Cylinder 3 wont fire... at a complete loss

[sethhope]

First off, hello all!

So I recently ran across a pretty cheap 1979 xs1100f on Craigslist. Ive never owned a bike before, but my dad has owned many and agreed to help out where he can. After some evaluation, the bike seems to need some basic maintenance. Its beem garaged it's whole life, but hasnt run in a few years.

What I did:
Fixed some screw ups in the wiring by the previous owner (he removed the cutoff switch, but grounded the wires to the bars)
Quick clean of the carbs (removed, dropped the bowls, removed jets and soakes in cleaner)
New fluids and filters
Inline fuel filters (petcock ones were shot)
Petcock rebuild
Replaced p/o coil wires
Check all coils and caps (in spec)
Checked spark on all cylinders (great)
New battery
New starter solinoid
New fused/cleaned fuse box
Drained, cleaned, and treated gas tank

After all of this, my 3 cylinder is cold. Im getting good spark. The plug isn't wet when pulled. All the jets are clear and cleaned. The floats are moving properly along with the pin. The bowl fills properly with gas but doesn't over fill. It doesnt seem to be flooding, but i have a hard time believing that its not getting fuel... my last thought is that it may be a pinhole in my diaphragm, but im going to check that tomorrow morning. Any insite into what could be causing this is helpful.

Thanks, Seth

P.s. if this is in the wrong section, please gut me accordingly

[Schming]

First off, hello all!

So I recently ran across a pretty cheap 1979 xs1100f on Craigslist. Ive never owned a bike before, but my dad has owned many and agreed to help out where he can. After some evaluation, the bike seems to need some basic maintenance. Its beem garaged it's whole life, but hasnt run in a few years.

What I did:
Fixed some screw ups in the wiring by the previous owner (he removed the cutoff switch, but grounded the wires to the bars)
Quick clean of the carbs (removed, dropped the bowls, removed jets and soakes in cleaner)
New fluids and filters
Inline fuel filters (petcock ones were shot)
Petcock rebuild
Replaced p/o coil wires
Check all coils and caps (in spec)
Checked spark on all cylinders (great)
New battery
New starter solinoid
New fused/cleaned fuse box
Drained, cleaned, and treated gas tank

After all of this, my 3 cylinder is cold. Im getting good spark. The plug isn't wet when pulled. All the jets are clear and cleaned. The floats are moving properly along with the pin. The bowl fills properly with gas but doesn't over fill. It doesnt seem to be flooding, but i have a hard time believing that its not getting fuel... my last thought is that it may be a pinhole in my diaphragm, but im going to check that tomorrow morning. Any insite into what could be causing this is helpful.

Thanks, Seth

P.s. if this is in the wrong section, please gut me accordingly

Welcome Seth, sounds like the starter jet circut or pilot fuel jet circut may be clogged.

[GLoweVA]

Seth, i helped a fellow xsive with a very similar problem. He had no combustion in #3 either. Turned out the carb body had an issue and it wouldn't suck any fuel up from the bowl. He put a new carb in there and viola. It worked.

He bench tested his carb rack with water for a fuel source and used a shop vac to simulate the piston sucking action and #3 failed miserably while the other 3 performed great at sucking water from the bowl.

[motoman]

Sethhope, My guess would be the #3 fuel pick-up circuit in bottom of fuel bowl is plugged. Try removing #3 fuel bowl and blowing carb cleaner thru it checking that it is clear and open.

[HalfCentury]

The "Spray Test" for a fuel bowl enrichment circuit. You may have to click "replay" to see the 3-second video.

Make sure your eyes are covered and that you point it away from yourself.

https://www.youtube.com/watch?v=9yBwrcqwArA

[Eastcoaster]

compression

Seth just to rule it out did you do a compression test on all cylinders.
I am local to you if you need help let me know. I can take a ride up and give you a hand. Lots of little tricks to the carbs to get them clean. I would be glad to point you in the right direction

[sethhope]

Seth just to rule it out did you do a compression test on all cylinders.
I am local to you if you need help let me know. I can take a ride up and give you a hand. Lots of little tricks to the carbs to get them clean. I would be glad to point you in the right direction

I did do a compression check and it read 120 on the nose. As for the help, i really appreciate the offer, but im a bit further out than my profile says. I dodnt get to changing that last night. Im actually closer to philly pa...

[Bonz]

For sure, rule out major blockages of the main jets and pilot circuits like you said you did, but check if the needle is letting fuel past once the carbs are on the bike. Maybe the float is getting hung up (on a float bowl gasket is one place, make sure the edges are trimmed so none stick out) and keeping the needle from opening and letting more fuel in once on the bike. Just a thought, let us know what you find.

A pinhole in the diaphragm wouldn't keep fuel from flowing with the pilot circuit, so I don't think your issue lies there, but it's good to look if you have any pinholes. Liquid plasti-dip or liquid electrical tape works well to touch up those holes if you find any.

[sethhope]

For sure, rule out major blockages of the main jets and pilot circuits like you said you did, but check if the needle is letting fuel past once the carbs are on the bike. Maybe the float is getting hung up (on a float bowl gasket is one place, make sure the edges are trimmed so none stick out) and keeping the needle from opening and letting more fuel in once on the bike. Just a thought, let us know what you find.

A pinhole in the diaphragm wouldn't keep fuel from flowing with the pilot circuit, so I don't think your issue lies there, but it's good to look if you have any pinholes. Liquid plasti-dip or liquid electrical tape works well to touch up those holes if you find any.

Fuel is getting into the bowl, and it doesn't seem that the float is sticking. I checked the gasket and its all nice and trimmed flush. Maybe the float height is off...? Though it seems (visually) equal to the others...

[Bonz]

Just to verify, the carbs start dry and when you put them on the bike, the bowl fills like you are describing? Is the float filled with gas? if so, could be sinking and allowing fuel to fill the bowl, then raising back up in a full bowl and cutting off the flow. You have the brass floats, correct? I don't know if that makes sense, but I am just putting ideas out there.

[sethhope]

Just to verify, the carbs start dry and when you put them on the bike, the bowl fills like you are describing? Is the float filled with gas? if so, could be sinking and allowing fuel to fill the bowl, then raising back up in a full bowl and cutting off the flow. You have the brass floats, correct? I don't know if that makes sense, but I am just putting ideas out there.

How would i check if they are filling? I didnt see or feel gas in them when I took the bowls off, but could they have drained in the time disassembly took?

[Bonz]

First off, hello all!

So I recently ran across a pretty cheap 1979 xs1100f on Craigslist. Ive never owned a bike before, but my dad has owned many and agreed to help out where he can. After some evaluation, the bike seems to need some basic maintenance. Its beem garaged it's whole life, but hasnt run in a few years.

What I did:
Fixed some screw ups in the wiring by the previous owner (he removed the cutoff switch, but grounded the wires to the bars)
Quick clean of the carbs (removed, dropped the bowls, removed jets and soakes in cleaner)
New fluids and filters
Inline fuel filters (petcock ones were shot)
Petcock rebuild
Replaced p/o coil wires
Check all coils and caps (in spec)
Checked spark on all cylinders (great)
New battery
New starter solinoid
New fused/cleaned fuse box
Drained, cleaned, and treated gas tank

After all of this, my 3 cylinder is cold. Im getting good spark. The plug isn't wet when pulled. All the jets are clear and cleaned. The floats are moving properly along with the pin. The bowl fills properly with gas but doesn't over fill. It doesnt seem to be flooding, but i have a hard time believing that its not getting fuel... my last thought is that it may be a pinhole in my diaphragm, but im going to check that tomorrow morning. Any insite into what could be causing this is helpful.

Thanks, Seth

P.s. if this is in the wrong section, please gut me accordingly

You mentioned above the bowls fill properly, so I gathered you were testing that. Am I min-understanding what you are saying? Sorry if I am.

If the float was leaking and letting gas in, it would be obvious if you took the float off and shook it around. Slosh, Slosh.

[HalfCentury]

How would i check if they are filling? I didnt see or feel gas in them when I took the bowls off, but could they have drained in the time disassembly took?

Barring Xray vision, you probably have to remove the bowl, place it on your bench, fill it with fuel and see if the float floats.

While you have the bowl off, do the spray test as per the video.

When I did my XJ650 carbs, the enrichment circuits were completely clogged. You cannot see the clog since the circuit is a minuscule width passage. I boiled my bowls in lemon juice, removed one bowl at a time and did the spray test to clear the circuit while the bowl was hot and the clog was softened.

[Bonz]

Good idea on boiling to soften up any gunk!

[sethhope]

Update. I soaked the carbs again. This time a full disassembly. The floats float and the pin isnt getting stuck. The diaphragm is beautiful as well as pretty much the whole carb assembly. I pulled the jets and sprayed them out with cleaner and compressed air. Put everything together and still nothing on 3... im at a complete loss... it pops and sputters, but never heats up. Good spark, clean carbs... pardon my frustration but WHAT'S GOING ON HERE???