------------------------------------------------------- ( Y-1 )and from the donor bike it reads ( 3BN03 )
--------------------------------------------(Y-2)
What the second code means anyway ? -
@panmil92 The number on the cover has nothing to do with engine types years or models as even the latest 4BL engines have 3BN03 Y-1 on the cover.
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@2stroketerry Ok , so how i know if the stroke of the cranksaft is the same in both engines. *** And on that note, if it was different what would happen ? With the exception of bogging at WOT the engine works OK ( i think.., keep in mind this is my first 2-stroke bike and my first bike overall
) .Also DAMN that's a squeeky clean engine you have there !
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UPDATE – First of all, yes a working battery gives the bike a lot more torque after 5-6k rpm, I think as well that the YPVS servo is not working correctly without a steady 12v source, or / and , the ignition is not working correctly ( thus the loss of torque ) .
Secondly, the 240 main jet was a disaster , it was like pulling the choke after ¾ of throttle , nevertheless I took a pic of the sparkplug after 15 secs at WOT :
Now I have fitted a 210 main jet. I run some tests and this is what the spark plug looks after 10 mins casual driving and then 15secs at WOT :
I noticed that now approaching 4/4 throttle I had some cuts that I think it was misfire ( it sounded like an interruption of the normal sound for a split second, it had a muffled note not metallic or pinging ). This may be due to the spark plug being fouled from the previous over-rich condition. Still, going from 3/4 to 4/4 seems like you are still holding ¾, there is no more ( or very little ) acceleration and the note of the engine gets a tiny bit more “ heavy”. It does not bog like it did with the 240.
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Another update ( kind of ). I was driving home at night , it was cold ( 15 C from 29 C in the midday ) and the bike had the most responsive throttle response I’ve seen :face_with_open_mouth: . It was like a rocket revving from idle till WOT with no problems at all. I guess it was the temperature ? One change i also made before the drive was i emptied the oil tank ( it was almost empty anyways ) and filled it with Motul 710 2T. I’ll make more observations in the following days…
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Current bikes:
DT125X '07
Street Triple R '11
Aprilia ETV1000 '02Previous:
DR650RSE '96
FJ1200 '92
