High RPM issue

[BlkMage]

Carbs were NOT dunked in cleaner when rebuilt, just sprayed. On the '81, the idle mixture screws are NOT adjustable, they're capped off at the factory. But I will try that trick forcing the butterflies closed right now...just might take a second, as the problem seems to only come when the bike warms up.

[dragxs11]

I'm getting curious to see this for myself, and I'm up for an evening ride. If you want me to come down, send me a private message with your add. I can try to make it tomorrow around 8.

[BlkMage]

Update: I couldn't reach all the way in to push on the throttle linkage, but I CAN say that there was resistance and the linkage was going all the way down. In fact, I could rev it up more by giving it some throttle. Oh, and the cylinders with the needles were not moving when it hit the higher RPMs like they were when I first started the bike and gave it a few twists before the problem came back.

Yea, I'm starting to realize how sure it is that there is an air leak, but I still can't find it!

[Ken Talbot]

Originally posted by BlkMage
On the '81, the idle mixture screws are NOT adjustable, they're capped off at the factory.

Capped off does not mean they are not adjustable. It only means you have to remove the caps to get at the adjustments. If the caps have not been removed, there is no way you could have done a proper job of cleaning the low-speed circuits ont he carbs, no matter how much carb cleaner you spray or how much air you blow. Those caps have top come off, the low speed circuits have to be cleaned, then you can get back to doing a sync and setting the pilot screws.

Sorry...

[BlkMage]

Originally posted by Ken Talbot


Capped off does not mean they are not adjustable. It only means you have to remove the caps to get at the adjustments. If the caps have not been removed, there is no way you could have done a proper job of cleaning the low-speed circuits ont he carbs, no matter how much carb cleaner you spray or how much air you blow. Those caps have top come off, the low speed circuits have to be cleaned, then you can get back to doing a sync and setting the pilot screws.

Sorry...

When I said "capped off" I meant kinda permanently. Unless I want to break out a hammer and chissel and chance spliting the carbs wide open.

[ratbyk]

I'm not sure on your bike but all of the XS's I've seen with the plastic caps. Well you can put a screw driver under the edge of them and lever the cap off. They can then be adjusted. Your option as to whether you want to put the caps back on.
If and when you go to adjust the idle mixture screws, DO NOT FORCE THEM DOWN TIGHT! The tapered needle that you are screwing down will enlarge the bore it is screwing into and make idle mixture adjustments difficult in the future. Another problem with this is that on a fairly regular basis people jam the needle into this bore then break the tip of the idle mixture screw off blocking off all fuel for idle.
As you turn the screw down, as soon as you meet resistance, STOP. I would run the screws down to the bottom, stop, then back it out 2 complete turns. Start the engine up/warm up then slowly adjust the screw down/up until you reach the highest RPM then go onto the next carb. If the idle gets above 1000RPM adjust the idle speed down before going to the next mixture screw.

[ratbyk]

When I said "capped off" I meant kinda permanently. Unless I want to break out a hammer and chissel and chance spliting the carbs wide open.

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If you have the sealed plugs covering the idle adjustment screws (like a frost or Welsh plug) Drill a small hole into them, (be shallow with the drill bit, just puncture the surface) Then screw a self tapping screw (sheet metal screw) into that hole, lever the plug out with pliers/vise grips.
Then go ahead with the adjustment as in my previous post.
Oh ya, as Ken Talbot said, if these screws were not removed during the carb clean/they have not been cleaned completely/properly.

[TopCatGr58]

Okay Mage,

First....you stated the carbs were synch with the butterflies, but this is just a PRESYNCH, a vacuum synch needs to be done, but not until you find the vacuum leak.

Secondly, those brass caps are removed by taking a small drill bit and drilling about 3/16" to 1/4" down, they are not very thick, and then put a sheet metal screw into it, and then grab the screw with pliers, vice grips, whatever, and wiggle it to knock them loose and remove. Just put some tape around the tip of the drill bit to mark your depth, and go lightly so you won't pop thru too quickly to damage the pilot screws beneath them!
T.C.

[Ken Talbot]

The good news is that with the later-model carbs on the '81, you don't have to worry so much about jamming a pilot screw in its bore. The later-model screws are the blunt end type which are not so prone to getting stuck and breaking off. This is good.

[BlkMage]

Thank you dragxs11!

He came down yesterday night for a look, among other things playing with my idle adjust screw, and it worked! I took her out for a run just a few minutes ago, stopped after a while for a final tweak, and it's all set! Thanks again everyone, see you at Tahoe!

[ratbyk]

Happy for you. Now ride the sucker and stop fretting.

[grakyody]

High RPM issue

Hey BlkMage,
What did you figure out on your problem. I have the same problem with my 80 xs special.

[grakyody]

High RPM issue

Never mind, I found it. Duh.. It's the little things that eat your lunch!