high idle???

[jmnjrpa]

This is an original Yamaha 81' XS1100LH MIdnight Special. I spent 8 months cleaning, painting and plating it. I rebuilt the carbs and rejetted to 120 on outside and 125 on inside cylinders. All original mains were 110 but have MAC exausts and have ditched the stock airfilter for pod style. Also went with a size down on the middle air jets. When I cranked it after a short warmup the idle ran to 5000 rpm. Readjusted carb floats and looked everything over but it has been many a year since I worked on one. The needles and jets were all the same and in good shape. Put in a carb kit (all parts were same as original) with the fore mentioned changes to the mains and air jets but that is all. I even reduced the idle jets to 1/2 turn but it kicked up to 5000 pretty quick. Checked the throttle for issues but butterflies are closed. It revs nicely but when you are already that far up I don't know if it means much. I am at my wits end. Anyone have sugestions?? THANKS!!

[ccogswel]

One thing you did not say that you need to do is. You need to sync the carbs. That might be one cause. The other is you might have a leak in the intake boot. It can may have crack that goes through or the gasket between the boot to head is leaking. Check these things out first. This might fix it.
Good Luck!

[jmnjrpa]

I did a pre sync on the carbs ( adjusted all butterflies to close on .010 shim) although I could not find the specs that should have been a good start??? I refurbed the carb boots with several coats of Plasti Dip to insure they were crack free (the spray on allows for multi coats and spot work). Sorry, you probably know about that. Anyway, good points, but I can't see how the RPM's are so high. Am I wrong?? Could there be enough air flow in leaks and/or not having the butterflies close completely? On a whim, I ran the bike without air filters and did not see any change. Looked past the needle jet and could see the butterflies were closed. It does appear to be running rich but haven't comfirmed that. No leaks and floats are doing their job even tho I originally had 2 that weren't. I set the float height to specs but I read in the forum that may not work. If I shut the air flow from the filter side ( to comfirm no air leaks) it should kill the engine. Is this a bad idea? I used to work on my bikes when I was much younger but cant recall ever doing anything other than tuneups and carb kits. Thanks

[John]

Have you tested the throttle shaft seals for leaks? An unlit propane torch is good for this. Just open the torch valve and work the torch tip around the arear of the carbs where the shafts protude. Check the joint of the boots to the head also. Another item to check is the caps on the vacuum ports on the intake boots. They can get hard over time, and not form a good seal anymore.
Also, have you checked the throttle cable adjustment at the twist grip?

[bikerphil]

Did you use the main idle adjustment to try to lower the idle?
Is your vacuum advance hooked to the #2 carb body and NOT to the carb boot?

Simple questions that needed to be asked.

[jmnjrpa]

Thanks John and Chris. Too dark now but I got all day tomorrow.

[ccogswel]

John your a fast one. Beat me to it as that's what I was going to say.

But as for sticking you hand on the back of the carb to check for leaks is a bad idea. The only thing your going to do there is cause it to suck more gas into the cylinder and that will make it run at higher rpm too. Besides that your not going to kill it with just doing it to one carb as you have the other 3 still working unless you try all 4 at a time. But still a bad idea. If you want to try it tho you can. I just don't see it helping you out any.

If I remember you said you checked but just to make sure check your throttle cable. Make sure you have some play in it. This will cause a high idle as well.

Good Luck!

[jmnjrpa]

Thanks Bikerphil. I did set the idle at the carbs or tried to (did not change it). Yeah the advance is correct and the boots are all capped off. I have a powerfull urge to pull my hair out!!

[jmnjrpa]

Thanks Ccogswel. Just had an idea that I could place a piece of rubber across all intakes and it should kill the engine (do to no oxygen for combustion). If it did not then it should point to leaks??? I wondered if maybe this was not a good idea do to something I wasn't considering. I still can't believe this thing doing over 5000 RPM unless it is opening the butterflies. Of course I can't see that when it is running, or can I (light bulb went off or DUH out)? Thanks again!!

[Ken Talbot]

Pre-syncing the carbs via the bread-tie method will get all four carbs reasonably close, but will always result in a high idle. Bring it back down with the idle speed adjusting screw and you'll be in business.

[jmnjrpa]

Thanks Ken. I actually used a method we use in the machining industry. Simply used a 1/2" strip of paper (this will average .002"/.008" thickness- with copy paper being on the low range) and adjusted each carb in proper order until the paper did not slip out of the butterfly. After adjustment gave the throttle linkage a couple of good thumps and rechecked. I then set the gap with the Idle adjustment screw to a 3 sheet gap (.010"). This is a highly accurate method that will not damage the bores. I used 3 pieces thick to set the idle but I believe today I will reset to .002 and follow all the other good suggestions I got here. I will be back with the results later, after a ride or cry in my beer.
Thanks everyone. I will post pics then or after the ride.

[TopCatGr58]

This is an original Yamaha 81' XS1100LH MIdnight Special. I spent 8 months cleaning, painting and plating it. I rebuilt the carbs and rejetted to 120 on outside and 125 on inside cylinders. I even reduced the idle jets to 1/2 turn but it kicked up to 5000 pretty quick. I am at my wits end. Anyone have sugestions?? THANKS!!

Hey JMN,

The bolded text above sticks out to me. The stock setting is 1.5 turns out. The pilot screws are fuel/air mixture screws, and turning them that far IN is setting it very lean, which could also contribute to a high idle. I'd suggest resetting to 1.5 turns out.

The 81's also utilize a small metal and rubber o-ring down inside the pilot screw tunnels, they get stuck, don't always come out, etc. No aspersions on your skills, you sound very knowledgeable around machinery, but these carbs can drive the best a little crazy! Just checking, hoping that you didn't actually SOAK the carb bodies in any carb cleaner, vs. just using carb spray cleaner?? Hence the previous suggestions regarding the butterfly shaft seals, which are damaged with soaking in harsh caustic chemdip type cleaners.

The rubber that is molded around the intake boots dries, hardens, cracks, crumbles, etc. and can cause a vacuum leak where it mounts to the head, so a gasket and even some sealer is suggested to ensure a good seal. Also, the synch port caps can feel like they fit, but also harden, and leak, simple replacements available at local auto parts store.

Your precise bench synch is a good start, but a vacuum synch is still highly suggested for a proper final tuning and balancing of the carb bank. Also, did you inspect the rubber diaphragms of the vac. slides for pinholes, test them by lifting them up, blocking off the top arced vent, and see how slowly they drop.

Just a few thoughts!
T.C.

[jmnjrpa]

Thanks TC. I adjusted the idle screws in an attempt to idle it down. Will check all the other good advice as soon as I check on the intake valve on cylinder #1. It developed a back fire thru the carb that I could see when air filters were removed. Have the valve cover off and the cams look real good. Hope I only have to adjust the intake.(fingers crossed).

I bought this bike thru Ebay last summer for 1200 USD.The previous owner had purchased a HD and said the MSN had just been tuned that spring. Yeah, he got it running but that was all. I had always wanted one and this one looked pretty good. Intended to return to better than original - all real gold plate (no chrome or bare aluminum), black cerimic pipes and black chrome. By the way I purchased a plating system for gold, silver, nickel, copper and black chrome. Actually cost about the same as having all the plating done. Also am buying a painting system for exotic coatings. This will enable me to offset some of the expences.

Expected to have to do some work on it but when it arrived the petcocks were leaking sooooo-- I stripped it down to bones and started. Worked on it all of 7 weekends before winter set in.

You guys are great!!! I appreciate all the help. I will add pic as soon as I figure out how. I have one from last week that is almost complete -missing the air pods and additional plating/painting on the chrome pieces.

Thanks all!!

[jmnjrpa]

Let's see if this works---http://www.facebook.com/album.php?aid=22621&id=1212170600&saved#/photo.php?pid=496816&id=1212170600

[Crazcnuk]

"adjusted the idle screws in an attempt to idle it down"

You don't use the idle mixture screws (4) to adjust the overall idle speed.

There is a large adjuster thumb screw in the center, under the carbs, angled towards the motor. This is the idle screw they are referring to.

The 4 mixture screws should be adjusted to get the max smooth idle, then use the idle screw to bring the idle back to normal.