Posted August 25, 201311 yr 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
August 25, 201311 yr Moderator 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
August 25, 201311 yr That just about covers everything,,, post up pictures Tom,,, of the KE also, and a quick intro in the newbe section,,,
August 26, 201311 yr Author 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
August 26, 201311 yr Moderator 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
August 26, 201311 yr Author 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
August 26, 201311 yr Moderator 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
August 27, 201311 yr Author ... 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
August 27, 201311 yr Moderator yes i've got it now, like I said..try it without the filter foam fitted
August 27, 201311 yr 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 ...
October 20, 201311 yr Author 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
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