idle issues

[81' xj650 Maxim]

So, after getting the boots patched up things seemed to be running well. However, it seems to be changing over the weeks now. I'm not sure if it is the extra heat or what exactly.

Symptoms: Unless it is in the 90s out, when i start the bike, it threatens to die unless I have a fair amount of choke in. After a half minute or so, I can relax the choke most of the way out and start going. Once I get out on the highway, I get the choke moved all the way off.

My commute to work is about 20 minutes. On hot days, or longer rides, by the time I get back into the land of traffic lights, when I stop and hold the clutch or put it in neutral, it idles in the 3-4k range. I manage this by slipping the clutch back out some and letting the engine pull, but it isn't ideal.

The high idle problem only happens once the engine is very warm, and seems to be worse on hot days. I wouldn't think a few degrees of ambient tempurature would make that big of a difference, but it sure seems like it. It didn't do this when I first got it running again, but the average outside are temps were 10-20 degrees lower at the time.

Does this sound like a carb tuning issue? Could I just have the choke cable messed up somehow from when I put things back together?

 

more likely then not you have an air leak somewherer before the engine. Also in addition to that you might be running rich/lean.

As a temporary solution blip the throttle so the engine (with the clutch in) tops at about 5-6K then use the clutch + 1st gear to bring the idle down to 1-1.5K it should stay down for a while if you dont touch the throttle. This trick has always worked for me when it idles high coming off the highway.

 

OK ... Pay attention 'cause this can really happen. Check how much free-play you have on the throttle grip. If it's really tight (none) that needs to be backed-off a skootch.

Because ... when it gets really blazing hot, like it did around here, last week ... a tight throttle cable at the grip causes a bit of a nagging issue.

High ambient (outdoor) temp + high engine heat causes the throttle cable to expand a bit -- [Heatwave effect] All the 90+ degree heat (it was 108 here) combined with the engine heat makes the sheath expand a tiny bit.
When the sheath expands due to being subject to far higher than normal temps ... it takes the throttle CABLE for the ride. The throttle cable does not expand ... it just moves along with the cable sheath. If there's no room at the grip ... it pulls on the other end--where there's a spring attached. You know the rest! Most cables have a little adjustment knurl to deal with this. Unlock the knurl and give is some room. (works BOTH ways // you can add a few RPM's-too ... when its cool.)

Riding the clutch is NOT recommended. Make the adjustment at the cable or carb rack idle adjustment rod.

 

Riding your clutch is bad JuJU... your going to mess up your clutch discs.
Sounds like carb tuning is in order, if your not up to doing this yourself, I'd suggest a reputable shop or mechanic, someone familiar with these bikes.
XJ's are easy carbs to work on if you know what your doing.
It sounds like you could have a vacuum leak or just sync/mixture trouble.
What do your spark plugs look like? That can tell you alot.

Good Luck
Mike

 

Let us know if you have 1. colortune and carb sync tools. 2. cleaned the carbs before or recently. 3. checked/replaced the air filter. 4. installed an inline fuel filter.

 

Sounds lean to me , out the mixture screw 1/2 turn and see if its better....

 

I recently had the carbs off to try to fix some boot issues, but did not try to tune them. I don't have the tools, and I'm a bit intimidated.

I did pull the airfilter out recently and checked it, but I didn't replace it.

I haven't installed an inline fuel filter. Its possible there is one there though. Where would I look?

 

i *think* i actually fixed the vacuum problem at the beginning of summer, but its possible that the intertubes didn't seal properly or something still isn't right.
(http://xjbikes.com/Forums/viewtopic/t=1212.html)

I'll pull the plugs again and take a look.

 

Some have had success patching the intake boots with RTV. Permatex makes a black colored one that doesn't look tacky. If they are leaking then I would bet that is your problem. HVNBND is right about riding the clutch. It is not good for it. It's one of those things that bites you later down the road. Brian's idea on using it excluded. That could be done just to find out what may be happening but doing it as a habit is bad juju.
Oh yea the inline filter would be on the main fuel line coming out of the petcock.

 

agreed! (see above) i have been using this trick for a little to long, and i think, it be high time i get to the bottom of this! like you said its bad voo-doo... or juju.. well its jsut bad. but it beats slipping the clutch the WHOLE time your at a light to keep from sounding like your ready for T-minus 3... 2... 1... LIFT OFF, and generally looking like an ass.

 

Brian has a point here. Here we are riding one of the coolest bikes on the road....... looking like an ass is not an option!!!

 

My bike was doing the high idle thing for quite some time, and I couldn't engine brake for crap. I ended up turning the idle screw out a bunch, and it fixed my problem! Of course, the engine wouldn't idle by itself then either, but....

I did a valve clearance adjust today, and the bike (almost) idles all by itself now! I can hear cylinder 4 firing now at idle, while it obviously wasn't before. MUCH better riding too, and alot smoother.

 

Where's Rantoul, IL? I'm in McHenry(NW burbs of Chicago), and I have a carb sync tool. Have yet to do it to my bike, was waiting on the valve clearance issue first. Could end up having a carb clinic here in IL!

 

Yep. My Xj is the only thing that makes me look cool! Speedwagon, if you want to do a carb clinic let me know. I can't make it there but I will ship you guys my colortune to use so long as you ship it back.
BTW..does Gary Richrath know you are using his Rock band's name?

 

Rantoul is about 20 minutes north of Champaign-Urbana. I grew up in Elgin, so I know right where McHenry is.

A local carb clinic would be great. I'm not a complete klutz, but for some reason I'm intimidated by tearing down the carbs.

 

Speedwagon, That worked for me too (Idle screw thing)

 

The idle screw is the thumb screw on the underside of the carb right? Clockwise to increase idle and counter clockwise to decrease?

 

Gabar, the secret is in pictures with that digital camera.....lots of pictures!!

 

Its a large starlike thumbscrew in between the 2 middle carbs,behind carbs in front of air cleaner. screw in to decrease out to increase.

 

If your offer to ship your ColorTune to members having a clinic ... we'd be very happy to have you loan the instrument to us for our upcoming clinic on the weekend of August 19 & 20. I'll accept the responsibility for its correct use and handling and ship it back on the Monday following the event.

Rick Massey

 

Rick I sent you a PM on this.