Need suggestions XS1100SF

I've got an XS1100 in the shop that has me pulling my hair out.

It's got a severe case of hanging idle. 2500RPM then drops to 1000 or so, stumbles a few times and dies.

No evidence of vacuum leaks. Disconnected vacuum advance and fuel valve with no change.

I've been through the carbs a half dozen times. Everything there seems to be ok. It won't idle at a reasonable level long enough to use a color tune plug.

A neighbor machinist made me an adapter to put a fuel level hose on the bowls. Levels seem reasonable, although the Clymer manual specifies a float height rather than a fuel leve.

Anybody got any suggestions what I'm overlooking?

Thanks.

 

CV carbs? Throttle shaft seals? Enrichment plunger seal gone? When it dies are the plugs wet or dry?

How about things like valve clearances and a compression test?

You mentioned "vacuum advance" does this thing have electronic ignition or points?

 

A buddy of mine used to run an XS1100, I still have an XS850SG in my home garage.
That being said...

Charging system, battery voltage? How's the reg/rec check out, plug wire resistance/plugs?
Those bikes were never particulary picky about fuel levels, but low battery bothers them quite a bit.

Few questions...
Standard air box or running pods?
Are the exhaust pipes providing good back pressure?
Oil level in range, not too high (almost sounds like it's choking itself out)
Is the Choke throw fully returning?

besides making sure fuel is being delivered, what else have you done?

 

I am sure you have probably done all this but just in case you overlooked anything always good to hear what everyone says. I thought advances were mechanical on older bikes with points but i could be wrong. Did you try spraying the carbs and boots with anything to see if idle would come up that will usually tell you if throttle shaft seals or boot is leaking. Also if you have carb stix see if they are closely synced that will usually tell if you have a major leak or if 1 cyl is bouncing more then others tight or burnt valve or low compression. Like fitz says a to tight valve will mess things up bad. In my experience hanging idle then dropping off and dying usually 1 or more carbs are out of sync and your trying to adjust the others to make up for the ones that are out. If your slides are sticking might have a little effect did you do the clunk test? 1 thing i forgot to ask it does have the airbox doesn't it.
I have a heck of a time especially late 70s early 80s Suzukis without the airbox they do the same thing. I have to take a rag fold it over and put it over the carb inlets man they are jetted so lean at idle. Wish you the best of luck i hate problem bikes but usually that is the ones i usually have to work on.

 

You could try the pick up coil wires.
They are notorious for breaking due to the movement that is caused by the vacuum advance.
Take the side side cover off and then try wiggling each wire in turn. A sure sign of the problem is also the shape of the wire at the breakage as it tends to be in the shape of an hourglass, you know fat at the top and bottom and thinner in the middle.

Also have you tried adjusting the idle mixture screws. Should be 1 and a quarter turns out from the base.
That could also cause a problem.

I've got 2 of the XS1100's and any help i can give just ask.
Also try www.xs11.com or www.benefiscal.co.uk/forum

 

Valve lash was done - forgot to mention that.

They are synced at high idle. They're certainly close enough that it should idle.

Stock air box. Pipes are not stock, but not open either.

I've drenched it in enough starting fluid it's quite amazing I haven't blown myself up. No effect.

Yes, it has mechanical and vacuum advance. But also TCI.

I've tried disconnecting and grounding each plug wire to see if I could identify a cylinder cutting out. It doesn't hang, but doesn't stumble at 1100 either. It just drops and dies - seems to be the same for all 4 cylinders.

I don't think it's low voltage. Been working on it with a charger connected. I've been burned enough times by low voltage issues on XJs to watch for that.

Plugs are quite dark, but dry.

I'll check the pick up coil wires tomorrow, but doubt that is it. This is predictable enough I can set my watch by it. I'd expect a problem wire to be more erratic.

I've been working with the mixture screws 2-3 turns out. About the only effect I've seen is I can make it miss the stumble and just die if I turn them in. I'll try tomorrow closer to 1 1/4.

There is one mixture screw where the point was broken off in the body. It was tight enough that digging it out made the hole bad enough it snapped a new screw. What it's got is a modified screw with a very steep point. I believe it will close completely, and of course even one turn should make it quite rich. That screw doesn't seem to have any different effect than the others. I know this is possibly the culprit, but need to weed everything else out.......

 

Forgot to mention - good compression too.

 

There are two different types of pilot jets that will fit the XS11 carbs but only one will work.
Look at this link to see the difference.
http://www.mikesxs.net/parts/Mikuni_Jets.gif
I'm almost sure your XS needs the 4 hole VM style jet. If the other one is installed it will make the idle mixture impossible to set right and the idle speed acts just like you describe.
If you pull the carbs again I would also check that the enrichment plungers seal. The rubber washers on the ends do tend to crack and come loose. Any leaking there is not good. I test mine by putting a 1/8 silicone tube over the bowl pick-up and pull a vacuum with a hand pump and see if it leaks down.
Throttle shaft seals are my next thing. I have had similar problems that were solved with new seals even though I could not find a leak with starting fluid.

 

The XS uses BS34 carburetors. One did have a VM style jet but I caught that several iterations back. You are right though, the one with the VM jet wouldn't lean out.

 

I have a 1977 XS650, I remember when the springs of the automatic advance mechanism were weak, the idle would often hang up at 2500-3000rpms. Are you sure yours are good?

 

Burnish and Polish the Diaphragm Piston Bowls.

Treat the Throttle Shaft Seals.
Long-ago, we would use TEAC Pinch-roller Rejuvinator.
That went the way of the Walkman.

This stuff might do the same trick.
http://www.parts-express.com/pe/showdet ... mpaign=pla

Look at the Rack Fasteners.
It the Rack Fasteners look "worked-on"; check for alignment.

 

TEAC Pinch-roller Rejuvenator??

WHOA....holy reel to reel!

 

No I'm not. I think the advance mechanism is buried behind the pick up plate on this beast. Surprisingly it's still available, but not inexpensive. I may have to find a way to disable it as a test.

Everything on the rack looks like a joint effort between Fred Flintstone and Homer Simpson: Broken float pin tower, pilot screw broken off, wrong jets, missing washers etc. etc. etc. I'll check alignment next time they're off.

I'm seriously considering punting on this one. Will be my first and hate to do it but it's costing me a lot of valuable time.

 

Can't blame you there. Punting is half as good as a touchdown. You can always tell him that you'll trade him the work for the title...

My dad had a poor mechanics wreck of a '83 Vision that I have properly mechanically and electrically resurrected. He gave me the bike in the end after a full carb rebuild, electrical system overhaul, enging gaskets, brakes, etc. I probably spent more on ti getting it running then he did buying the thing in the first place.

 

The only possible reason for doing that would be for the right to shoot it!

FJ111200's suggestion of 1 1/4 turns on the pilot screws helped.

I checked the timing and both the centrifugal and vacuum advance. Everything there seems ok per the Clymer manual.

What is happening is when the throttle is blipped the vacuum advance moves the timing forward about 20 degrees, which the motorcycle likes. Eventually the advance creeps back, retarding the timing and it stalls.

By forcing it to advance I was able to get it to run stable and get synced and tweak the mixtures. Then I was able to fine tune it at 0 advance.

It still hangs a bit, but way better than it was. The thing idles a whole lot better with some extra advance but don't want to force that.

The idle vacuum (without extra timing advance) is poor. I'm going to attribute that to the buggered pilot hole on the one carb and send it home.

Thanks guys for your feedback. It helped a lot hearing your suggestions.

 

You have got the tube from the vacuum advance going to the spigot on number 2 carb and not to the spigot on the number 2 inlet manifold haven't you?
JAT.

 

Yes.

 

CV carbs are unbelievably sensitive to air leakes and un-sync.
Michael

 

CV carbs are unbelievably sensitive to air leakes and un-sync.
Michael