#2 cylinder dead at low RPM

[warlock60]

'79 XS1100 Special #2 cylinder dead at lower RPM. It has very nice top end, but runs rough at lower rpm. I stopped at a local park and took one plug wire off at a time and found the rpm didn't change when I removed the #2 plug wire. Ran it down the road like that and it acted the same as with the wire on.
Got home and put an old spark plug on the end of the wire and found nice hot spark. Soooo, my question is which jet in the number two carb is more likely than not the culprit?

I just got back from an "all expense paid visit" to Afghanistan, but before I left I put SeaFoam in the tank. The bike started right up, but I'm afraid maybe in spite of the preventive seafoam it may still have a gummed jet. I don't know, but before I go through the trouble of taking off the carb and cleaning it, I would run this by you guys. Any thoughts??

Ray

[natemoen]

After sitting for a while, seafoam or not, it wouldn't hurt to go through and clean the carbs.

[XS1100_OEM4ME]

Sounds like R/I the carbs for cleaning. You could run some carb cleaner tank add through, but if it is not fireing at all, will not be good on the cyl, good luck

[mharrington]

Had this happen in september. One cyl was dead until 2000-2500rpm then it was on all 4. The pilot jet in that carb is plugged. Pilot jet delivers fuel at lower rpm. Above 2500ish RPM that circuit does not supply fuel and the main jet takes over. have a long thin blade screwdriver with a good robust tip and unscrew the pilot jet and clean. Mine had a brown gritty paste plugging it. I removed the needle/seat assembly and cleaned the same gunk from the dome screen. Its an easy fix- the most undesirable part is removing and re installing the carbs as the boots to the air box make it a pain. On a scale of 1 to 10 (10 being the most difficult) I rate this task at 4.

[natemoen]

Had this happen in september. One cyl was dead until 2000-2500rpm then it was on all 4. The pilot jet in that carb is plugged. Pilot jet delivers fuel at lower rpm. Above 2500ish RPM that circuit does not supply fuel and the main jet takes over. have a long thin blade screwdriver with a good robust tip and unscrew the pilot jet and clean. Mine had a brown gritty paste plugging it. I removed the needle/seat assembly and cleaned the same gunk from the dome screen. Its an easy fix- the most undesirable part is removing and re installing the carbs as the boots to the air box make it a pain. On a scale of 1 to 10 (10 being the most difficult) I rate this task at 4.

Yeah but he said it acts the same while driving with the plug wire off as when it is on, so that means it is most likely never firing, so everything in there is clogged up.

[L0rdexpectati0n]

disconnect the spark plug crank it over a couple times and pull the spark plug to see if it is "wet" if not trace the flow of gas back from there

[mharrington]

Yeah but he said it acts the same while driving with the plug wire off as when it is on, so that means it is most likely never firing, so everything in there is clogged up.

I stand corrected. Since the crabs come off in one bank he should just clean all 4 carbs and both petcocks. When I got my XS1100F in sept of 2010 the dome screens that fit over the seat unit was plugged with gunk as well as the fuel tank petcock screens. I currently have 2 fuel filters in each line but I think filters with the paper element will filter better than the porous metal element? Unfortunately with old bikes it mandates this type of tinkering. On the plus side- clean everything real good, quality fuel line and inline filters and it should be a long time before it needs to be done again.

[mharrington]

Oh- make sure all the plugs are securely covering the nipples on the intake rubber boots! I forgot to reinstall one and was ready to hang it up when I started up after a thorough cleaning just to hear the sound of 3 cylinders hitting.

[James England]

Its an easy fix- the most undesirable part is removing and re installing the carbs as the boots to the air box make it a pain.

It needn't be that way though. After reading a thread here, I removed my carbs. The trick is to partially undo the bolts which hold the top of the airbox to the frame... not too far though, as they come disconnected inside the box if you unscrew too much. After removing the bottom half of the airbox and the filter, of course. This gives just enough slack to push the front bracket of the airbox forward and down and the airbox will drop down towards the engine, backwards and away from the carb mouths. It really is very easy to remove and replace the carbs if you do this.

[XS1100_OEM4ME]

I pop the upper bracket that slides back and forth over the post that is welded to the frame, off it with a large screwdriver, then drop down the air box with filter removed. When I reassemble, I can guild the intake tubes on one at a time by reaching up inside the airbox and pushing them on one at a time

It needn't be that way though. After reading a thread here, I removed my carbs. The trick is to partially undo the bolts which hold the top of the airbox to the frame... not too far though, as they come disconnected inside the box if you unscrew too much. After removing the bottom half of the airbox and the filter, of course. This gives just enough slack to push the front bracket of the airbox forward and down and the airbox will drop down towards the engine, backwards and away from the carb mouths. It really is very easy to remove and replace the carbs if you do this.

[James England]

I pop the upper bracket that slides back and forth over the post that is welded to the frame, off it with a large screwdrive

Exactly. Prising it forward is just a bit less forceful if the four bolts are loosened a bit though. Until I read the thread here, I'd struggled for years with those damned boots

[natemoen]

I just cut that little part off that bracket, no problems since

[crazy steve]

The trick to reinstalling the carbs/airbox is simple... To remove the carbs, take the airbox bolts out and push back as far as it'll go. This will disengage the carbs so you can pull them.

To reinstall, put the carbs on the intake boots, then angle the airbox so you can get two of the boots started. You'll get the outer boot almost all the way on, the next one in partially; it doesn't matter which side you do. Install the rear airbox bolt on that side (so the box can't move back), then lever the other side on. Once I figured that out, getting the airbox back on the carbs became a few-minute exercise....

[XS1100_OEM4ME]

I don't know if there is much difference on the 79SF I have, but if I dont get the airbox off the frame shaft and down and back, It is too tight to get the carbs out without bending the intake manifolds Just my experance on my bike, not saying others have the same clearance

The trick to reinstalling the carbs/airbox is simple... To remove the carbs, take the airbox bolts out and push back as far as it'll go. This will disengage the carbs so you can pull them.

To reinstall, put the carbs on the intake boots, then angle the airbox so you can get two of the boots started. You'll get the outer boot almost all the way on, the next one in partially; it doesn't matter which side you do. Install the rear airbox bolt on that side (so the box can't move back), then lever the other side on. Once I figured that out, getting the airbox back on the carbs became a few-minute exercise....

[bikerphil]

I cut the snorkel down and the air box comes out easily before the carbs, no center top bracket either.