Stumbling

[HalfCentury]

Drove the XJ1100 several times and it runs like crap.

Pulled the plugs. #2 was wet and very black/sooty. None of the rest are wet nor sooty.

I have never traced down coils/caps/wires. Where do I start? I have good multimeters.

[BA80]

2 & 3 are on the same coil and fire at the same time in this wasted spark system. Swap the 2 & 3 plug wires and see if the problem moves to the #3 cylinder. If it does it'll either be a coil or a plug wire/resistor cap. If not it will be a mechanical/carb issue.

[HalfCentury]

2 & 3 are on the same coil and fire at the same time in this wasted spark system. Swap the 2 & 3 plug wires and see if the problem moves to the #3 cylinder. If it does it'll either be a coil or a plug wire/resistor cap. If not it will be a mechanical/carb issue.

The problem remains at plug #2 so its not an electrical problem.

I may be able to check the float height without dismounting the carbs. I assume that is one of the first things to look at?

Also the number of turns out the pilot screw is?

[Bonz]

Check all the pilot screws, for a reference to see in general where the are set, see if #2 is way different than the others.

Tap with a screwdriver handle or something similar on the float bowl to see if the float maybe sticking, that may unstick it. In my experience floats just don't go WAY out of adjustment on their own. You can also remove the bowl drain screw and shoot some carb cleaner up in there as well. May dislodge a stubborn piece of debris that is causing the float needle not to seat fully.

Have you pulled #2 plug and attached the plug cap and visually checked if you have any spark? Probably you have established there isn't a spark, but it's an easy check.

[BA80]

The problem remains at plug #2 so its not an electrical problem.

I may be able to check the float height without dismounting the carbs. I assume that is one of the first things to look at?

Also the number of turns out the pilot screw is?

Could be the plug also. You might swap that out before you start.

[HalfCentury]

Check all the pilot screws, for a reference to see in general where the are set, see if #2 is way different than the others.

Tap with a screwdriver handle or something similar on the float bowl to see if the float maybe sticking, that may unstick it. In my experience floats just don't go WAY out of adjustment on their own. You can also remove the bowl drain screw and shoot some carb cleaner up in there as well. May dislodge a stubborn piece of debris that is causing the float needle not to seat fully.

Have you pulled #2 plug and attached the plug cap and visually checked if you have any spark? Probably you have established there isn't a spark, but it's an easy check.

I did not perform a spark test with the plug resting on the engine. I did swap the wires so that wire#2 was mounted on to cylinder #3. Wire #3 was on cylinder #2. I pulled both plug #2 and plug #3. After a ride around the neighborhood, plug #2 is fouled and plug #3 remains dry and looking good.

This tells me that the coil and wires and caps for #2 and #3 are good.

This means #2 is either starved for air or over enriched with gasoline, yes?

I like the idea of shooting carb cleaner up into the bowl drain opening. I will try this after I hook up hoses to check float levels.

I also like the idea of swapping the plugs. It cold be a bad plug. If only it were a bad plug. That would be awesome.

[Bonz]

Yeah keep us posted!

[HalfCentury]

I hooked up a clear tygon fuel line to carb #2 drain nipple. There was a large air bubble just after the drain nipple that would not go away. I used a large syringe to push the air bubble back into the carb bowl and then removed the syringe. Now there is no air bubble.

What I am wondering is if by pushing the air bubble and fuel back into the bowl, I overfilled the bowl?

As of now, the meniscus on the tygon fuel line is 5.5mm above the bowl gasket.

What is the magic distance from the bowl gasket for a properly set float?

I am going to push the bike out to the driveway and run it with the drain screw open and the tygon line in place. I want to make sure I have measured the fuel height in the run condition.

[BA80]

Should be about 3mm BELOW the top of edge of the bowl.

[HalfCentury]

Nobody guessed that the idiot who installed the plugs did not properly gap one of them. Noticed the disparity in gap when I swapped #2 and #3 to see if the problem followed the plug.

After adjusting the gap down, no more sooty plug.

And....the fuel height in #2 is a couple of mm below the gasket while the engine is running.

[HalfCentury]

Nobody guessed that the idiot who installed the plugs did not properly gap one of them. Noticed the disparity in gap when I swapped #2 and #3 to see if the problem followed the plug.

After adjusting the gap down, no more sooty plug.

And....the fuel height in #2 is a couple of mm below the gasket while the engine is running.

The sooty plug on cylinder #2 is intermittent. It is either a carb problem or possibly valves or piston rings, etc.

[skids]

A bad valve seal will cause smoke during deceleration and can cause oil fouling. You might want to switch to a hotter plug. NGK 6 is hotter than NGK 7. (Forgot the rest of the plug designations...)

[Bonz]

I would assume he has the BP6ES plugs, but I don't see that he said.

If it is intermittent, meaning it gets sooty sometimes and not others, that would not be internal issues with the engine or valve seals. It would do it consistently, those things don't come and go, IMO.

Have you cleaned up the end of the plug wire (removed 1/4-1/2") and giving it a fresh connection to the plug cap? When you moved to #3 you may have jiggled it and the connection got better. When you moved it back to #2 it went back to its old position, and is now intermittent versus not working well at all.

[HalfCentury]

The XJ1100 plugs are new and are BP6ES.

I have not yet performed any plug wire modifications.

The coils and wires and plug caps are 36-ish years old. It may be time to just perform the replacement of the coils and wires. It appears that this is a much simpler exercise than removing and replacing the carbs or the valve shim adjustment.

The bike probably has 40k-ish miles on it. The odometer showed 36k when I bought it but the odo was broken. I replaced the speedometer/odometer with an XS650 120mph unit.

The condition of the brake fluid when I bought the bike leads me to believe that previous owners performed zero maintenance.

[Bonz]

If you cut off the end of the wire at the plug cap and reinsert, you have fresh wire. It's so simple. I would recommend that before buying new wires all around.