Tom125mx Posted August 25, 2013 Share Posted August 25, 2013 Hi, I'm new here! I'm from switzerland and bought 2 seventies 2stroke offroad Bikes. The Yamaha makes some Trouble right from the beginnng.... When cold my mx 1978 dt 125 does not start well... it runs a few seconds at low revs only and then it dies... When I Open the throttle dürfend starting is even worse... So after dozends of trials it finally runs smooth. Starting warm ist not a Problem.. Carburator has been cleaned an checked. Fuel supply is fine. Could this be a problem with the ignition System as well? Any ideas? Thx in advance Tom Link to comment Share on other sites More sharing options...
Moderator Airhead Posted August 25, 2013 Moderator Share Posted August 25, 2013 i'd say its a carbrettor choke not working issue Two important points here 1: The bowl gasket needs to be in good unbroken condition around the fuel lift tube, see 'B' 2: there is a small hole right at the bottom of the fuel lift chamber so that fuel can pass into there from the bowl, see 'A' Hey we do appreciate an intro in 'New Members' section Link to comment Share on other sites More sharing options...
blackhat250 Posted August 25, 2013 Share Posted August 25, 2013 That just about covers everything,,, post up pictures Tom,,, of the KE also, and a quick intro in the newbe section,,, Link to comment Share on other sites More sharing options...
Tom125mx Posted August 26, 2013 Author Share Posted August 26, 2013 the choke-system as root cause sounds meaningful! but it's strange, because I just cleaned the carburator with compressed air and an ultrasonic bath ... I will dismantle it again and repeat the cleaning procedure ... any other idea? I keep you updated.. tom Link to comment Share on other sites More sharing options...
Moderator Airhead Posted August 26, 2013 Moderator Share Posted August 26, 2013 the choke-system as root cause sounds meaningful! but it's strange, because I just cleaned the carburator with compressed air and an ultrasonic bath ... I will dismantle it again and repeat the cleaning procedure ... any other idea? I keep you updated.. tom I'm not thinking it's anything else right now Tom, check that little hole is clear check the gasket check the brass tube is intact Link to comment Share on other sites More sharing options...
Tom125mx Posted August 26, 2013 Author Share Posted August 26, 2013 Ok. Hope i have some time next weekend... Just made a quick test in the garage: without choke it started! (Cold) -with Choke it died as described befördert.. Strange.. Cheers Tom Link to comment Share on other sites More sharing options...
Moderator Airhead Posted August 26, 2013 Moderator Share Posted August 26, 2013 maybe I misunderstood what you said in your opening post Tom, i thought it wouldnt start well and I naturally assumed you were using the choke. so it starts without choke but not with it Try taking out the air filter foam but replace the cover Link to comment Share on other sites More sharing options...
Tom125mx Posted August 27, 2013 Author Share Posted August 27, 2013 ... I tried to start with choke all the time.. which did not work as descibed in my first post. recently I tried to start without choke: with throttle closed it starts (when I open the throttle, or pull the choke it dies) when the motor runs for a few minutes (and gets warm) everything is fine... does this info help for a refined diagnosis? tom Link to comment Share on other sites More sharing options...
Moderator Airhead Posted August 27, 2013 Moderator Share Posted August 27, 2013 yes i've got it now, like I said..try it without the filter foam fitted Link to comment Share on other sites More sharing options...
blackhat250 Posted August 27, 2013 Share Posted August 27, 2013 Hi, I'm new here! I'm from switzerland and bought 2 seventies 2stroke offroad Bikes. The Yamaha makes some Trouble right from the beginnng.... When cold my mx 1978 dt 125 does not start well... it runs a few seconds at low revs only and then it dies... When I Open the throttle dürfend starting is even worse... So after dozends of trials it finally runs smooth. Starting warm ist not a Problem.. Carburator has been cleaned an checked. Fuel supply is fine. Could this be a problem with the ignition System as well? Any ideas? Thx in advance Tom No mention of choke atall tom,, / Get that pilot jet out ,, sounds blocked ... Link to comment Share on other sites More sharing options...
Tom125mx Posted October 20, 2013 Author Share Posted October 20, 2013 Just to close this discussion: ROOT CAUSE WAS THE BOWL GASKET, Repaired it and now it fires on the first kick!! Thx for your help! Tom Link to comment Share on other sites More sharing options...
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