1981 XS650 Jerking

[irishfire11]

Hello all, new to this site but looking for answers. Two weeks ago I got an 81 from a friend. He hasn't ridden it much but has never had any issues in the year he's owned it. I've put about 250 miles on it since I got it and it's ran great. Mostly highway/town with a tiny bit of interstate driving. I took it out to get lunch across town yesterday with zero issues. Took it out again about 4 hours later and I noticed once I started picking up speed out of town it started jerking back in quick spurts, almost as if the fuel was being cut off extremely quickly and back on in intervals. The bike jerks back as it loses speed and then picks up again. This all happens very quickly within maybe half a second.
I noticed the oil was low so I put a quart in and it seems to help a little bit. Not sure if it's actually helping though. The jerking is really random. The chain is tightened properly. I opened up the carbs and did notice a little bit of particles in the fuel filters within the carbs but it didn't seem like enough to actually prevent fuel flow. Any thoughts?

 

[jetmechmarty]

Next time it does it, open the fuel cap and see if it stops. Is there an inline fuel filter?

 

[jpdevol]

This all happens very quickly within maybe half a second.
I noticed the oil was low so I put a quart in and it seems to help a little bit. Not sure if it's actually helping though.

As Marty said: could be a plugged vent in fuel cap. It is also a classic symptom of some water accumulated in the float bowl; perhaps drain some into a clear container to check for typical separation of the fluid.

Also, these motors only hold a little over two quarts; adding a quart is a lot. They don't like being overfilled. Below is old Serv. Bulletin, but it's applicable still.

 

[gggGary]

do you have a voltmeter you can see while you are riding?
Erratic running as the first sign of low voltage is VERY popular with TCI bikes. (80 to 84 are TCI ignition)
At the very least shore charge the battery before you head out again see if the erratic running takes longer to show up.

 

[irishfire11]

Next time it does it, open the fuel cap and see if it stops. Is there an inline fuel filter?

There isn't any type of fuel filter other than the ones inside the carbs which def isn't ideal. But I will try to run it with the cap open later today after work. Thank you

 

[irishfire11]

As Marty said: could be a plugged vent in fuel cap. It is also a classic symptom of some water accumulated in the float bowl; perhaps drain some into a clear container to check for typical separation of the fluid.

Also, these motors only hold a little over two quarts; adding a quart is a lot. They don't like being overfilled. Below is old Serv. Bulletin, but it's applicable still.
View attachment 224513

I had already opened and emptied the bowls when I posted but I suppose that sounds be taken care of anyways

 

[irishfire11]

do you have a voltmeter you can see while you are riding?
Erratic running as the first sign of low voltage is VERY popular with TCI bikes. (80 to 84 are TCI ignition)
At the very least shore charge the battery before you head out again see if the erratic running takes longer to show up.

The battery has been giving me some slight issues. It doesn't seem to want to stay charged, but the only other symptom I've seen of this is it getting low and but wanting to start

 

[jpdevol]

If there was water in the bowls, and the problem reappears after the battery is replaced (sounds due for one), you may want to check for water in the tank.

On the battery, seems the consensus here favors a sealed acid type over LiFePo or old vented lead-acid: 12V 14AH, YB14L-A2

How's your oil level?

 

[gggGary]

You need to know what your charging system is up to. Small hsndlebar mount voltmeter usb are cheap n useful.
Alternator brushes are a #1 needs doing item

 

[JJames]

Yep. Charging issues resulting in low voltage will certainly cause the type of cutting-out that you described.