Check the pulser on the stator plate there should be 90 OHMS resistance between the two connectors on it. I tried to recoil my pulser on a 75 DT400 which is the same exact pulser as yours and I got it to run but your bike sounds like mine did, the same thing it would idle but give it some throttle and it would sputter and run horrible. Possibly your pulser coils (yes there are actually two coils in that little plastic thing and they are connected to each other)are shorted and giving a messed up signal to the CDI which then may throw off your timing. If that is ok it is possible your CDI box is malfunctioning. I forgot, possibly the source coil located on the stator plate could have a short in it also throwing off the signal to the CDI. Check your service manual for the correct ohms on that coil. Check the ignition coil secondary and primary resistance. I bought a used ignition coil off of ebay and I used it for 1 mile and when I went to start it again the next day NO SPARK. The ignition coil must have been ready to go. I ended up getting a NEW one from Yamaha and that was expensive like $75.00