XJ750 High hot idle

I've got this XJ750 i've been working on, Hitachi carbs have been pulled dipped and thoroughly cleaned rebuilt etc. For some reason when this bike gets hot after a ride i'll cruise to a stop and pull in the clutch and she wants to wind up to 4-5K and just hang there. The same thing with a high idle while i shift. I can keep it in gear and drag the clutch with the front brake on to get it to drop but it just jumps back up.

The only thing i can think of is the slide sticking, throttle plates?? I can get to 3 of the slides from inside the air box and they all move freely. When i assembled, i made sure to check all the diaphragms were installed correctly, i was able to blow into all 4 of the ovaled air passages to make the slides raise. Replaced the intake gaskets. Any amounts of brake cleaner around the carbs while running has no ill effect for vacuum leak. Throttle cable isn't binding, plates open and close with good tension. I'm at a loss.......... Anything would be appreciated guys/gals.

Thanks ahead ~Gavin

 

I'm having the same difficulty with my 82xj650 as we speak. I had the carbs cleaned, throttle & choke cables free, and I'm baffled. Then, I read last night in Haynes that part of the problem could be the balance of the carbs. In order to get that totally right, you need a vacuum set up that pretty much only certified shops have to do the job correctly, otherwise it's a guessing game. The other issue that could affect/cause the high revs is a hole-filled exhaust system (affecting the vaccum and causing the extra fuel dumping into the carbs for the high revs)
We'll have to keep working on this one! Let me know and I'll let you know...everyone is pretty good about setting straight all the newbies here (in a nice way!) I've learned SO much SO fast! Eager to do/learn more

 

Sync your carbs by following this thread
http://www.xjbikes.com/Forums/viewtopic/t=2132.html

As for you issue Juice.
If a sync does not do the trick...throttle shaft seals may need to be replaced.

 

Same with my Seca 750 - 1981. I throttled it down to idle at 1050 when warm. However, it idles lower when cold and often need to give it gas at stops. When warm, will sometimes run high at stops. I thought it needed carb cleaning and sync. I'm new to mechanics and have been putting this off because I can ride through it and don't want to delay riding now. Keep up date with any progress you are having. I did run seafoam thru the gas and this was helpful, but still does it.

 

Kayaker,
that IS a clogged starter jet thats causing your problem.
clean them this winter and you will thank me.

 

I thank you now Ass.Fault. I am guessing this is in the carbs. I suppose there is no easy fix other than taking the carbs off and cleaning them. I appreciate your info and not saying do it now because I can ride in the meantime. I love riding it, despite the flaw and I hope it doesn't hurt to ride it like this. I am sure I'll enjoy it more once it is corrected.

 

You don't need a Certified Shop to tune your own bike right to the razors edge of fine tuning.
You just need patience and a couple of special tools.

You can Synchronize the Carbs in a half-hour to 45-minutes using only one Vacuum Gauge. Shops did it that way until the advent of gang vacuum gauges and Mercury Column Carb Sticks.

You'll get them just as Synchronized with one vacuum gauge as you will with a ganged set or Sticks ... It's just going to take you at least 15 -to- 20 minutes (or more) to do it.
The only down side is that you won't get your jollies looking at four columns
or guage faces doing the chore.

The Cardinal Rule of Tuning is: Don't make more than one adjustment at a time.
If you do ... you don't know which of the two adjustments you made brought the desired results.

As for you guys who are having the "Hot High Revving" situation.
Above 17-Hundred rev's ... you are drawing Main Jet Fuel to get the bike to rev high.

There aren't too many reasons why the Bike gets hung-up at High Revs.
Something is keeping the Throttles Open
Look for what might be BINDING

As old as our bike are it not uncommon to have the Throttle Shafts binding in dried Throttle Shaft Seals.
One will affect the whole rack.

Other possibilities:
Sticking Diaphragm Pistons not returning all the way down
Sticking Throttle Cable due to a broken wire un-twisting
Lazy return spring
Air leaking in from Boots and Manifolds

 

Thanks Rick, et al
There's no end to the great information on this site! There is also no end to the MISinformation you'll get "on the street" both from some "mechanics" and/or "knowitall" friends. Since I'm JUST getting into this, I hope that I can sort all that stuff out to take care the best care of my bike. I find the mechanics in my neck of the woods to be about as helpful as a wheel on a crutch so far and no one here wants to work on classic bikes anyway, so fine-I'll learn do it myself (so long as you guys don't boot me off for being a pain!
Thanks again.

 

Boot you off for asking questions?
No way!

That's how you get the Bike fixed around here.
You are better off asking BEFORE you do something so you don't get messed-up by trying something without asking first and getting into a bind.

If you have some spare time ... you can try doing a few search functions in the archives.
Type-in a Keyword about what you are doing and see what to do or what happened to others.

Please find your Signature Feature and add the following info so we dont have to go looking.

Year - Model - Miles - Stock or Mods - General Condition.

 

Sticking / Dirty Diaphragm Pistons not returning all the way down..

That solve my hot high idle probs.

 

RickCM - thanks for the advise. I know from prior posts that I need to clean and sycn the carbs. I'm in denial because it scares me to pull the carbs out. I hear you saying it is not a big job nor will it take long - but it worries me and I don't want to risk not being able to ride it. I know I will enjoy it more when it is running right and the feeling of success when it is done. I am also unimpressed with the "mechanics" in the area and feel they will not do a good job and cost me lots of $ - I'm cheap.

 

a manual + a regular biker = better than a nowadays bike mechanic.

those guys will do what it takes to get you back on the road, nothing more
you can do it THE RIGHT WAY and not have to worry, or worry less

 

Thanks for the vote of confidence Ass.Fault.

 

Kayaker I'm by no means a mechanic but with the instructions and help on this site you can do your carbs. You just need a decent amount of mechanical skill and use the correct tools.

Couple that with patience (take your time) and organization and you won't have any problems.

If I could do it you could too. I had a basic understanding of the carb function from maintaining other bikes but from the folks on this site I now know in depth how my carbs work. Good feeling and handy if something goes wrong.