rpms slow return

I have a 1978 XS400E all original. The problem is that when the engine is hot, it will not idle down unless i use the brake. I can be cruising along and take my hand off the throttle and it will stay at speed until I brake. Then the engine will slow down. And often waiting at a stoplight it...

Howdy! I just recently bought a 1980 Yamaha XS400 Special II, and need a bit of help with an issue that I can't for the life of me figure out. I am by no means a mechanic, just started rebuilding bikes as a hobby a few years back. These threads have been an absolute godsend in my rebuild...