I have a 1978 dr370 that just l a week ago was running perfectly, but I let my friend ride it and when he went full throttle he started getting crazy backfire/bog. I've messed with the flote level and cleaned the spark plug and it now wount evan run past an idle. I think It would be a broken valve spring but i dont want to take it apart if I'm not 100persent sure. Because I've had this bike have this problem before and I dont know what I did to fix it but it just started running right. Like an hour before my friend rode it the exaust bolt did come out resulting in the exaust falling off but I put it back on and it worked fine until my freind maxed the throttle in 5th gear.the bike has allways had a loud valve clicking noise evan when running mint. When I messed with the flote once it revved up past idle once then when I tried again it just bogged/misfired/died.
I love to ride and just cant stand it when something breaks and I cant figure out how to fix it.I'm really hoping for some input on what could be wrong with it and what I should do. I really only want to open the valve cover if others think that could be the problem. Thank you!