4-5k RPM after bike warms up

Dear friends, please advise if you know what it can be or had problem like this.

Engine works fine at the start. When it warms up and i start riding within a minute RPM increase to 4-5k RPM and keeps that engine speed constant.
Things i did:

Clean carbs, replaced gaskets, took all apart and properly cleaned it.
Replaced exhaust rubber hoses
Took out cylinder head. had it machined
Replaced valve gaskets
Replaced cylinder head cover gasket and all the gaskets of the top part of the engine.
Cannot find a leak by spraying break cleaner.
Cables seem to be ok (from accelerator and chock)
Adjusted valves

Any ideas? weather is beautiful please help out, i really want to start riding

 

Yer bike is possessed. Sorry

 

try adjusting the idle knob when this happens. then you may have to adjust the throttle as well.it should have a little slack in it.
what are rubber exhaust hoses ?
what work was done to head?

did you sync carbs or just a bench sync?
where did you set mixture screws to?

 

I bought a this xj 650j 82 that has been sitting since 2009 without been driven. Cabs were clogged up. once i cleaned them and installed cabs back i got this problem. Oil was leaking out of everywhere hence i also took top part of the engine block and replaced all possible gaskets. oil does not leak now.

Only issue is the strange problem when its 1100 rpm on idle at the start when it warms up a bit, but once i start riding it within a minute it jumps to 4-5k rpm and does not want to go down unless i turn it off and wait until its cold again. checked valve clearance again today. and its perfect.
No oil leaks or air leaks (to the best of my knowledge, i sprayed everything and nothing seem to impact the throttle high idle.

I have not touched mixture screws and i did not sync the carbs. Also i did not touch throttle body adjustment screw because it seems to be ok when its cold.

I did check the throttle cable, it does not really have a slack by it closes properly. i will slacken it a bit but wouldnt it be a constant problem on cold and hot engine?
by hoses i meant the four hoses that connect carb to cylinder head. from my googling it appears number one place for an air leak so i had them replaced with all four new gaskets. Im running out of traditional options when dealing with high idle.
Guys know any good exorcist?

 

Much of the problems is here ^.

Gary H.

 

when it's cold and has a good idle, check if all the exhaust pipes are close to the same temperature (they burn your finger equally fast )
could be 3 cylinders idle at the right speed, the fourth one gets warm, comes to life and the idle zooms up

 

you can not set the idle until bike is warmed up
it has been my experiance that when you buy a neglected bike the po has set the idle high and tightened up the throttle cable just to keep it running.
if there is no slack in the throttle cable shaft will not go down enough to sit on idle knob when you back off on the knob.
if you can eliminate this as the problem we can start looking at other things.

did you do a rack break when you cleaned the carbs or just remove all the jets and diaphrams and clean?

 

Check to make sure the choke cable is not too tight. Try backing the idle adjustment screw out. Double check for vacuum leaks. Check the vacuum hose going to the petcock and make sure there is no raw gas going down that hose. If that is all good then pull the carbs back off and bench sync them & set your float levels wet.

 

I agree with polok and xj550H one of your carbs is opening fully when hot. If you have one or can get access to a manometer or the 4 vacuum gauge set up . Hooked up then you can adjust synch screws until you get an even reading...engine still might race you will also need to adjust idle knob. What you are looking for is an even reading accross all 4 carbs. This set up is not terribly expensive and is a good investment. Some make 2 bottle synch set up. Dont dispair the answers are on this forum

 

Follow the procedure for making one of these bikes idle and if all is good it'll run. Bench synch, wet set the fuel levels, set the mix screws at 2.5 turns out, and with good fuel, good spark, and no vac leaks she'll fire and stay lit. Then dial in the vac, tweak the mix and move on to the next item.

Gary H.

 

Thank you all so much for taking your time. I will try all suggested methods and will get back to you. I'm sure the answer might be simple, i'm just not experienced enough with this bike. This site is an amazing resource

 

Hi guys, sorry for wasting your time. I checked the exhaust pipes as advised by Polock, Cyl #3 pipe is stone cold and does not warm up. Explains the abnormal noise as well. Just as advised I did burn my fingers )). high rmp on cold and hot engine.
Checked electrical., took out plug, gives spark. Checked the resistance of Coils. Both are off measuring at 22 kohms instead of 11 on the sparkplug end and 2.5 ohms on the thin end but seemed to be working.
new spark plugs.
Took out carbs will take it all apart today and properly clean it. Maybe some garbage blocked the jet. As of now it seems that carb feeding cyl 3 fuel is blocked, air is still coming in hence creating internal air leak?
Spark plug was dry when I took it out.
I don't think its compression, but ill check that as well.

 

did you remove the spark plug caps (boots) off when you measured the coil plug wires?

never a waste of time its a learning curve for you and benifits others as well as we who offer opinions on what to look at.
Polock gave you a tool on how to check for a problem and isolate it to a cylinder.

 

I had a very similar experience, in my case the root of the problem was air leaking into the intake boots, between the carbs and the cylinder.
For me the leak was on the sealing surface between the boot and the cylinder, i fixed it by making some gaskets.
My compression, spark, and carbs were good, and after I installed the gaskets it was like a brand new bike.

 

I missed the part where you said that you had replaced the boots and gaskets, sorry about that, the symptoms that you are still experiencing seem to be exactly what I experienced.

Brake cleaner may not be a good indicating fluid for intake leaks, if you are using something similar to what I have, the major cleaning chemical is perchloroethylene which is an excellent degreaser but not a very combustible fluid. quick start, or an un-lit propane torch is a better substitute.

 

If the plug is dry, and you have spark but no fire, then the only cause is a lack of fuel getting through that carb.