What does an idle sound like?

[Incubus]

Only a half facetious question. I've heard my Honda 750 idle, my Duramax idles nicely. my Honda 400 idles. Even all my dirt bikes idle.

But my XS11? Carrumbah!

I've fixed the shudder that afflicted the bike. Now it powers nicely through all rpm ranges and is very sprightly when in motion. No slippage. But it never comes back down. First gear is a memory. Ever try to downshift into first at 3,000 rpm? It ain't pretty.

My carbs are so clean that the local hospital wants to perform surgery in them. I used a whole carb of B-12 on the choke circuits alone. New carb holders. New air jet needles, set 1.5 turns out. New air filter.

I thought I fixed this several times. It works for a while, then no more. So I haven't found the root problem yet. Here's symptoms. When the bike is on full choke at start up, it runs well, then after a few seconds the idle starts to climb. Goes to about 3,000 rpm if I leave it alone. If I take it off full choke to half choke it's fine for a while, then it starts climbing again. It will go to about 2,000 rpm. When it's warm and I take it off choke it refuses to idles at 1,000. It will idle great at 2,000, but then it's hard to get it into first. If I turn out the throttle screw to get it back to 1,000, it will die. It will not idle at 1,000.

I bench synched the carbs and then synched them on the bike by holding the bike at 1,000 rpm with the throttle. This is what makes to sense. Why can I hold it at 1,000 rpm with the throttle, but not the throttle screw? It synchs real pretty - all four needles in all four gauges rising and falling together like the Rockettes' legs.

But then it won't idle. I've been over this so many times that I don't even remember what I've done so far. Can anyone help this poor hapless wrencher?

Patrick, owner of faithless lover Succubus

[oseaghdha]

Vacuum leak?

[Incubus]

That's something I've considered, but I'm not sure where to look for one. I have new vacuum lines, properly connected. Carb clamps tight. New carb holders. Where else could the vacuum be compromised?

I am open to any suggestions. I frankly am at my wit's end. I've never had this kind of trial with an engine. Maybe I need another hobby. Needlepoint, perhaps. Basket weaving looks pretty entertaining...

Patrick

[cruiser]

2nd vote for vacumn leak.
Get out the carb spray and spray around all joints while running.
I located mine (XJ)at a small split in vacumn line to carbs. Not very visible to naked eye but spray found it every time.

[81xsproject]

could you better explain how you are "holding" the rpm at a 1000, but it won't Idle down to 1000 at the screw? Are you opening the throttle above 1000 with your hand and then, while continuing to hold it, backing out the idle screw, and then with your hand, backing off the throttle down to 1000 and holding it there?

[Incubus]

If I loosen the throttle screw below 2,000 the idle drops and the bike dies. If I start it with the throttle screw already loose by twisting the throttle a little, then I can hold the idle at 1,000 with the throttle. There just doesn't seem to be anything the screw can do between 2,000 and dead.

[Tdog]

no idle

Stickey vac. advance? Vac leak gave me similar prob. on my '72 CB500.
Tdog

[81xsproject]

Have you tried disconnecting your throttle cable from the carbs and running it? Sounds almost like a linkage issue, but weird. What about float levels? What do your plugs look like?

[TopCatGr58]

Hey Patrick,

It sounds like Potato, potato.....or wait a minute, that's for only when it's running on 2 cylinders!

Okay, you can twist the throttle at the handlebar and keep it idling at 1000 which means you're opening up the butterflies to get more fuel more than just the pilot circuit. But when you use the throttle/idle set screw it will only idle if set to 2000, once you start backing it out=closing the butterflies, it dies. Again, running out of fuel. Some how I think you are not holding it exactly still with the handlebar throttle lever so may not be an accurate 1000 idle.

Anyways, try turning out your pilot screws which are FUEL/air mix screws, not just AIR screws, will richen it up a touch, and may give you enough fuel flow to keep idling at the lower rpms.

Turn them all out 1/2 turn at a time, and then try resetting the throttle/carb idle screw and see if it will hold at 1000 AFTER warmed up. IF not, try another 1/2 turn out.
T.C.

[dale_1]

vac leak advance unit???

does this model have the same vac advance as on the 81? I had to lube the mechanism because it would start to stick.... (took off the left cover and sprayed civilian version of VVL-800 gun lube at the plate behind that swiveled when throttling up). Mine would advance and then not come back (or is that retard?) after lubing the mechanism that the vac advance moved at all points it has settled down a bit. But it is tough getting that perfect spot. Now mine idles at 1100 until I have been on it really hard and then it idles about 1250. I can live with that. Mine was doing the same thing.

Also.... if yours does have the vac advance on the left lower that is a vac hose going into the top of left side. inside or outside of the cover may have a leak. Found one of those once long time back. Sprayed everywhere but no changes..... until I pulled that side cover.

[prometheus578]

I will work on the assumption that the carbs are clean, and all passages in perfect order.
The throttle cable and the idle screw operate against the same mechanism. Both do the same thing. The cable pulls the mechanism which opens the throttle plates a little. The idle screw pushes against the same mechanism which open the throttle plates a little. Both do the same job... one is quickly variable(cable) and the other, while variable, takes time to turn in and out, adjusting the engine speed. As the cable works fine, the only other issue here is the idle speed screw.
You may need to pull the carbs and make sure that the end isn't bent or mis-aligned. When turning the screw to lower the idle, does the idle go down slowly to die, or does it go down slowly, and then suddenly die? Is it possable that the tip of the screw is bent, or the whole bracket that hold the screw is mis-aligned?? What would happen here is that, as you're slowly turning down the idle, the tip of the screw slips off it's adjusting plate, and the throttle then slams fully shut. Could the threads on the screw be stripped?
Geez, I wish I could be there to see this one in action!

[Incubus]

A bit more detail...

When it is idling at 2,000 I turn the throttle screw out slowly. The engine speed begins to come down slowly. But then it keeps coming down slowly until it dies. It doesn't seem to matter if I stop turning the screw and I only have to turn it a little. Once it starts coming down it doesn't stop.

I've tried turning the screw all the way out, starting the bike and then, while holding the idle with the throttle, turning the screw in slowly just until I can release the throttle without the engine dying. But as soon as I can release the throttle, the idle climbs again to 2,000 rpm.

I am doing this using only the bike's own tach to gauge the rpm, so I can't swear that it is exactly 2,000 rpm, but it clearly is a high idle and it clearly grinds when I try to put it in first. It goes into first nicely if I am holding the idle with the throttle.

She is laughing at me. Succubus is laughing at me. I'm thinking she was enjoying her 15-year hiberation and really isn't happy that I disturbed it....

I'm going to pull the vacuum advance again tonight and check it again. At one point in this process it was sticky. I lubed it and it was moving smoothly, but it might be sticking again. I also have plenty of vacuum line, so I'll replace it all again just in case I punctured something during one of the many times I've pulled the carbs.

I am going to figure this out.

Patrick

[webbcraft2150]

We could pull the carbs off my 80g and try those on your rig. Don't really know if being a newer model, it would cause any big problems (you guys chime in here). If it works on my carbs, then you know you have a different problem. Are you running a stock airbox? I know your getting frustrated, but don't let that nappy tired rig get the best of ya. You using a carb stik or gauge style? I would lean (no pun) toward a vac leak also, but it sounds like you have covered all those bases. Did ya "read" the plugs? A toasty plug would indicate a lean mix.

[DiverRay]

Just a thought, did you REPLACE the caps on the non used carb holders? I would also put the petcock on "prime", and plug the lines at the holders. You may have a leak in the fuel petcock assembly. The spray can of WD40 or B12 can be used WITH THE STRAW to find any leak. Don't forget to check around the butterfly shaft, as one or more of the seals may be out.