Reading the Spark Plug Color
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First thanks for your replies ! Now it’s a DT 125 R 1997 , with mikuni flatside TM28SS. I bought it second hand , the piston was breaking apart ( small pieces had broken up and scored the cylinder but it was still running no problem ). Anyway I exchange the cylinder from a second Dt engine I have, the cylinder has 8000 km on it and just to be on the safe side I took it to a shop , they checked it out and gave me a new piston, rings , small bearing and Athena gaskets.
This is my try to tune the carb , after the top end rebuild ( I also followed the info from this side on how to do a top end rebuild and run-in ). The snorkel is in, but it’s not a tight fit with the air box.. ( I mean it has some play, it’s not like a solid piece of rubber ).
Regarding the oil pump, I checked it following the Haynes manual an I thinks it’s ok. ( I don’t have the specific tool for this so I measured some pieces of copper foil with the caliper and used that as a reference ).
The exhaust is stock with no obvious restriction. On more thing to consider regarding the oil is that I still run the one that the bike came with… Unknown age or brand…
The other setting of the carb are stock as the rest of the engine. It idles stable at 1.5k rpm and the revs drop according to the throttle position so I don’t think It’s leaking air ( at least not in a noticeable way ) . The rest of the engine and the bike has 38700 km on it .
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@panmil92 Did you have the cylinder honed? Its not enough to simply through in a setof rings a d a piston on a used bore. The piston rings need to seal on the cylinder walls.
Whilst I doubt thats your problem its worth checking.
Are you getting excessive smoke? That plug looks too oily. I winder if the cranjkshaft seal is starting to weep.
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@panmil92 WHOOPS!!! My bad I forgot to add the link. :grinning_face_with_smiling_eyes: :pouting_face: :confounded_face: :persevering_face: :smiling_face_with_open_mouth_closed_eyes: :winking_face:
See here; https://dt125r.co.uk/topic/1590/spark-plug-heat-range-advice
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@Calum I took the cylinder to a well known shop for doing honing/ reboring , etc ( in Greece ) , he actually checked the cylinder for clearances as well as condition ( for almost 40 mins ) and then he gave me the correct piston. So I guess ( hope ) that honing is not the issue. I wouldn’t say I get excessive smoke. It smokes in the beginning and under hard acceleration , no more than what I see on youtube with this bike..
About the crank seals I have no idea, I check the oil level when warm and it seems the same. Unfortunately with the university, the only period of the year I can do the bottom end is the next summer. ( I’ll probably do it anyway then cause the old one had a little surface rust on the counterweights and I want to replace the bearing as well , i just hope it doesn't give up in this year :smiling_face_with_halo: )
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QUESTION : Will a dead battery affect the performance of the bike at WOT ? .
On my way driving home, I noticed my horn was not working ( when a real gentleman driving an Audi decided to cut in my lane , as I was accelerating, with no flash/warning :face_with_steam_from_nose: ) and after I arrived home I checked the battery to find a dead cell. The max voltage of the battery under 0.5 Amp load was a steady 10,3v. No load voltage of 12.6v.
In the same day , before I noticed the battery issue, I replaced the main jet to the manual recommended 240 ( from the 190 I was running as a test) and the bike starts to bog the moment you pass the ¾ of the throttle.
So, will the dead battery make my bike feel over-rich as I go WOT or the two things are not connected ?
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@Calum Hmmm, I measured the voltages at both the charging and the lights outputs. They are exactly on specs. I have no other idea on how to check if the ignition pulses are correct ..
If it’s not the battery , then I’m looking again at the rich problem regarding the main jet.
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@Calum It will be my priority tomorrow. I’ll fit a new battery, test the response of the engine under all throttle positions and then if necessary I’ll lean the main jet . I will of course update the thread when I have more information :winking_face:
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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: )
