Carbs

[19Feelgood80]

Have a 1980 XS 650 that I'm trying to bring back to life.When the bike is idling, engine still cold, throttle can be increased and immediately will return to idle. However, once the engine warms up, if the throttle is increased the engine speed increases, stays at that speed and will not return to idle unless the engine is turned off and restarted. Not terribly safe to ride this way. Throttle itself is not sticking; throttle cable has been replaced and not binding; carbs professionally rebuilt. Looking for help and suggestions. Thanks.

 

[funky]

Hi and welcome .....Sounds like mixture if all other setting are correct cam chain,valve lap, timming 15 degrees TDC,, float levels are correct. No intake or exhaust leaks ...you can also check the ATU (Advance timing unit) Located right side top of engine when sitting on it ...under chrome cover with 2x screws....make sure it has not lost a spring or has worn springs that are not returning the counter weights.. sticky throttle cable or grip. It a process of illimination.
It can be a multitude of issues or a combination or them or just one components failing, make sure your carbs are clean with clean fuel all jets are clean and as mensioned float levels correct.
All the best

 

[joebgd]

I think the 1980 and newer don't have any ignition parts under the above mentioned cover where the atu is.
80 on up is crank timed and triggered electronic ignition.
Check intake for leaks, maybe crab holders could be sucking air in.