yamahamike Posted May 10, 2014 Share Posted May 10, 2014 Hello there, I got this bike that runs, it just kicksback and backfires when you open it up. Starts and idles but spark plug gets sooty after just a few minutes of running.I adjusted the timing a little bit forward then backward, it didnt seem to help. Anybody have any ideas? Thanks Link to comment Share on other sites More sharing options...
Moderator Cynic Posted May 11, 2014 Moderator Share Posted May 11, 2014 Why mess with the timing? Air filter? air leaks on intake? exhaust leaks? carb settings? changed plug/cap? checked electrical connections in ig? There are plenty more. If a dt400 starts and idles ok the timing is rarely out. Link to comment Share on other sites More sharing options...
slice Posted May 11, 2014 Share Posted May 11, 2014 If the plug is black then I would say it's running to rich so you need to adjust the fuel flow through the carb. Link to comment Share on other sites More sharing options...
blackhat250 Posted May 12, 2014 Share Posted May 12, 2014 Yip the backfire is excess fuel, Pull the carb,, check its jetted to manual spec,,Carb-mikuni VM34. Mainjet 190 -pilot-80. check the reeds too , there old now ,,pull the reed block and inspect, Link to comment Share on other sites More sharing options...
yamahamike Posted May 16, 2014 Author Share Posted May 16, 2014 Ok thanks everybody, I will keep you posted Link to comment Share on other sites More sharing options...
yamahamike Posted May 22, 2014 Author Share Posted May 22, 2014 I pulled the reed block, looks like there hanging open just a bit, around .020 is that excessive? Would that be making it pop? And have a dead spot about 1/4 to 1/2 way open? The main jet is 160 and the pilot is 40. Link to comment Share on other sites More sharing options...
Tommy10bikes Posted May 22, 2014 Share Posted May 22, 2014 Wood ruff key sheared. Link to comment Share on other sites More sharing options...
yamahamike Posted May 24, 2014 Author Share Posted May 24, 2014 No, it was, fixed that, that was the first thing I checked. The fin on the bigger coil that holds a couple wires is cracked. I jb welded that. Would that do anything negative? The wires are still soldered together and not touching metal. Link to comment Share on other sites More sharing options...
blackhat250 Posted June 21, 2014 Share Posted June 21, 2014 The main jet is 160 and the pilot is 40. Well" these are not standard,, , but should be lean,,,but yours is sooty, so somthin is wrong,,, chances is the P.Owner done this to sort the problem,, i would try another carb,,, to see, Link to comment Share on other sites More sharing options...
yamahamike Posted June 28, 2014 Author Share Posted June 28, 2014 Well" these are not standard,, , but should be lean,,,but yours is sooty, so somthin is wrong,,, chances is the P.Owner done this to sort the problem,, i would try another carb,,, to see, Link to comment Share on other sites More sharing options...
yamahamike Posted June 28, 2014 Author Share Posted June 28, 2014 Ok, but I have an old Yamaha manual that says those are the factory jets for a 1975 dt 400. I put a timing light on it and it seems to be firing 2" before the pulsar pickup. The mark on the magneto 2" before pulsar Link to comment Share on other sites More sharing options...
yamahamike Posted June 28, 2014 Author Share Posted June 28, 2014 Ok, but I have an old Yamaha manual that says those are the factory jets for a 1975 dt 400. I put a timing light on it and it seems to be firing 2" before the pulsar pickup. The mark on the magneto 2" before pulsar Link to comment Share on other sites More sharing options...
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