xj550 engine reves at 3000 after idling for 15-20 mins... to hot ?

hi all
new to aircooled engines,whilst working on the xj550 (checking for oil leak ) after 15
mins in garage the revs are slow to fall after blipping throttle then after another 5 mins blip the throttle and it sticks at 3000 revs i looked at thottle etc all good snaps shut fine and the carb side shut fine as well (cable slack) however if i press hard (and it must be hard) on the throttle rod (on top of any sync screw) there dosent feel like any movement but the revs drop back to 1700 (which is normal at the moment for it)
Ii this just because its getting to hot being stationary for so long and carb parts heating/expanding or possibly something else
cant check what its like whilst riding as not taxed/insured atm due to lots of work needing to be done on it
thx for any help

 

Idle adjust too far in?

 

Check your petcock. Maybe a vacuum leak there. I had similar issue on my 550.

 

thx guys idle adjust is ok ill have to check petcock cheers

 

I would guess the carbs are out of synch, one butterfly or more are holding other open.
Wrong mixture setting, or one or more almost clean carbs could affect.
Have your carbs been to "the church of clean"?

 

10 or 15 minutes is to long to run motor while standing still. put a couple of fans blowing on motor.+

throttle cable sounds like you have it adjusted properly.
choke completely off? push down on the plungers.
it takes about 10 to 15 miles to get motor properly warmed up to set idle.

could be carb to manifold boots have cracks or not tight to cylinder head. clamps not installed correctly.

vacuum leaks spray some carb cleaner at the throttle shaft seals see if the rpm rises you can also use propane do the same for the boots.
also check the airbox to carb boots for tight clamps and cracks.

if carbs were bench synced that should be good enough for idle returning to 1050 rpm I set mine at 1200 rpm to eliminate the chain slap sound of the 550

 

thx for help
the carbs were ultra sonic cleaned and rebuilt before i had it ,sync is good,mixture seems fine ,choke is adjusted correctly, manifold to carb boots appear cracked but tested and dont leak,set idle to around 1300 after getting warm as chain slap was quite noisy. Ive not checked the boots from carb to airbox yet but everything seems good tend to think its just way to hot, engine gets to where its starting to give off heat smoke so if i cant find anything ill carry on with other bits that need doing and see what its like when ridden thx again guys much appreciated

 

Check your choke system. I had a kink in my cable that would open the starter plungers a little even when the choke looked closed. Took me a week to figure it out. Petcock could be an issue, as could a stuck float or needle. Also make sure you don't have any holes or airgaps in your intake system, like a cracked boot.