[viennatech]

Re: Revs don't come down to normal on CB400T

I had this exact issue and didn't realize it was normal until I put some real hard thought into it.

First, get the bike running and warm, whatever way you need to make it get to where you are now (idles at 4k rpm when hot). At that point, hop off and turn your idle screw down till it idles at a nice 1250 RPMS. Now go ride it a bit and see if it settles at 1250 the way it should and rides smoothly. It should. If it doesn't then your problem may lie elsewhere. Ok now you're idle speed screw is set. It will NOT idle properly setup this way when dead cold, but it was not meant to run that way dead cold.

Now when you want to fire up the bike, you go full choke, it'll start and idle at 3000 or so. then as the bike warms up over the next few minutes, push the choke down to make it idle at about 2000 rpms. This will allow youto ride it easy until it gets warm at which time zero choke is required.

I believe that what happens is we set the idle speed with the idle screw when the engine is cold, as the engine warms up, the screw expands making the idle go up and up. Surprising what a small movement of that screw it takes to get a 4k idle. Since we generally are tuning the bike as it is cold from a repair, we don't realize that the idle set screw was not meant to keep a cold bike idling, that's what the choke's "high idle" is meant to do.