Desperate for help

Hi people. I have a yamaha XJ650 1983. Rus great. But after thorougly warmed up and opening the throttle a bit the RPMs hang at around 3k. A quick jerk of the throttle will bring it back down to 1050 and it idles perfectly at that rpm. after is even warmer a quick jerk to the throttle will not bring it down, only super rev it. Although I can always force the RPMS down when dowshifting (downshifting doesnt actually slow me down, i have to brake). It feels kinda of like a cruise control. I can let the throttle go and itll just keep going.

Ive checked the enrichment circuit and it closes fine.
the throttle cable does not bind
it does not have a vacuum leak
it does not need to have idle screw adjusted because it idles fine until i open throttle enough, but only when it is thoroughly warmed up

The only lead I have is that it's maybe the carburetor slides sticking? But I have no Idea because I'm not a mechanic nor a professional. But I do have the original yamaha service manuel to help me out and the basic tools to do most jobs.

Any help would be greatly appreciated.

The next link contains pics of my bike itself and of the carburetors just incase theres something specific about them I should know.

s655.photobucket.com/albums/uu273/weissmikael/


thank you!

 

I just recently set my idle mixture with pods and i ended up having the mixture screws out 4.5 turns... You could try this and check your plugs.. I had a hanging idle a little and it went away when i changed the mixture screws... just make sure you know how far they are already so you can bring them back if it doesnt help anything for you.

 

Hello,

Did you just get this bike? has it been sitting unused for any length of time?

The most talked about thing that I have noticed would be a very detailed carb cleaning.

You could try to run some seafoam in a tank of gas but not a replacement for a detailed cleaning.

Just a thought.

 

clunk test the slides and see if they pass.

my idle was high and it is a little better since I cleaned those up

 

man, I was really hoping not having to take apart the carbs! well, guess I dont have a choice then. Itll be my first time.. Anyone have any recommended carb cleaning for dummies guides?

 

Your idle is rising because you are lean. Lean mixture burns better in a hot engine than a cold one.

If you're 100% sure you don't have vacuum leaks (including butterfly seals) then you're either plugged up somewhere or the mixtures are just plain set too lean.

If it were mine (and I was sure there were no leaks) I'd do a sync and colortune.

 

Here goes a couple you could check out. Enjoy!

http://www.xjbikes.com/Forums/viewtopic ... art=0.html

http://www.xjbikes.com/Forums/viewtopic ... art=0.html

http://www.xjbikes.com/Forums/viewtopic/t=17609.html

 

MiCarl, even if it does burn better when hot, why would it stop high idle at a stop just by giving a quick jerk to the throttle? :S Would that also be caused because of running lean?

Considering Im a total newbie, How exactly do I check to see if Im running lean? I know i need to check the spark plugs.. but where.. and how.. will I get shocked? (yes these questions may have obvious answers.. but im really just getting started!)

So I've checked for vacuum leaks before and sprayed WD-40 pretty much everywhere around the carbs. I'll check again, Im really hoping it would be just that. What are the specific spots i should check for leaks? A picture of carbs with circled areas would be basic and AWFULLY helpful. I really wanna try all the easier stuff before taking the carbs apart

 

Sounds 99% like stuck slides.

You raise a good point Carl, but I do believe the 'quick jerk' he speaks of rules that out.

Weiss - how come you are spraying WD40 around the carbs?

As long as you don't touch the plugs/wires while it's running - no shocks.
There is no residual 'juice'.

Do you have a propane torch? If so, turn it on and leave the gas on, UNLIT, and move it all around the carbs, boots, manifolds, vac caps etc.
If you idle is affected with the propane in a certain spot, you have an air leak.

If it is in a spot that when warm it expands and lets air in, that might be the problem (air leak will lean it out) And that quick jerk might 'tighten' whereever the leak is. But i still doubt that is it.

Sounds like slides to me. In that case, when you get the carbs off, remove the HATS, take out the spring and carefully take out the slide. Get it set in place and let it DROP. If it slides right through, you are OK. If not, and it gets stuck, or there is any resistance, you need to clean the bore. Make sure you be careful with the needle in the body, it needs to sit in the tube in the center of the carb.

If they stick - get some 800 wet-or-dry paper from autozone or simliar, take a small piece and wet it with WD40. Carefully and evenly smooth out the bore, and the exterior of the slide. Redo the clunk test. Smooth? Get it back on the bike and try it!

 

Well I wasnt literaly spraying WD-40 everywhere. But I mean I was trying to find a vacuum leak with it. Apparently it works.. but yeah.. I doubted it was that in the first place because If i did a quick jerk it'd stop..

Dpawl I'll try out what youve said, sounds the most like what can be causing this problem. Ill give it a try as soon as i can and keep you guys updated!

thanks for all the help to date!

 

I'm 99% sure it's not the sliders.
They are slammed shut at idle.
You could tape them all the way open and not affect the idle. (I haven't tried that yet)(and I fully support the "clunk test")
Have you performed a running sync? Place your plugs on some cardboard or brown paper bag and post the pics here.

 

ok well Im lacking the tools to currently take off the spark plugs. Tomorrow evening Ill have all my tools so I can perform everything. But I was able to take off an air filter just to check out the slides and poke my finger in there to lift em up and see if they passed freely.

The slides slide down REALLY slowly. They call this a clunk test but id NEVER hear a clunk coming from this. I lift it up and just goes slowly down. But then again this was tried with the carbs still on the bike, just by taking off an air filter. Would that affect anything?

And while Im at it, timetoride you say sliders wouldnt do anything even if they were taped open.. then what exactly is their purpous?

 

The carb slides must move freely and to get the "Clunk" Test the carbs should be apart and on the bench. You need to have the carb hats off so there is just the slide going down into the carb bore where it goes. If it slides nice and drops right in it should clunk when it hits bottom.

MN

 

The sliders come into play when the engine is making some real horsepower. The Pilot circuit handles the idle, and just off idle, transitioning to a "low speed circuit" which is the smaller "40" jets.
The main "120" jets have a sliding needle in the circuit, varying their effective size. Then there's air balancing jets- - it's quite complicated.
This is why most advise here is to return the bike to a "stock" state of tune.

They slide down REALLY slow when the hats are still on- - that's good !!
That's a check to see that you got all 4 hat seals right- - a check I coulda used a year ago.
They should "clunk" with the spring out.
(umm- - Wizard?)

 

ok ok Thank you! Ill test it all out tomorrow and say what happens. ill check the spark plugs and take pics and do the clunk test. Ill try to even post a video up on youtube so you can exactly see and hear whats happening!

 

ok so I checked the spark plugs (didnt take pics, i was with a car mechanic who checked them out) and they were all running good on the rich side. I mean it does idle great and run great. And I can force the RPMS down when it hangs by letting the clutch go a bit. But today I couldnt even get the RPMS to hang! It just sticks high a while then slowly goes back down. So vac leak is ruled out. I checked the throttle shaft to push it down and doesnt do nothing. So All I have left to do is the clunk test which i dont feel like doing taking apart the carbs and all.

So now It doesnt just hang at 3-4k anymore. it comes back down. after a while, but still. so TIMEtoRIDE.. what are your thoughts? Ill post a video on youtube just so you can see/hear what Im talking about.

 

and forgot to say I tried messing around with the idle mixture screw. It idles fine a around 1050 like its supposed to. It can go up but wont go down. Dont know if thats related

 

Clunk Test.
Polish the Bores.
Since this article was written I have begun using ScotchBrite Pads

http://xjbikes.com/Forums/viewtopic/t=1 ... +test.html

 

you need to sync the carbs while the engine's running, makes a world of difference

 

Ok well, clunk test and syncing it is then, Dont have much of a choice left.
for the syncing, can I do it as described on this forum?

http://xjbikes.com/Forums/viewtopic/t=6 ... izing.html

and if it was running, how would i do that? are there any guides I could use?


(I was gonna post a video on youtube but its currently down!)

 

No, those are instructions for a bench synch.
Look for mano meter, gauge synch or two bottle carb synch in your search.
Look in the FAQ section there is more then one post on this.

 

OK well, Ill have to build up the courage and find the time to properly sync and do the clunk test.

Last question before I take the plunge, the carbs havent been rejetted since the air filters have been changed to pods.. would that cause a problem?

 

Depending on his mixtures, sync, etc... I would think a stuck slide could cause this problem... Lot's of variables.

Take the hats off, springs out, and release the diaphragm (carefully)
Make sure the needle is in the emulsion tube, and drop. Should slide quick and smooth.

Weiss - also on the WD40. Make sure everything is clean when you put it back on the bike. WD40 gets gummy and gross!