Here are photos missing pieces on bike or either replaced sloppy . Not sure if u can notice thru photos

For research on parts, this forum (the Search Forum function), CMSNL, Partzilla, ebay and the internet in general are good resources.

CMSNL and Partzilla are online stockists who show the exploded parts diagrams with the part numbers.

Personally, I look at CMSNL and ebay first. CMSNL often have photos of new parts and I use ebay to compare photos of what folks are selling to see if they are consistent with each other - sometimes they aren't and you have to have your wits about you!

If you select a part on either CMSNL or Partzilla, scroll down a little and you'll see which other models used that part.

Thanks for your time and help guys . Is there an after market exhaust system that will make it perform Better then the original one or should I keep the original and just jb weld it ? I saw some in 2015 mentioned fresco ?

You were pretty close it was throttle cable causing slide to stay wide open .

I'd keep an eye on eBay for the missing pieces and like what was said earlier you can find an exploded parts diagrams at Yamaha motor or any place that sells Yamaha parts. Sad to say there is no aftermarket exhaust for 77/78 dt250/400's. There may have in the past, dunno. But these have been gone for decades. Fresco could have just made the silencer for a 78 dt and not a pipe. People have been wanting a pipe for your bike just as long. I am hoping the 650 dollars for my pipe ( new silencer included) will come down if he (Gary) can be persuaded to make more of them. I don't know if he is interested in making a run of them. The best thing is for those interested to call. There is no demand without a phone call. Frank