Stumbling

[HalfCentury]

One more thing. Is your exhaust system in good shape? Strange things can happen when a baffle is shot.

The left side muffler has an external crack that has a temporary tomato can clamped around the crack. Cylinder 1 shares this muffler and cylinder 1 has no fouling problem.

[Schming]

I performed a dry compression test. 130 PSI across all four cylinders. I guess this means that a second appointment with the carbs is in my future. I much prefer a second appointment with the carbs than appointment with the piston rings or valves.

Compression numbers are good. If you already set the valves then you should be good as far as internals of the engine are concerned as these monsters are pretty much bullet proof.

I'm gonna guess #2 has a float hanging up.

Test the floats with an auxiliary fuel source before reinstalling the carbs.

[DiverRay]

Here is a post I did for carbs:
1. Make SURE the vent tube, top "T" fitting, is not blocked! ('78-80)
2. Check that the floats do not "hang up" on the bowl gasket
3. verify that all 4 floats are set to EXACTLY the same height
4. Bench test the carbs, use a "C" clamp to secure to a 2X6 or something to keep them level, turn upside down, and put fuel into one pair at a time. Thee should be NO FUEL flowing out of the carbs. Once they hold that way, install bowls, flip over and add fuel again, one pair at a time. I keep a remote tank with shutoff and have it about 2' above the carbs. Let it set for 5 minutes per side, looking for any leaks.
This should help you get to the bottom of it!

[Bonz]

I like the idea of a baffle being shot, however that would also affect more than one cylinder, IMO.

Could a damaged carb diaphragm cause an overly rich condition in one cylinder? It is something that is affecting only one cylinder, so it would be confined to one carburetor.

[motoman]

I like the idea of a baffle being shot, however that would also affect more than one cylinder, IMO.

Could a damaged carb diaphragm cause an overly rich condition in one cylinder? It is something that is affecting only one cylinder, so it would be confined to one carburetor.

As Bonz stated pertaining to diaphragm, pinholes in diaphragm(caused in 6-8 locations from rubbing inner portion of diaphragm assembly) would cause lack of vacuum in that assembly and not allow vacuum to hold slide/metering rod down far enough causing richness.

[Schming]

I like the idea of a baffle being shot, however that would also affect more than one cylinder, IMO.

Could a damaged carb diaphragm cause an overly rich condition in one cylinder? It is something that is affecting only one cylinder, so it would be confined to one carburetor.

A damaged (leaking) diaphragm would not let the barrel raise evenly with the other 3 if at all. Therefore the main jet needle wouldn't raise and cause a lean condition.

[Schming]

As Bonz stated pertaining to diaphragm, pinholes in diaphragm(caused in 6-8 locations from rubbing inner portion of diaphragm assembly) would cause lack of vacuum in that assembly and not allow vacuum to hold slide/metering rod down far enough causing richness.

The spring holds the barrel down

[skids]

A damaged (leaking) diaphragm would not let the barrel raise evenly with the other 3 if at all. Therefore the main jet needle wouldn't raise and cause a lean condition.

I have to agree with that. The spring should push the main needle down unless there is vacuum above the diaphragm.

[motoman]

The spring holds the barrel down

Appreciate you correcting my backwards thinking.

[Bonz]

OK, think of this... so the diaphragm doesn't/won't lift much/any, however there is still negative pressure being exerted above the diaphragm that transfers down through the hole/tear or improperly seated diaphragm lip and could pull fuel up from the main jet as the needle doesn't completely plug the jet hole and the cylinder would be getting little/no air. JAT, but it's JAT. That's how my mind works, but there may be no basis in physics for it to happen.

[BA80]

Have the diaphragms been replaced or do they spin on the slides? If the vent hole isn't front and center, towards the engine, the slide won't raise.

Ran into that once on a used set of carbs.

[HalfCentury]

Have the diaphragms been replaced or do they spin on the slides? If the vent hole isn't front and center, towards the engine, the slide won't raise.

Ran into that once on a used set of carbs.

I do not think that the diaphragms rotate. I will check the vent hole orientation when I remove the carbs.

Tomorrow I will be taking the bike for the cursory annual inspection. I have to do it this week to meet the annual deadline. When I am back from the inspection, I will be removing the carbs for a thorough teardown. This is where I wish I had a set of XJ carbs on the shelf all pristine and ready to install.

Anyone have a set of XJ11 carbs they do not need?

[tcoop]

I have a complete set but the #1 (or #4 I cant remember) carb has an issue. So they are not pristine. If you want them $50 plus shipping. I was keeping them for parts. PM me if you are interested.

[HalfCentury]

The carbs are off and drying in front of a fan on my driveway. The intake manifold boot of cylinder #2 looks wet. Hope I can chase down the rich problem in carb #2.

[Ranger_xs1100]

Brilliant BA80!

Have the diaphragms been replaced or do they spin on the slides? If the vent hole isn't front and center, towards the engine, the slide won't raise.

Ran into that once on a used set of carbs.

Thank You BA80! I have been fighting a serious off idle hesitation/stumble for weeks now on my new to me 79SF. The bike came with a mac 4 into 2 exhaust, and I put pod filters on it. I figured it had to be a matter of getting the jetting right. I tried every combination that I could think of without much improvement and sometimes making it worse. Then I read your post about the slide vent hole orientation, something that I never thought of before... and sure enough, the holes were pointing in 4 different random directions. The rubber diaphragms were loose and could easily be turned on the slide. I aligned the holes facing the engine and put a little RTV around the rubber and plastic joint to prevent the rubber from from rotating. I also found aftermarket needles in the slides so I put in the correct OEM needles. What a huge difference! Thank you for your brilliant insight!