2strokemoto Posted October 1, 2016 Share Posted October 1, 2016 hi all new to the forum been reading some posts love the site diving straight into it so my dad recently picked up a none runner yamaha dt 125 lc ypvs 1hr 1987 semi clean needs tlc but other wise good long story short i got it runing pretty quickly it wasnt getting spark so i cleaned up the grounds to the frame from the coil and a few connectors and she fired straight up, she didnt like to idle verywell adjustments to the carb seemingly did nothing to effect running conditions when i took her out she flew ran sweet through all the geqrs powervalve working ect but over the past few days starting her has been a bitch even bumping her off wouldnt work very temprimental as sometimes she dpes bump but its short lived and she dies symptoms hard to start and only idles for a couple seconds if that when she does before dying the odd back fire while trying to start when i try to bump her she spits n jumps on low revs but doesnt take if i hold the throttle back and kick her off she revs out and dies quickly i have tride everything i can to resolve this problem such as new battery new plugs b8es/b9es cleaned up the coil trimmed it back shes gettin a really good spark cleaned up all connections cleaned out the reed valve sonic cleaned the carb - mikuni vm26 ss 34x10 replaced most Orings in the carb replaced the air filter compression is good new clean tank new fuel new gaskets on the reed block shes getting good spark fuel and air after ive tried kicking her off a few times the plug is abit wet and black so i altered the float hieght a little bit to make sure she wastn flooding the only other thing i could thing that it is could be the timing but im a serious novice in that department, the bikes fab to ride but quickly becoming a headache ive already blow about 90 quid on bits trying to solve the problem. hoping someone on here could give me some better insight into the timing on these machines as the info for these old bikes is scarce at best unless my googles not working ha last note and maybe a thought could the backfires have blown a seal and its sucking in air from one ? could that cause the bike not to start? i can try and get a video tomorrow so you can see the problem your self. thanks in advance for any help what so ever Josh Link to comment Share on other sites More sharing options...
Moderator Cynic Posted October 2, 2016 Moderator Share Posted October 2, 2016 Timing doesent come and go. If she flew a few days ago its NOT timing. It cannot drift like a 4stroke with all the extra crap envolved. If it goes its gone. Bike stops. Bad idle jet/choke is what i would be rechecking and also look up the pipe to the cyl. My tdr was doing this when the rings pinged the powervalve. Still ran but poor starting. Could also be a crank seal (spray wd40 behind the mag and see if things change) but lets start easy. Link to comment Share on other sites More sharing options...
2strokemoto Posted October 2, 2016 Author Share Posted October 2, 2016 hi there thanks for your quick reply, i was thinking choke as she was starting with choke in or out choke out she wouldnt idle properly but would run but choke in she would idle at 3/4k revs if you let it drop below tht she would die, she was liking the choke out just a little bit to be honest, th left side seal has let some oil out i think that was caused by all the backfiring, if i clean all the fly wheel side out an she fires up and runs then it stays clean if she pops n runts n backfire then i get a little bit of oil popping through that side of the engine ofcourse that tells me the seals slightly bad/gone, choke could probably due to be replaced if im honest, when i took the exhaust off and slowly cranked the engine i could see a few small air bubbles when the rings met were the top of the vale is, tired rings ? damaged valve?, again thank you for such a quick reply this has deffinatley confirmed a few thoughts any other suggestions? thanks again josh Link to comment Share on other sites More sharing options...
Moderator Cynic Posted October 2, 2016 Moderator Share Posted October 2, 2016 2stroke rings are not as effective as a 4 stroke. If their in place their good enough to run ok. Your talking about being down on power not bad running. If the crank seal is leaking you need to fix it. Pointless doing anything else. Bad starting and subsequent seizure of the engine is guaranteed. Link to comment Share on other sites More sharing options...
2strokemoto Posted October 2, 2016 Author Share Posted October 2, 2016 no it was proving hard to start and didnt want to idle i just chnged the hieght of the floats put in a bigger float needle housing and jet and she started straight away your deffo right tho the choke is knackard and that seal is getting changed regardless, still needs a few tweak to sit an run right but so gla its actually working. thanks alot for your input bud josh Link to comment Share on other sites More sharing options...
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