Posted May 10, 201410 yr 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
May 11, 201410 yr Moderator 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.
May 11, 201410 yr 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.
May 12, 201410 yr 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,
May 22, 201410 yr Author 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.
May 24, 201410 yr Author 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.
June 21, 201410 yr 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,
June 28, 201410 yr Author 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,
June 28, 201410 yr Author 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
June 28, 201410 yr Author 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
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